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Table 0 Common cations and anions: Positive ions (Cations) Charge Name Hydrogen ion Lithium ion Sodium ion +1 Potassium ion Silver ion Ammonium ion

+2

Formula F Cl Br I OH NO3

2+

Nitrite ion Hydrogencarbonate ion Hydrogensulphate ion Permanganate ion

NO2 HCO3 HSO4 MnO4

2+

Oxide ion Sulphide ion Sulphite ion Sulphate ion Chromate ion Dichromate ion

O 2S 2SO3 2SO4 2Cr2O4 2Cr2O7

Carbonate ion

CO3

Nitride ion Phosphate ion

3-

Magnesium ion Calcium ion Lead (II) ion Copper (II) ion

Mg 2+ Ca 2+ Pb 2+ Cu

Zinc ion Iron (II) ion Mercury (II) ion Manganese (II) ion Cobalt (II) ion Nickel (II) ion

Zn 2+ Fe 2+ Hg 2+ Mn 2+ Co 2+ Ni

Aluminum ion +3

Negative ions (Anions) Name Fluoride ion Chloride ion Bromide ion Iodide ion Hydroxide ion Nitrate ion

Formula + H + Li + Na + K + Ag + NH4

Iron (III) ion Chromium (III) ion

Charge

-1

-2

3+

Al

3+

Fe 3+ Cr

-3

--

2-

2-

N 3PO4

-ide = simple anion; -ite = polyatomic anion with less O atoms -ate = polyatomic anion with more O atoms Table 1 Colour of ions in aqueous solutions: Ion Color Ion Color Copper (II) Cobalt (II) Blue Pink 2+ 2+ Cu Co Nickel (II) Chromate Green Yellow 2+ 2Ni CrO4 Chromium (III) Dichromate Green Orange 3+ 2Cr Cr2O7 Iron (III) Permanganate Yellow Purple 3+ Fe MnO4 Pale pink Iron (II) Manganese (II) Green / 2+ 2+ Fe Mn colorless Table 3 Solubility of ionic compounds in water Compound of‌ Solubility in water + Potassium K All are soluble + Sodium Na All are soluble + Ammonium NH4 All are soluble Nitrate NO3 All are soluble Hydrogencarbonate All are soluble HCO3 All are soluble Halide X except AgX and PbX2 All are soluble 2Sulphate SO4 except CaSO4, PbSO4 and BaSO4 All are insoluble 2Carbonate CO3 except Na2CO3, K2CO3 and (NH4)2CO3 All are insoluble except K2O, Na2O, KOH 2Oxide O and and NaOH. hydroxide OH CaO and Ca(OH)2 are slightly soluble in water

Table 2 Flame colors of some common metal ions: Metal ion Sodium Potassium Calcium Copper (II)

Flame color Golden yellow flame Lilac flame Brick-red Bluish-green

Table 4 Solubility in water, colour and smell of gases Solubility Gas Color Smell in water Ammonia NH3 Soluble Colorless Pungent smell Sulphur dioxide Soluble Colorless Pungent smell SO2 Nitrogen dioxide Soluble Brown Pungent smell NO2 Pungent smell / Yellowish Chlorine Cl2 Soluble swimming pool green smell Hydrogen chloride Soluble Colorless Acidic smell HCl Hydrogen Soluble Colorless Bad egg smell sulphide H2S Slightly Oxygen O2 Colorless Odorless soluble Carbon dioxide Slightly Colorless Odorless CO2 soluble Hydrogen H2 Insoluble Colorless Odorless Nitrogen N2 Insoluble Colorless Odorless Carbon Insoluble Colorless Odorