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Topic 4 – Acids and Bases (Part A) Some information about acids you need to

REMEMBER:

Hydrochloric acid

Sulphuric acid

Nitric acid

Sulphurous acid

Carbonic acid

Ethanoic acid

Phosphoric acid

HCl 氫氯酸

H2SO4 硫酸

HNO3 硝酸

H2SO3 亞硫酸

H2CO3 碳酸

CH3COOH 乙酸

H3PO4 磷酸

H+

Cl-

2H+

chloride

in stomach juice

SO42-

H+

sulphate

NO3-

nitrate

SO32-

2H+

sulphite

2H+

in car battery

CO32-

carbonate

in soft drink

Citric acid

Oxalic acid

檸檬酸

草酸

(a solid at room temerpature)

Ethanoate

3H+

PO43phosphate

in vinegar(醋)

Definition of an acid: An acid is a hydrogen-containing compound, which can produce hydrogen ions H+(aq) as only cations after dissolving in water.

2H+ 3H+

CH3COO-

H+

Ca/Mg/Zn/Fe/Cu + HCl:

oxalate

Properties of H2(g):

Chemical reaction of acid 1 of 3: reaction between acid and metals

citrate

in citrus fruits

Metal + dilute acid  Salt + Hydrogen gas 非常稀的

稀的

濃的

 Observations:  Metal dissolves / colorless gas bubbles produced  Test for hydrogen gas  Give a pop sound with burning splint  K and Na will not put into acid  explosive reaction

These three acids react with metal differently. Redox reactions, learn them later!

Write a chemical equation and an ionic equation for each of the reactions below: Example: magnesium + dilute sulphuric acid (a) Chemical equation

(b)

Mg(s) + H2SO4(aq)  MgSO4(aq) + H2(g)

1.

Ionic equation Mg(s) + 2H+(aq)  Mg2+(aq) + H2(g)

zinc + dilute sulphuric acid (a) Chemical equation

(b)

Ionic equation

 2.

iron + dilute hydrochloric acid (a) Chemical equation

(b) 

Ionic equation 

H+(aq) is important for the above chemical reactions. How is this H+(aq) formed from the acid molecules? Ch 14 Introduction of acid and alkalis / Ch 16 Indicator and pH / Ch 17 Strength / Ch 18 Salt and neutralization

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Topic 4 – Acids and Bases (Part A) Ionizaition of HCl molecules in water: ionization

3. Ionization of H2SO4 molecules in water: ionization

H+

(hint: p.1 information)

Mg(s) + 2H+(aq)  Mg2+(aq) + H2(g)

Zn(s) + 2H+(aq)  Zn2+(aq) + H2(g) 4. Explain the role of water for sulphuric acid to show its acidic properties (i.e. react with Zn to produce H2(g)).

Example: Each HCl molecule is ionized into

water to produce one hydrogen ion and

__________________________________________ __________________________________________

one chloride ion. Hydrogen ions react with magnesium metal to

__________________________________________

produce hydrogen gas.

__________________________________________

 Water is important for ionization of acid molecules.

5. Explain why Mg has no reaction with HCl in methylbenzene. Methylbenzene contains no _____________, HCl cannot ______________ to produce _________________ _________ . Acidic properties

Hydrogen chloride in methylbenzene (= no water)

(1) Effect on dry blue litmus paper

Remains blue

(2) Addition of Mg

No reaction

(3) Conductivity test

Light bulb does not glow

Hydrogen chloride in water Turns red Observation:  Mg dissolves  Gas bubbles produced Light bulb glows

Different kinds of acid molecule, different no. of hydrogen ions from ionization?

Ch 14 Introduction of acid and alkalis / Ch 16 Indicator and pH / Ch 17 Strength / Ch 18 Salt and neutralization

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Topic 4 – Acids and Bases (Part A) Classification of acid (1)

= degree of ionization in water (extent of dissociation) in water

by strength (強度)

Strong acid (強酸)

Weak acid (弱酸)

completely ionized in water

Incompletely / Partly / Slightly ionized in water

HCl(aq)  H+(aq) + Cl-(aq)

HCl

H2SO4

H+(aq) + CH3COO-(aq)

CH3COOH(aq)

HNO3

H2SO3

H2CO3

Example: 6. Which acid will give bubbles in a faster rate with Mg? 1M HCl or 1M CH3COOH? 1M HCl will give bubbles at a faster rate.

CH3COOH

H3PO4

Citric acid

1M carbonic acid or 1M HNO3? _____________________________________ _____________________________________

Because HCl is a strong acid but CH3COOH is a

_____________________________________

weak acid, HCl can completely ionized into water.

_____________________________________

HCl contains higher concentration of hydrogen

_____________________________________

ions than CH3COOH.

_____________________________________ number of H (aq) can be produced when an acid molecule is ionized into water +

Classification of acid (2)

by basicity (鹽基度)

Monobasic acid (一元酸)

Dibasic acid (二元酸)

Tribasic acid (三元酸)

ONE ionizable hydrogen atom per acid molecule

TWO ionizable hydrogen atom per acid molecule

THREE ionizable hydrogen atom per acid molecule

HCl(aq)  H+(aq) + Cl-(aq)

H2SO4(aq)  2H+(aq) + SO42-(aq)

HCl

HNO3

CH3COOH

H2SO4

H2SO3

Example : 7. Which acid will give bubbles in a faster rate with Mg? 1M HCl or 1M H2SO4? 1M H2SO4 will give bubbles at a faster rate. Because H2SO4 is a dibasic acid but HCl is a monobasic acid, H2SO4 contains higher concentration of hydrogen ions than HCl.

H2CO3

H3PO4(aq) H3PO4

3H+(aq) + PO43-(aq) Citric acid

0.1M HNO3 or 0.1M H2SO4? _____________________________________ _____________________________________ _____________________________________ _____________________________________ _____________________________________

Ch 14 Introduction of acid and alkalis / Ch 16 Indicator and pH / Ch 17 Strength / Ch 18 Salt and neutralization

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Topic 4 – Acids and Bases (Part A) Conductivity test for a solution:

ďƒ&#x; conductivity test for distinguishing between distilled water / NaCl(aq) / HCl(aq) / H2SO4(aq)

Example: Which solution will give a larger brightness of bulb?

or 8. Which of the following solutions has the lowest electrical conductivity? A. B. C. D.

0.1 M carbonic acid 0.1 M nitric acid 0.1 M hydrochloric solution 0.1 M sulphuric acid

?

1M HCl or 1M CH3COOH? 1M HCl will give bubbles at a faster rate. Because HCl is a strong acid but CH3COOH is a weak acid, HCl can completely ionized into water. HCl contains *more mobile ions* than CH3COOH.

Explanation: 10. ______________________________________ ______________________________________ ______________________________________ ______________________________________ *Generally, strength is a more dominant factor than basicity.

9.

Which of the following statements concerning the set-ups are correct? (1) The light bulbs in both set-ups will glow. (2) The light bulb in set-up Y will glow brighter. (3) Both solutions in the set-ups contain mobile electrons. A B C D

Which of the following solutions will make the bulb the brightest? A 25 cm3 of 0.5 M H2SO4(aq) B 25 cm3 of 0.5 M HCl(aq) C 25 cm3 of 0.5 M CH3COOH(aq) D 25 cm3 of 0.5 M citric acid

(1) and (2) only (1) and (3) only (2) and (3) only (1), (2) and (3)

11. Draw an experimental set-up for conductivity test:

Ch 14 Introduction of acid and alkalis / Ch 16 Indicator and pH / Ch 17 Strength / Ch 18 Salt and neutralization

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Topic 4 – Acids and Bases (Part A) 12.

The strength of an acid is determined by A the number of hydrogen ions present. B its concentration. C its degree of ionization in water. D its ability to change the colour of litmus solution.

13.

Which of the following acids is a strong acid? A Ethanoic acid B Citric acid C Carbonic acid D Hydrochloric acid

14.

Which of the following acids is a weak acid?

15.

Which of the following statements concerning citric acid is correct?

A B C D

Sulphuric acid Citric acid Nitric acid Hydrochloric acid

A B C D

*16.

Which of the following particles is NOT a main constituent of dilute hydrochloric acid? A B C D

Hydrogen chloride molecules Hydrogen ions Water molecules Chloride ions

17.

It is a strong acid. It is present in lemons. Its aqueous solution does not conduct electricity. It exists as a liquid at room temperature and pressure.

Vinegar is a weak acid because A B C D

it is not corrosive. it has a pH value lower than 7. it slightly ionizes in water. it is an organic acid.

18. What is the basicity of ethanoic acid? A 1 B 2 C 3 D 4

19. Which of the following has / have a basicity of three? (1) NH3(aq) (2) H3PO4(aq) (3) CH3COOH(aq) A (1) only B (2) only C (1) and (3) only D (2) and (3) only

20. The basicity of an acid is

*21. H3PO4 is a tribasic acid. Which of the following formulae is INCORRECT?

A B C

D

a measure of the strength of the acid. the maximum number of hydroxide ions produced from one acid molecule. the maximum number of hydrogen ions produced from one acid molecule when it is ionized into water directly proportional to the concentration of the acid.

A B C D

(NH4)2HPO4 NaH2PO4 AlPO4 KPO4

Besides reaction rates, higher concentration of H+(aq), pH value will be ( higher / lower ) ? Ch 14 Introduction of acid and alkalis / Ch 16 Indicator and pH / Ch 17 Strength / Ch 18 Salt and neutralization

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Topic 4 – Acids and Bases (Part A) The pH scale  All aqueous solutions contains H+(aq) and OH-(aq) Acidic

+

[H

(aq)]

>

[OH-(aq)]

[H+(aq)] = [OH-(aq)]

Alkaline

[H (aq)] < [ ] = concentration +

[OH-(aq)]

: pH = -log[H+] pH =

pH =

pH =

pH =

22. Calculate the pH values with given concentrations of H+(aq) given in the table.

pH =

pH =

[H+] = 1 M

[OH-] = 1

[H+] = 1 x 10-1 M

[H+(aq)] 

pH 

e.g. 0.1M HCl

[H+] = 1 x 10-2 M

W: 0.01 M HNO3(aq) X: 0.01 M H2SO4(aq) Y: 0.01 M KOH(aq) Z: 0.1 M KOH (aq)

[H+] = 1 x 10-3 M [H+] = 1 x 10-4 M

Increasing order of pH : ____ < ____ < ____ < ____

pH =

x 10-11 M

[OH-] = 1

x 10-10 M

e.g. acid rain (pH < 5.6)

[H+] = 1 x 10-5 M

[OH-] = 1

x 10-9 M

e.g. wine, normal rainwater

[H+] = 1 x 10-6 M

[OH-] = 1

x 10-8 M

[OH-] = 1

x 10-7 M

e.g milk

1. 2.

Distilled water Salt formed by strong acid and strong alkali (e.g. NaCl, Na2SO4)

[H+] = 1 x 10-8 M

[OH-] = 1

x 10-6 M

e.g. toothpaste

[H+] = 1 x 10-9 M

[OH-] = 1

x 10-5 M

e.g. baking soda (NaHCO3) [OH-] = 1

x 10-4 M

e.g. ‘Milk of Magnesia’

[H+] = 1 x 10-11 M

[OH-] = 1

x 10-3 M

e.g. ammonia solution NH3 + H2O

pH =

[OH-] = 1

e.g. vitamin C (ascorbic acid)

pH =

pH =

x 10-12 M

e.g. lemon juice (citric acid), vinegar (ethanoic acid)

[H+] = 1 x 10-10 M

pH =

[OH-] = 1

[H+] = 1 x 10-12 M

NH4+ + OH[OH-] = 1

x 10-2 M

e.g. limewater (calcium hydroxide)

[H+] = 1 x 10-13 M [H+]

[OH-] = 1

x 10-1 M

e.g. oven cleaner, 0.1M NaOH [OH-] = 1 M = 1 x 10-14 M

[H+] << [OH-] highly alkaline

[13DSE/MC#10] 23. Consider the four solutions W, X, Y and Z listed below:

x 10-13 M

[H+] < [OH-] slightly alkaline

pH =

[OH-] = 1

[H+] =[OH-] neutral

pH =

x 10-14 M

e.g. 1M HCl, 1M HNO3

[H+] = 1 x 10-7 M pH =

(at room conditions)

[H+] > [OH-] slightly acidic

pH =

: pH + pOH = 14

[H+] >> [OH-] highly acidic

Neutral

pH of different substances

e.g. 1M NaOH (caustic soda)

Ch 14 Introduction of acid and alkalis / Ch 16 Indicator and pH / Ch 17 Strength / Ch 18 Salt and neutralization

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Topic 4 â&#x20AC;&#x201C; Acids and Bases (Part A) Example: Explain why pH of 0.01 M H2SO4(aq) is smaller than that of 0.01 M HNO3(aq).

24. The pH value of 0.1 M hydrochloric acid is about 1 but that of 0.1 M ethanoic acid is about 3. Why? ____________________________________________

Because H2SO4 is a ________________ acid but HNO3 is a ________________ acid.

____________________________________________

H2SO4 has a higher ________________of

____________________________________________

__________________ ___________. ____________________________________________ Therefore, pH of 0.01 M H2SO4(aq) is smaller than that of 0.01 M HNO3(aq)

____________________________________________

Acid-alkali indicator: a dye which its color is sensitive to change of [H+(aq)]

pH measurement: 1. Universal indicator / pH paper: a mixture of acid-alkali indicators

2. pH meter: accurate measurement of pH

Ch 14 Introduction of acid and alkalis / Ch 16 Indicator and pH / Ch 17 Strength / Ch 18 Salt and neutralization

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Topic 4 – Acids and Bases (Part A) 25. Which of the following statements about a neutral aqueous solution at room conditions is correct? A. B. C. D.

H+(aq) concentration > OH(aq) concentration H+(aq) concentration = OH(aq) concentration H+(aq) concentration < OH(aq) concentration There is no H+(aq) ion and OH(aq) ion.

27. Which of the following substances has a pH value above 7 at room conditions? A. B. C. D.

Limewater Soft drinks Rainwater Orange juice

29. Which of the following substances is NOT an acid-alkali indicator? A. B. C. D.

Methyl orange Limewater Phenolphthalein Litmus

*31. Which of the following solutions are neutral? (1) (2) (3) (4)

HCl(aq) NaCl(aq) NaOH(aq) Na2SO4(aq)

A. B. C. D.

(1) and (2) only (1) and (3) only (2) and (4) only (3) and (4) only

26. The pH value of a solution with [H+(aq)] being equal to 1.00  10−3 mol dm−3 is A. B. C. D.

3. 8. 11. 14.

28. Which of the following substances has a pH value below 7 at room conditions? A. B. C. D.

‘Milk of Magnesia’ Limewater Soap solution Vinegar

30. Which of the following indicators is used to measure pH of aqueous solutions accurately? A. B. C. D.

pH meter Universal indicator Methyl orange Litmus paper

*32. Arrange the following solutions in ascending order of pH values: (1) (2) (3) (4)

1 M KHCO3(aq) 1 M HNO3(aq) 1 M KOH(aq) 0.1 M KOH(aq)

A. B. C. D.

(1),(2),(3),(4) (2),(1),(4),(3) (2),(4),(3),(1) (3),(4),(1),(2)

Ch 14 Introduction of acid and alkalis / Ch 16 Indicator and pH / Ch 17 Strength / Ch 18 Salt and neutralization

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Topic 4 â&#x20AC;&#x201C; Acids and Bases (Part A) 33. The pH scale below shows the position of four aqueous solutions W, X, Y and Z of equal concentration. W 1

X 7

Y

Z 14

What could the aqueous solutions be? Ethanoic acid Potassium chloride Ammonia A. X Y Z B. Z Y X C. W X Y D. Y Z W

Sodium hydroxide W W Z X

34. Which of the following combinations for acid-base indicators is correct? Acid-base indicator Colour of the indicator Colour of the indicator in strongly acidic in strongly alkaline solutions solutions (1) Litmus Red Blue (2) Methyl orange Yellow Orange (3) Phenolphthalein Pink Colourless A. (1) only B. (3) only C. (1) and (2) only D. (1) and (3) only 35. The colours of the universal indicator in four sample solutions are summarized as follows: Solution Colour W Orange X Blue Y Green Z Red Which of the following is the correct descending order in pH values of the solutions? A. W, X, Y, Z B. X, Y, Z, W C. Z, W, Y, X D. X, Y, W, Z *36. The table below gives information about three indicators: Indicator Colour change Low pH to high pH Thymol blue Red to yellow Bromothymol blue Yellow to blue Phenolphthalein Colourless to pink

pH at which colour change takes place 3.0 6.5 9.0

If equal volumes of these three indicators were mixed, which colour would be observed at pH 4? A. Blue B. Green HOW can we change the pH of a solution? C. Orange (changing the concentration of H+) D. Yellow Ch 14 Introduction of acid and alkalis / Ch 16 Indicator and pH / Ch 17 Strength / Ch 18 Salt and neutralization

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Topic 4 – Acids and Bases (Part A)  Changing the pH of solution by dilution (稀釋, = adding water into it): Upon dilution: Change in pH upon dilution pH of an acid

pH of an alkali

Increases

Decreases

38. Calculate the pH of the following solutions: Given: pH = -log[H+] (a) 1M HCl

(b) 0.1M HCl

and pH + pOH = 14 (c) 1M NaOH

(d) 0.1M NaOH

37. Which of the following statements are correct? (1) Hydrochloric acid can have a pH value of zero. (2) pH paper contains more than one indicators. (3) The pH value of an acidic solution increases when water is added to it. A. (1) and (2) only B. (1) and (3) only C. (2) and (3) only D. (1), (2) and (3) *39. Solution A is an aqueous solution with pH 3 while solution B is an aqueous solution with pH 1. How does the [H+(aq)] in solution A compare with that in solution B? A. The [H+(aq)] in solution A is three times greater than the [H+(aq)] in solution B. B. The [H+(aq)] in solution A is one third of the [H+(aq)] in solution B. 1 C. The [H+(aq)] in solution A is of the 10 [H+(aq)] in solution B. 1 D. The [H+(aq)] in solution A is of the 100 [H+(aq)] in solution B.

 Changing the pH of solution by dissolving an oxide in water Dissolving a Gp. I or II metal oxide / hydroxides  pH increases

Dissolving some non-metal oxide / hydroxides  pH decreases

Dissolving CaO(s) and CO2(g) in water

40. Which of the following elements burns in air to form an oxide that gives a solution with a pH value smaller than 7 when shaken with water? A. B. C. D.

Sulphur Iron Zinc Hydrogen

41. A sample of gas was bubbled into pure water. The pH value of the solution slowly changed from 7 to 12. Which of the following gases could it be? A. B. C. D.

Carbon monoxide Nitrogen Calcium oxide Carbon dioxide

Ch 14 Introduction of acid and alkalis / Ch 16 Indicator and pH / Ch 17 Strength / Ch 18 Salt and neutralization

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Topic 4 – Acids and Bases (Part A)  Changing the pH of solution by adding a base Definition: Base is a compound which reacts with an acid to give salt and water only. a base can be: 1. Gp. I and II metal hydroxide e.g. NaOH, Mg(OH)2

Base

2. Gp. I and II metal oxide e.g. Na2O, CaO

44. Which of the following statements about all alkalis is/ are correct? (1) They must contain metal ions. (2) They produce hydroxide ions when dissolved in water. (3) Their aqueous solutions turn red litmus blue. A. (1) only B. (2) only C. (1) and (3) only D. (2) and (3) only

Alkali

Chemical reaction of acid 2 of 3: reaction between acid and bases

3. Ammonia solution NH3

Alkali is a kind of base which is soluble in water: e.g. KOH, NaOH, Ca(OH)2 and NH3

Neutralization is a chemical reaction between acid and base to give salt and water only.

Acid + Base  Salt + Water Write the following chemical equations:

Alkali =

45. (a) hydrochloric acid + sodium hydroxide 

OH-(aq)

(b) nitric acid + calcium hydroxide  Alkali: slippery feel / can turn red litmus paper to blue / taste bitter

42. Which of the following chemicals is/ are base(s)? (1) Sodium hydroxide (2) Magnesium hydroxide (3) Ammonia A. (1) and (2) only B. (1) and (3) only C. (2) and (3) only D. (1), (2) and (3)

(c) sulphuric acid + potassium hydroxide  Ionic equation:

H+(aq) + OH-(aq)  H2O(l)

46. (a) calcium oxide + hydrochloric acid  (b) sodium oxide + sulphuric acid 

43. Copper(II) oxide is a base. Calcium hydroxide is an alkali. Which of the following statements is correct for calcium hydroxide but not for copper(II) oxide? A. It contains oxygen. B. It is slightly soluble in water. C. It forms salts with acids. D. It reacts with nitrogen

47. (a) ammonia solution + hydrochloric acid  (b) ammonia solution + sulphuric acid 

Ch 14 Introduction of acid and alkalis / Ch 16 Indicator and pH / Ch 17 Strength / Ch 18 Salt and neutralization

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Topic 4 – Acids and Bases (Part A) 48. Which of the following equations best represents the reaction between dilute nitric acid and potassium hydroxide? A. 2H2 + O2  2H2O B. NO3 + K+  KNO3 C. H+ + OH  H2O D. H+ + NO3  HNO3

49. When dilute hydrochloric acid is added to iron(II) oxide,

*50. Which of the following is NOT a neutralization reaction? A. ZnO(s) + H2SO4(aq)  ZnSO4(aq) + H2O(l) B. Na2CO3(aq) + 2HNO3(aq)  2NaNO3(aq) + H2O(l) + CO2(g) C. H+(aq) + OH−(aq)  H2O(l) D. NH3(aq) + HCl(aq)  NH4Cl(aq)

*51. When sulphur dioxide is bubbled into a sodium hydroxide solution for a long time, the final product is A. Sodium sulphate B. Sodium sulphite C. Sodium hydrogencarbonate D. Sodium carbonate

Change in pH after neutralization (Recall) We can change the pH of a solution by:

by dilution (+ H2O) acid

alkali

pH 

pH 

 by dissolving an oxide into water

 by neutralization

metal oxide  alkaline

non-metal oxide  acidic

+ base

pH 

pH 

pH 

+ acid pH 

A. B. C. D.

iron and water are formed. iron(II) chloride and carbon dioxide are formed. iron(II) chloride and water are formed. only iron(II) chloride is formed.

a base can be: 1. Gp. I and II metal hydroxide e.g. NaOH, Mg(OH)2 2. Gp. I and II metal oxide e.g. Na2O, CaO 3. Ammonia solution NH3

an acid can be: HCl H2SO4 HNO3

H2CO3 CH3COOH H2SO3 H3PO4 Citric acid Oxalic acid

pH change during neutralization 

52. Dilute sulphuric acid has a pH value of 2. Which of the following substances, when added to dilute sulphuric acid, will increase its pH value? (1) Magnesium hydroxide (2) Iron(II) oxide (3) Ammonia A (1) and (2) only B (1) and (3) only C (2) and (3) only D (1), (2) and (3)

53. Which of the following substances can decrease the pH value of an ammonia solution? (1) Vinegar (2) Water (3) Solid citric acid A (1) and (2) only B (1) and (3) only C (2) and (3) only D (1), (2) and (3)

*54. q s t Solution p r 3 5 10 13 pH 7 Which of the following pairs of solutions will probably give a solution with pH same as that of solution r when they are mixed? (1) p and s (2) q and t (3) s and t A (1) and (2) only B (1) and (3) only C (2) and (3) only D (1), (2) and (3)

55. A hydrochloric acid solution has a pH value of 3. Which of the following substances would increase the pH value of the solution when mixed with it? (1) Dilute ammonia solution (2) Concentrated sulphuric acid (3) Water A. B. C. D.

(1) and (2) only (1) and (3) only (2) and (3) only (1), (2) and (3) During neutralization, pH of solution changes. TEMPERATURE of solution also changes!

Ch 14 Introduction of acid and alkalis / Ch 16 Indicator and pH / Ch 17 Strength / Ch 18 Salt and neutralization

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Topic 4 – Acids and Bases (Part A) Change in temperature during neutralization Neutralization is an exothermic reaction because heat

Compare the temperature rise:  dibasic > monobasic

 strong > weak*

Monobasic acid

Strong acid

is released. HCl

HNO3

CH3COOH

HCl

Dibasic acid H2SO4

H2SO3

56. In an experiment, 20 cm3 of 0.5 M nitric acid is added slowly into 10 cm3 of 1.0 M potassium hydroxide solution. Which of the following statements about the experiment is correct? A. The mixture does not conduct electricity at the end of the experiment. B. The pH value of the mixture increases. C. The temperature of the mixture increases. D. The concentration of nitrate ions in the mixture remains unchanged. [12DSE/MC#14] 58. Which of the following pairs of reactants would react to give out the largest amount of heat? A. 1 mole HCl and 1 mole of KOH B. 1 mole of H2SO4 and 2 mole KOH C. 1 mole (COOH)2 and 2 mole KOH D. 1 mole CH3COOH and 1 mole KOH

HNO3

H2SO3

Weak acid H2CO3

Tribasic acid H3PO4

H2SO4

Citric acid

H2CO3

H3PO4 CH3COOH

Citric acid

*because some heat is used for ionization of weak acid

57. Which of the following statements about the reaction of aqueous ammonia with sulphuric acid is correct? A. B. C. D.

The reaction is endothermic. A coloured solution is formed. Ammonia is produced. Ammonium sulphate is the product formed.

*60. Which of the following graphs represents the relationship between the temperature of the mixture and the volume of sodium hydroxide solution added when 1 M sodium hydroxide solution is added continuously to 25 cm3 of 1 M hydrochloric acid?

[03CE/MC#30] 59. 40 cm3 of 2 M hydrochloride acid was mixed with 40 cm3 of 2 M sodium hydroxide solution in a polystyrene cup and the maximum rise in temperature was recorded. Which of the following pairs of solutions, upon mixing, would produce a similar rise in temperature? A. 40 cm3 of 2M ethanoic acid and 40 cm3 of 2 M potassium hydroxide solution B. 40 cm3 of 2M ethanoic acid and 40 cm3 of 2 M ammonia solution C. 40 cm3 of 2M nitric acid and 40 cm3 of 2 M potassium hydroxide solution D. 40 cm3 of 2M nitric acid and 40 cm3 of 2 M ammonia solution

* excess alkali added will absorb heat from the reaction mixture

Ch 14 Introduction of acid and alkalis / Ch 16 Indicator and pH / Ch 17 Strength / Ch 18 Salt and neutralization

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Topic 4 – Acids and Bases (Part A) Applications of neutralization Daily life

Industry or others Slaked lime, Ca(OH)2 / Alum Too acidic soil Too alkaline soil

Milk of magnesia, Mg(OH)2

Neutralize by adding slaked lime, Ca(OH)2

 *Antacid: Neutralize excess acid in stomach

Neutralize by adding alum KAl(SO4)2 . 12H2O acid salt, will learn later

*Some antacids may use CaCO3(s), but it will produce uncomfortable feelings as CO2(g) is produced in stomah.

Sodium hydrogencarbonate / Vinegar  Treat the acid / alkali from insect stings Acidic stings by ant / bee

Alkaline stings by wasp

Ammonia / Nitric acid  Make fertilizer

Another fertilizer: 2NH3 + H2SO4  (NH4)2SO4

calcium oxide, CaO Neutralize acidic gas pollutants (e.g. SO2) by a scrubber in power stations

Industrial effluent treatment:

Treat by weak alkaline solution e.g. NaHCO3(aq)

Neutralize by weak acid e.g. CH3COOH(aq)

61. Which of the following substances is commonly used to reduce soil acidity? A. B. C. D.

Ammonium sulphate Sodium chloride Magnesium nitrate Calcium hydroxide

Acidic effluent From electroplating industry Neutralize by Ca(OH)2 / react with CO32-

Alkaline effluent From dyeing industry Neutralize by H2SO4

62. Which of the following is NOT used to neutralize the acidic liquid waste from industries? A. Sodium hydroxide B. Sodium carbonate C. Calcium carbonate D. Calcium hydroxide

Ch 14 Introduction of acid and alkalis / Ch 16 Indicator and pH / Ch 17 Strength / Ch 18 Salt and neutralization

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Topic 4 – Acids and Bases (Part A) 63. Which of the following chemicals is/are used to neutralize the excess acid in stomach? (1) Mg(OH)2 (2) Al(OH)3 (3) NaOH A. B. C. D.

(1) and (2) only (1) and (3) only (2) and (3) only (1), (2) and (3)

65. Which of the following is NOT an application of neutralization? A B C D

Relieving stomach aches Relieving insect stings Treating acidic soils Using ammonia to remove oil stain

64. Lime can be used to reduce the acidity of soil. It is because A. lime absorbs acid. B. lime gives alkaline products when dissolved in water. C. lime reacts with soil to form alkaline products. D. lime prevents acidic substances dissolving in soil.

66. Why calcium carbonate is rarely used as the active ingredient in antacids? A Calcium carbonate reacts with hydrochloric acid in stomach to produce carbon dioxide which builds up pressure in stomach. B Calcium carbonate attacks the wall of stomach. C Calcium carbonate cannot neutralize hydrochloric acid in stomach. D Calcium carbonate is carcinogenic.

Other applications of acid:

Rust remover: contains weak acid which will react with Rust = Fe2O3 . xH2O

metal oxide (rust) to form salt and water

Fizzy drink tablets contain a solid acid and sodium hydrogencarbonate. There is effervescence when the tablets are dissolved in water. Write an ionic equation for the change:

H+(aq) + HCO3-(aq)  CO2(g) + H2O(l)

Baking powder (泡打粉) is either sodium hydrogencarbonate or a mixture of sodium hydrogencarbonate + a *solid acid. Sodium hydrogencarbonate decomposes (分解) on heating to give #carbon dioxide gas:

Preparation of CO2 in lab and its properties 

 eggs + vinegar = ‘naked’ eggs

* The baking powder should be stored in a dry place because the acid will react with hydrogencarbonate ions in the presence of water. # Carbon dioxide makes cakes rise and spongy.

Ch 14 Introduction of acid and alkalis / Ch 16 Indicator and pH / Ch 17 Strength / Ch 18 Salt and neutralization

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Topic 4 â&#x20AC;&#x201C; Acids and Bases (Part A) 67. Some brown solid deposits are sometimes found on iron woks if the woks are not thoroughly dried after washing. These brown substances cannot be washed away with water but can be removed with vinegar. Rust: brown solid deposits

Fe2O3 . xH2O Hydrated iron (III) oxide

iron wok

(a) What are those brown deposits? Under what conditions are they formed? [2 marks]

(b) Write an equation to show how these brown deposits can be removed by vinegar. [1 mark]

(c) Name the type of reaction taking place in (b). [1 mark]

(d) With the help of an equation, explain why cooks usually do not use iron cooking utensils for cooking food with vinegar. [2 mars]

(e) Give the name and the formula of the salt formed when vinegar and baking powder (containing sodium hydrogencarbonate) are mixed. [2 marks]

Ch 14 Introduction of acid and alkalis / Ch 16 Indicator and pH / Ch 17 Strength / Ch 18 Salt and neutralization

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Topic 4 – Acids and Bases (Part A) Chemical reaction of acid 3 of 3: reaction between acid and carbonates,

CO32- / hydrogencarbonates, HCO3-

Carbonate + Acid  Salt + Carbon dioxide gas + Water Hydrogencarbonate + Acid  Salt + Carbon dioxide gas + Water [99CE/2(a)/2 marks] 68. For following experiment, state ONE observable change and write a chemical equation for the reaction involved. Dilute nitric acid is added to magnesium carbonate powder in a beaker. Observable change: Chemical equation: 69. For each of the following reactions (if any), write down (i) a full equation for the reaction. (ii) an ionic equation for the reaction.

(a) Sodium carbonate solution is added into concentrated hydrochloric acid. Full: Ionic: (b) *Solid calcium carbonate + dilute hydrochloric acid Full: Ionic:

Other applications of alkali: In electroplating industry, its effluent may contain heavy metal ions.These heavy metal ions may cause the death of Glass cleaner: Oven cleaner / Drainage cleaner: marine lives. NH3(aq)

NaOH(aq)

How to remove?

(ppt. + filtration)

Add NaOH(aq) Metal ions form precipitate with hydroxide ions, then filter off.

For example,

Cu2+(aq) + 2OH-(aq)  Cu(OH)2(s) *Most metal hydroxides are insoluble in water Ch 14 Introduction of acid and alkalis / Ch 16 Indicator and pH / Ch 17 Strength / Ch 18 Salt and neutralization

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Topic 4 – Acids and Bases (Part A) Mx+(aq) + xOH-(aq)  M(OH)x(s) (except K+, Na+ and Ca2+) How to Metal cation Observation / Chemical equation test Potassium ion K+ No observable change

Sodium ion Na+ Calcium ion Ca2+

+ NaOH(aq): White precipitate is formed Ca2+(aq) + 2OH-(aq)  Ca(OH)2(s)

Magnesium ion Mg2+

White precipitate is formed Mg2+(aq) + 2OH-(aq)  Mg(OH)2(s)

Aluminum ion Al3+

White precipitate is formed Al3+(aq) + 3OH-(aq)  Al(OH)3(s) White precipitate re-dissolves in excess sodium hydroxide solution to give a colorless solution

Lead(II) ion Pb2+

White precipitate is formed Pb2+(aq) + 2OH-(aq)  Pb(OH)2(s) White precipitate re-dissolves in excess sodium hydroxide solution to give a colorless solution

Add sodium hydroxide or ammonia solution

Zinc ion Zn2+

White precipitate is formed Zn2+(aq) + 2OH-(aq)  Zn(OH)2(s) White precipitate re-dissolves in excess sodium hydroxide / ammonia solution to give a colorless solution

Copper (II) ion Cu2+

Blue precipitate is formed Cu2+(aq) + 2OH-(aq)  Cu(OH)2(s) Blue precipitate re-dissolves in excess ammonia solution to give a deep blue solution

Iron (II) ion Fe2+

Dirty-green precipitate is formed Fe2+(aq) + 2OH-(aq)  Fe(OH)2(s)

Iron (III) ion Fe3+

Brown precipitate is formed Fe3+(aq) + 3OH-(aq)  Fe(OH)3(s)

Re-dissolve in excess NaOH(aq): Al(OH)3(s), Pb(OH)2(s) and Zn(OH)2(s) ‘

又叻又醒就攞A’

Re-dissolve in excess NH3(aq): Zn(OH)2(s), Cu(OH)2(s) and AgOH(s) ‘

Ammonium ion

NH4+

Warm with sodium hydroxide solution

少少醒就攞C’

A pungent gas produced which turns wet red litmus paper blue NH4+(aq) + OH-(aq)  NH3(g) + H2O(l)

Ch 14 Introduction of acid and alkalis / Ch 16 Indicator and pH / Ch 17 Strength / Ch 18 Salt and neutralization

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Topic 4 â&#x20AC;&#x201C; Acids and Bases (Part A) 70. Which of the following aqueous solutions will give a coloured precipitate when mixed with ammonia solution? A. Magnesium nitrate B. Iron(III) sulphate C. Sodium hydroxide D. Zinc chloride

71. Which of the following combinations is INCORRECT?

72. Which of the following ions when treated with excess aqueous ammonia, gives a clear solution without any precipitates? A. Fe2+(aq) B. Al3+(aq) C. Cu2+(aq) D. Pb2+(aq)

[06CE/MC#7] 73. Compound X is soluble in water. Addition of sodium hydroxide solution to a solution of X gives a white precipitate. The precipitate does not dissolve upon the addition of excess alkali. X may be

Metal hydroxides Copper(II) hydroxide Iron(II) hydroxide Magnesium hydroxide Lead(II) hydroxide

A. B. C. D.

A. B. C. D.

Colour Blue Yellow White White

MgCl2 ZnCl2 FeSO4 (NH4)2SO4

*[06CE/MC#22] 74. Which of the following processes is/are application(s) of neutralization? (1) using scrubbers to remove sulphur dioxide from flue gas in a power station (2) using catalytic converters to remove nitrogen oxides in car exhaust (3) using sodium hydroxide solution to remove copper(II) ions in industrial waste water A. B. C. D.

(1) only (2) only (1) and (3) only (2) and (3) only

[01CE/2(b)/2 marks] 75. For the following experiment, state an expected observation and write a chemical equation for the reaction involved. Adding sodium hydroxide solution to iron(II) sulphate solution Observable change: Chemical equation:

Ch 14 Introduction of acid and alkalis / Ch 16 Indicator and pH / Ch 17 Strength / Ch 18 Salt and neutralization

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Topic 4 â&#x20AC;&#x201C; Acids and Bases (Part A) As ammonium compound reacts with alkali to give ammonia gas, we can prepare ammonia gas in laboratory with the following set-up:

Drying agents, e.g. anhydrous calcium chloride and concentrated sulphuric acid, cannot be used to dry ammonia as they will react with ammonia. Note: The boiling tube is tilted downwards to prevent the condensed water produced from flowing back which will crack the boiling tube. Ammonia is less dense than air and is thus collected by upward delivery (downward displacement of air). It has pungent smell and vey soluble in water. Ammonia gas is the only gas which turns moist red litmus paper blue. This is a test for ammonia gas. 76. Which of the following gases is formed when ammonium sulphate is warmed with aqueous potassium hydroxide? A. Carbon dioxide B. Sulphur dioxide C. Nitrogen D. Ammonia

77. Which of the following is NOT a property of ammonia? A. It is very soluble in water. B. It has an pungent smell. C. It is heavier than air. D. It is colourless.

Ch 14 Introduction of acid and alkalis / Ch 16 Indicator and pH / Ch 17 Strength / Ch 18 Salt and neutralization

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Topic 4 â&#x20AC;&#x201C; Acids and Bases (Part A) 78. Ammonia gas CANNOT turn dry red litmus paper blue because A. it is an acid. B. it is neutral. C. it contains no OHď&#x20AC;­ ion. D. it contains no H+ ion.

79. Which of the following substances will NOT react with sodium hydroxide solution? A. Ammonium sulphate B. Iron(III) nitrate C. Nitric acid D. Copper

80. Which of the following statements about an ammonia solution is/ are correct?

[04CE/MC#20] 81. Which of the following statements concerning aqueous ammonia is correct?

(1) It has a pH value greater than 7. (2) Hydroxide ion concentration is higher than hydrogen ion concentration. (3) It has pungent smell. A. B. C. D.

(1) and (2) only (1) and (3) only (2) and (3) only (1), (2) and (3)

[00CE/MC#29] 82. Which of the following compounds would react with ammonium chloride on heating? A. B. C. D.

concentrated nitric acid concentrated hydrochloride acid sodium hydroxide solution magnesium sulphate solution

A. It contains both ammonia molecules and molecules and ammonium ions. B. It is commonly used as the active ingredient in toilet cleaners. C. It reacts with iron(III) sulphate solution to give a green precipitate. D. It gives a colourless solution with phenolphthalein. [10CE/MC#20] 83. A mixture of (NH4)2SO4(aq) and MgSO4(aq) is heated with excess NaOH(aq). Which of the following observation is correct? A. No pungent gas is evolved and no precipitation is formed. B. No pungent gas is evolved but a white precipitate is formed. C. A pungent gas is evolved but no precipitate is formed. D. A pungent gas is evolved and a white precipitate is formed.

[10CE/2(a)(ii)/2 marks] 84. Ammonium dichromate solution, (NH4)2Cr2O7(aq), suggest a chemical test to sow the solution contains ammonium ions. State the expected observation. Chemical test:

Observation:

Ch 14 Introduction of acid and alkalis / Ch 16 Indicator and pH / Ch 17 Strength / Ch 18 Salt and neutralization

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Topic 4 â&#x20AC;&#x201C; Acids and Bases (Part A) [03CE/6(a)(i)-(iii)/6 marks] 85. Ammonia gas can be prepared by heating a mixture of ammonium chloride and calcium oxide in the set-up shown below:

(i)

The reaction of ammonium chloride with calcium oxide also gives calcium chloride as a product. Write the chemical equation for the reaction of ammonium chloride with calcium oxide.

(ii) Why is it necessary to clamp the test tube with its mouth pointing downwards as shown?

(iii) Decide which of the following set-ups, (I), (II) or (III), should be connected to the delivery tube to collect the ammonia gas produced. Explain your answer.

Ch 14 Introduction of acid and alkalis / Ch 16 Indicator and pH / Ch 17 Strength / Ch 18 Salt and neutralization

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Topic 4 â&#x20AC;&#x201C; Acids and Bases (Part A) [12DSE/paper1/7(a-(c))/3 marks] *86.

(a)

Write an ionic equation for the reaction between NH4NO3 and KOH.

(b)

Suggest the potential hazard of one of the chemicals used.

(c)

Given that ammonia is very soluble in water, state the advantage of using an inverted funnel.

Ch 14 Introduction of acid and alkalis / Ch 16 Indicator and pH / Ch 17 Strength / Ch 18 Salt and neutralization

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Topic 4 – Acids and Bases (Part A) Salt preparation Cation Formula from…

Salt name Silver chloride Lead(II) sulphate Calcium sulphate

Ag+

Sodium chloride Potassium nitrate Sodium sulphate

RULE 1 RULE 2 RULE 3

SO42-

Ca2+

SO42NaOH(aq)

Cl-

K+

NO3-

Na+

SO42excess CaO(s)

Ca2+

Ammonium chloride

Cl-

Pb2+

Na+

Calcium chloride Copper(II) nitrate Zinc sulphate

AgNO3(aq)

Anion Formula from…

Cl-

Cu2+

NO3-

Zn2+

SO42-

NH4+

Cl-

Nature of salt

NaCl(aq)

Normal salt

HCl(aq)

HCl(aq)

All insoluble salts: XY(s) ‘precipitation method’ X nitrate(aq) + sodium Y(aq) ‘titration method’ All group I salts: from a strong acid + a strong alkali Other metal salt: excess metal oxide / hydroxide / carbonate + acid

OTHERS ammonium salt: ammonia + acid

Formula of salt

Information 4 Neutralization

Nature of salt

SA + SB SA + WB WA + SB

Neutral salt (pH = 7) Acidic salt (pH < 7) Alkaline salt (pH > 7)

S = strong; W= weak; A = acid; B = base Information 2

Compound

Information 1 Strong acid HCl

H2SO4

Strong alkali

HNO3

H2SO3

NaOH

KOH

Halide XSulphate SO42Carbonate CO32-

Information 3 Oxide

Hydroxide

Carbonate

O2-

OH-

CO32-

Oxide O2-and hydroxide OH-

Solubility in water All are soluble except AgX and PbX2 All are soluble except CaSO4, PbSO4 and BaSO4 All are insoluble except Na2CO3, K2CO3 and (NH4)2CO3 All are insoluble except K2O, Na2O, KOH and NaOH. CaO and Ca(OH)2 are slightly soluble in water

Ch 14 Introduction of acid and alkalis / Ch 16 Indicator and pH / Ch 17 Strength / Ch 18 Salt and neutralization

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Topic 4 – Acids and Bases (Part A) 87. Which of the following methods is best for preparing sodium nitrate?

88. Which of the following salts is best prepared by titration method?

A. B. C. D.

A. B. C. D.

Add sodium sulphate solution to nitric acid. Add sodium to nitric acid. Add sodium hydroxide solution to nitric acid. Add sodium to zinc nitrate solution.

Copper(II) chloride Iron(II) sulphate Zinc sulphate Potasium chloride

89. Which of the following substances should NOT be used with hydrochloric acid to prepare magnesium chloride?

90. Which of the following salts could be obtained as an insoluble product from the reaction between two aqueous salts?

A. B. C. D.

A. B. C. D.

Magnesium hydroxide Magnesium nitrate Magnesium carbonate Magnesium oxide

Iron(II) sulphate Copper(II) nitrate Calcium sulphate Magnesium chloride

91. Which of the following salts can be prepared directly by precipitation method?

92. Which of the following reactions CANNOT be used to prepare zinc sulphate?

A. B. C. D.

A. B. C. D.

PbSO4 K2CO3 Ca(NO3)2 NH4Cl

93. Which of the following equations represents a correct way of preparing the salt underlined? A. B. C. D.

Mg(OH)2 + Na2SO4  MgSO4 + 2NaOH NH3 + HNO3  NH4NO3 Cu + H2SO4  CuSO4 + H2 AgCl + NaNO3  NaCl + AgNO3

zinc + dilute sulphuric acid zinc oxide + dilute sulphuric acid zinc carbonate + dilute sulphuric acid zinc nitrate + dilute sulphuric acid

94. Which of the following statements about salts is INCORRECT? A. Salts can be made by reacting acids with metal oxides. B. Salts are ionic compounds. C. Salts can be made by neutralizing acids with alkalis. D. Salts must be neutral.

[12DSE/MC#2] 95.

Ch 14 Introduction of acid and alkalis / Ch 16 Indicator and pH / Ch 17 Strength / Ch 18 Salt and neutralization

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Topic 4 â&#x20AC;&#x201C; Acids and Bases (Part A) [07CE/MC#38] 96. Which of the following methods is most suitable for preparing a sample of lead(II) sulphate? A. B. C. D.

adding lead to dilute sulphuric acid adding lead to copper(II) sulphate solution adding lead(II) oxide to dilute sulphuric acid adding lead(II) nitrate solution to dilute sulphuric acid

[10CE/MC#40] 97.

Ch 14 Introduction of acid and alkalis / Ch 16 Indicator and pH / Ch 17 Strength / Ch 18 Salt and neutralization

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Topic 4 – Acids and Bases (Part A) Preparation of insoluble salt (e.g. silver chloride) by precipitation of soluble reactants (1)

Mix sodium chloride solution and silver nitrate solution. AgNO3(aq) + NaCl(aq)  AgCl(s) + NaNO3(aq) (Ionic equation: Ag+(aq) + Cl-(aq)  AgCl(s))

(2)

Filter off the precipitate. Wash the precipitate with distilled water and dry the precipitate with filter paper.

[12DSE/paper1/6/4 marks] 98. Outline the steps in preparing solid lead(II) sulphate from solide lead(II) nitrate. You have to state the additional chemical reagents that are required, but need NOT mention the apparatus involved.

_________________________________________________________________________________________ _________________________________________________________________________________________ _________________________________________________________________________________________ _________________________________________________________________________________________ _________________________________________________________________________________________

Ch 14 Introduction of acid and alkalis / Ch 16 Indicator and pH / Ch 17 Strength / Ch 18 Salt and neutralization

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Topic 4 â&#x20AC;&#x201C; Acids and Bases (Part A) 99. Lead(II) chloride can be prepared by the following precipitation method: Lead(II) nitrate solution is added to an excess of sodium chloride solution. The precipitate obtained is filtered, washed and then heated.

i) Write an ionic equation for the reaction involved.

ii) Explain why it is necessary to wash the precipitate.

iii) Explain why it is necessary to heat the precipitate.

iv) Explain why the precipitation method is suitable for the preparation of lead(II) chloride.

Ch 14 Introduction of acid and alkalis / Ch 16 Indicator and pH / Ch 17 Strength / Ch 18 Salt and neutralization

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Topic 4 â&#x20AC;&#x201C; Acids and Bases (Part A) Preparation of soluble salt (e.g. copper(II) sulphate) from acid and insoluble base/ insoluble carbonates/ metals i)

Add excess copper(II) oxide to dilute sulphuric acid. Heat the solution if necessary. CuO(s) + H2SO4(aq)

ii)

ď&#x192; CuSO4(aq) + H2O(l)

Filter the mixture after the reaction has completed to remove excess copper(II) oxide. The filtrate is copper(II) sulphate solution. Note: Excess CuO is used to ensure all sulphuric acid is used up.

iii)

Warm the solution in an evaporating dish until a saturated (or concentrated) solution is obtained Note: If the copper(ll) sulphate solution is not concentrated enough, no crystals will be obtained even after cooling.

iv)

Cool the solution slowly. Large crystals are obtained.

v)

Filter off the crystals. Wash them with small amount of cold distilled water and dry the crystals with filter paper.

Ch 14 Introduction of acid and alkalis / Ch 16 Indicator and pH / Ch 17 Strength / Ch 18 Salt and neutralization

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Topic 4 â&#x20AC;&#x201C; Acids and Bases (Part A) [08CE/11/9 marks] 100. Copper(II) sulphate crystals (CuSO4ď&#x201A;ˇ5H2O) can be prepared in a laboratory by the following steps. Step 1: Add excess copper(II) oxide to dilute sulphuric acid and warm the mixture. Step 2: Remove the remaining copper(II) oxide from the solution obtained. Step 3: Evaporate the solution until it becomes saturated. Step 4: All the saturated solution to cool down to obtain copper(II) sulphate crystals. Step 5: Separate the crystals from the saturated solution. Step 6: Dry the crystals obtained. (a)

(i)

For step 1, (1)

write a chemical equation for the reaction involved, and

(2)

explain why copper(II) oxide should be in excess.

(ii)

For step 2, suggest how to remove the remaining copper(II) oxide.

(iii)

For step 4, explain why crystals would be obtained when the saturated solution is allowed to cool down.

(iv)

For step 6, (1)

explain why the crystals obtained should not be dried by heating, and

(2)

suggest an appropriate method to dry the crystals.

(6 marks) (b)

A student finally obtained 16.2 g dry copper(II) sulphate crystals through the above steps by reacting 150 cm3 of 1.0 M sulphuric acid with excess copper(II) oxide. (i)

Calculate the number of moles of copper(II) sulphate in the solution obtained in Step 1.

(ii)

Calculate the number of moles of copper(II) sulphate crystals finally obtained.

(iii)

Assuming the student dried the crystals in Step 6 by an appropriate method, comment on whether there should be any difference between the answers obtained in (i) and (ii) above.

(3 marks)

Ch 14 Introduction of acid and alkalis / Ch 16 Indicator and pH / Ch 17 Strength / Ch 18 Salt and neutralization

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Topic 4 â&#x20AC;&#x201C; Acids and Bases (Part A) Preparation of soluble salt (e.g. ammonium sulphate) from acid and alkali / soluble carbonate i)

Titrate a known volume, Vl, of ammonia solution with dilute sulphuric acid (in the presence of pH indicator) until end-point is reached. Record the volume, V2, of H2SO4 used. 2NH3(aq) + H2SO4(aq) ď&#x192; (NH4)2SO4(aq)

ii)

Mix another V1 of ammonia solution and V2 of dilute sulphuric acid without adding any indicator (this is to prevent the indicator from contaminating the salt solution formed). Note: If the concentrations of NH3(aq) and H2SO4(aq) are known, the step below should be used instead of steps i & ii: Mix NH3(aq) and H2SO4(aq) in mole ratio of 2: 1.

iii)

Warm the solution in an evaporating dish until a saturated (or concentrated) solution is obtained.

iv)

Cool the solution slowly. Large crystals are obtained.

v)

Filter off the crystals. Wash them with small amount of cold distilled water and dry the crystals with filter paper.

101. Potassium sulphate can be prepared by reacting an alkali with dilute sulphuric acid using titration method. i) Name an alkali which can be used to make potassium sulphate.

ii) Explain why titration method is suitable for the preparation of potassium sulphate.

iii) Can potassium sulphate be prepared by mixing potassium chloride solution and sodium sulphate solution? Explain briefly.

Ch 14 Introduction of acid and alkalis / Ch 16 Indicator and pH / Ch 17 Strength / Ch 18 Salt and neutralization

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Topic 4 – Acids and Bases (Part A) Corrosive nature of concentrated acid 

Concentrated acids are usually highly corrosive. Hence, wear safety glasses and plastic gloves when handling them.

Properties of concentrated acids: Concentrated

Hazard

acid

warning labels

HCl

Remarks  

(about 11M)   H2SO4 (about 18M)

HNO3 (about 16M)

It gives out white fumes in air It reacts (e.g. with emtals) in a similar way as dil. HCl(aq) but at a faster rate It is highly corrosive due to high concentration of H+(aq) It can burn holes on paper and clothes. Its corrosive nature is due to its oxidizing property and dehydrating property.

Its corrosive nature is due to its oxidizing property.

If concentrated acid is spilled onto skin or gets into eye, wash it with a lot of water.

We should not use alkali to neutralize the acid spilled onto skin because a lot of heat is evolved in neutralization and thus causes burning of skin.

Ch 14 Introduction of acid and alkalis / Ch 16 Indicator and pH / Ch 17 Strength / Ch 18 Salt and neutralization

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Topic 4 – Acids and Bases (Part A) 

To dilute the acid is

concentrated acid,

slowly added to a large amount of water with

stirring. If water is added to concentrated acid, a lot of heat will evolve which will cause the acid to splash out.

[00CE/8(c)(ii)/2 marks] 102. State whether the following statement is true or false. Explain your answer. ‘When concentrated sulphuric acid is diluted, water should be added slowly to the acid.‘

[0CE/3(c)/2 marks] 103. A student proposed the following methods to accomplish the task below. The proposed method were all considered inappropriate. Task : To dilute concentrated sulphuric acid with water. Proposed method : Add water to concentrated sulphuric acid and stir the mixture. (i)

State ONE reason why the method is inappropriate.

(ii)

Suggest an appropriate method to accomplish the task.

Ch 14 Introduction of acid and alkalis / Ch 16 Indicator and pH / Ch 17 Strength / Ch 18 Salt and neutralization

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Page 33


Topic 4 â&#x20AC;&#x201C; Acids and Bases (Part A) Special case : conc. H2SO4 reacts with CaCO3:

1 ________ is formed

3 Insoluble layer prevents ___________________________

which is _________

2

in water

___________________________ Finally, bubbling stops. 4

Any metal(s) will react with acid(s) similarly?

Ch 14 Introduction of acid and alkalis / Ch 16 Indicator and pH / Ch 17 Strength / Ch 18 Salt and neutralization

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Topic 4 â&#x20AC;&#x201C; Acids and Bases (Part A) Challenging question: http://hksciblog.edublogs.org/?p=2653 Mr. Tsui wants to carry out a displacement reaction. He has put a Mg ribbon into copper(II) sulphate solution. Some gas bubbles are produced on Mg ribbon immediately. After three days, he found that some brown solids are formed on the Mg ribbon. He expected that the Mg ribbon will be dissolved but the Mg ribbon is still there, hence, he has taken a picture of it as shown. (a)

Write an ionic equation for the displacement reaction.

(b)

Why do Mr. Tsui expect that the Mg ribbon will dissolve?

(c)

Write a chemical reaction for the gas bubble produced. (hint: Mg is a reactive metal that can react with water)

(d)

What is that unknown layer?

(e)

Suggest one method to remove that unknown layer.

(f)

Write a chemical equation for (c).

Ch 14 Introduction of acid and alkalis / Ch 16 Indicator and pH / Ch 17 Strength / Ch 18 Salt and neutralization

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Topic 4 – Acids and Bases (Part A)

Answer: 1.

2.

(a)

Zn(s) + H2SO4(aq)  ZnSO4(aq) + H2(g)

(b)

Zn(s) + 2H+(aq)  Zn2+(aq) + H2(g)

(a)

Fe(s) + 2HCl(aq)  FeCl2(aq) + H2(g)

(b)

Fe(s) + 2H+(aq)  Fe2+(aq) + H2(g)

3.

4.

Each H2SO4 molecule is ionized into water to produce two hydrogen ions and one sulphate ion. Hydrogen ions react with zinc metal to produce hydrogen gas.

5.

water / ionize / hydrogen ions

6.

1M HNO3 will give bubbles at a faster rate. Because HNO3 is a strong acid but carbonic acid is a weak acid, HNO3 can completely ionized into water. HNO3 contains higher concentration of hydrogen ions than carbonic acid.

7.

0.1M H2SO4 will give bubbles at a faster rate. Because H2SO4 is a dibasic acid but HNO3 is a monobasic acid, H2SO4 contains higher concentration of hydrogen ions than HNO3.

8.

A.

Carbonic acid is a weak acid but all other acids are strong acids.

H2CO3 can only slightly ionize in water. Therefore, it contains less mobile ions than other acids. 9.

A

10.

A

mobile ion, NOT mobile electron in solution

11.

Ch 14 Introduction of acid and alkalis / Ch 16 Indicator and pH / Ch 17 Strength / Ch 18 Salt and neutralization

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Page 36


Topic 4 – Acids and Bases (Part A) 12.

C

13.

D

14.

B

15.

B

16.

A

17.

C

18.

A

19.

B

20.

C

21.

D

22.

pH 0 - 14

23.

X<W<Y<Z

24.

Because HCl is a strong acid but CH3COOH is a weak acid. HCl can completely ionize in water. HCl has a higher concentration of hydrogen ions. Therefore, it has a lower pH.

25.

B

26.

A

27.

A

28.

D

29.

B

30.

A

31.

C

32.

B

33.

C

34.

A

35.

D

36.

D

37.

D

38.

(a)

pH = 0

(b)

pH = 14

(c)

pH = 1

(d)

pH = 13 C

42.

D

39.

D

40.

A

43.

B

44.

D

45.

(a)

HCl(aq) + NaOH(aq)  NaCl(aq) + H2O(l)

(b)

2HNO3(aq) + Ca(OH)2(aq)  Ca(NO3)2(aq) + 2H2O(l)

(c)

H2SO4(aq) + 2KOH(aq)  K2SO4(aq) + 2H2O(l)

(a)

CaO(s) + 2HCl(aq)  CaCl2(aq) + H2O(l)

(b)

Na2O(s) + H2SO4(aq)  Na2SO4(aq) + H2O(l)

(a)

NH3(aq) + HCl(aq)  NH4Cl(aq)

(b)

2NH3(aq) + H2SO4(aq)  (NH4)2SO4(aq)

46.

47.

41.

48.

C

49.

C

50.

B

51.

B

52.

D

53.

D

54.

A

55.

B

56.

C

57.

D

58.

B

59.

C

60.

C

61.

D

62.

A

63.

A

64.

B

65.

D

66.

A

Ch 14 Introduction of acid and alkalis / Ch 16 Indicator and pH / Ch 17 Strength / Ch 18 Salt and neutralization

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Page 37


Topic 4 – Acids and Bases (Part A) 67.

(a)

Rust (hydrated iron(III) oxide). [1]

It is formed from the oxidation of iron in the presence of water and air. [1] (b)

Fe2O3(s) + 6CH3COOH(aq)  2(CH3COO)3Fe(aq) + 3H2O(l) [1]

(c)

Neutralization [1]

(d)

Iron dissolves slowly in vinegar (acidic solution). [1] Fe(s) + 2CH3COOH(aq)  (CH3COO)2Fe(aq) + H2(g) [1]

(e)

Sodium ethanoate, CH3COONa [1]+[1]

68.

69. (a) (i)

Na2CO3(aq) + 2HCl(aq)  2NaCl(aq) + CO2(g) + H2O(l)

(ii) CO32-(aq) + 2H+(aq)  H2O(l) + CO2(g) (b) (i)

CaCO3(s) + 2HCl(aq)  CaCl2(aq) + CO2(g) + H2O(l)

(ii) CaCO3(s) + 2H+(aq)  Ca2+(aq) + CO2(g) + H2O(l) 70. B

71.

B

76. D

77.

C

81. B

82.

C

72.

C

73.

A

78.

C

79.

D

80.

83.

D

74. A

75. D

84.

Ch 14 Introduction of acid and alkalis / Ch 16 Indicator and pH / Ch 17 Strength / Ch 18 Salt and neutralization

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Page 38


Topic 4 â&#x20AC;&#x201C; Acids and Bases (Part A) 85.

86.

87. C

88.

D

89.

B

90.

C

91. A

92.

D

93.

B

94.

D

95. D

96.

D

97.

C

98.

Ch 14 Introduction of acid and alkalis / Ch 16 Indicator and pH / Ch 17 Strength / Ch 18 Salt and neutralization

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Page 39


Topic 4 – Acids and Bases (Part A) 99. i) Pb2+(aq) + 2Cl-(aq)  PbCl2(s) ii) To remove any impurities (e.g. excess NaCl) adhering to the lead(II) chloride. iii) To remove any water adhering to the lead(II) chloride. iv) The product (PbCl2) is insoluble in water while the reactants (Pb(NO3)2 and NaCl) are soluble 100.

Ch 14 Introduction of acid and alkalis / Ch 16 Indicator and pH / Ch 17 Strength / Ch 18 Salt and neutralization

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Page 40


Topic 4 â&#x20AC;&#x201C; Acids and Bases (Part A) 101. i) Potassium hydroxide solution ii) The reactants (KOH and H2SO4) and the product (K2SO4) are soluble. iii) No. The resulting solution contains four mobile ions: K+(aq), Na+(aq), Cl-(aq) and SO42+(aq). It is not possible to extract K+(aq) and SO42-(aq) only in the presence of other ions. 102.

103.

Ch 14 Introduction of acid and alkalis / Ch 16 Indicator and pH / Ch 17 Strength / Ch 18 Salt and neutralization

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Page 41


Topic 4 – Acids and Bases (Part A) Summary:

Action on

wet blue

Turns

red

litmus paper Conduct electricity

Electrical conductivity

because acids contain

mobile ions

Metal + dilute acid  Salt + hydrogen gas e.g. Zn(s) + 2HCl(aq)  ZnCl2(aq) + H2(g)

Reaction with

metals above Cu in the metal reactivity series *

Reaction with

metal oxides

O2-

Metal oxide + dilute acid  salt + water e.g. MgO(s) + 2HCl(aq)  MgCl2(aq) + H2O(l)

Reaction with

metal OHhydroxides Reaction with metal carbonates CO32metal hydrogen- HCO3carbonates Reaction with

Metal hydroxide + dilute acid  salt + water e.g. NaOH(aq) + HCl(aq)  NaCl(aq) + H2O(l)

Metal carbonate + dilute acid 

salt + water + carbon dioxide

e.g. Na2CO3(aq) + 2HCl(aq)  2NaCl(aq) + H2O(l) + CO2(g) Metal hydrogencarbonate + dilute acid 

salt + water + carbon dioxide

e.g. NaHCO3(aq) + HCl(aq)  NaCl(aq) + H2O(l) + CO2(g)

Ch 14 Introduction of acid and alkalis / Ch 16 Indicator and pH / Ch 17 Strength / Ch 18 Salt and neutralization

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Page 42


Topic 4 â&#x20AC;&#x201C; Acids and Bases (Part A)

Ch 14 Introduction of acid and alkalis / Ch 16 Indicator and pH / Ch 17 Strength / Ch 18 Salt and neutralization

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Page 43


Topic 4 â&#x20AC;&#x201C; Acids and Bases (Part A)

Ch 14 Introduction of acid and alkalis / Ch 16 Indicator and pH / Ch 17 Strength / Ch 18 Salt and neutralization

www.hksciblog.edublogs.org/dse-chem

Page 44


Topic 4 â&#x20AC;&#x201C; Acids and Bases (Part A)

Ch 14 Introduction of acid and alkalis / Ch 16 Indicator and pH / Ch 17 Strength / Ch 18 Salt and neutralization

www.hksciblog.edublogs.org/dse-chem

Page 45


Topic 4 â&#x20AC;&#x201C; Acids and Bases (Part A)

Ch 14 Introduction of acid and alkalis / Ch 16 Indicator and pH / Ch 17 Strength / Ch 18 Salt and neutralization

www.hksciblog.edublogs.org/dse-chem

Page 46


Topic 4 â&#x20AC;&#x201C; Acids and Bases (Part A)

Ch 14 Introduction of acid and alkalis / Ch 16 Indicator and pH / Ch 17 Strength / Ch 18 Salt and neutralization

www.hksciblog.edublogs.org/dse-chem

Page 47

Topic 4 acid and base (parta)  
Topic 4 acid and base (parta)  
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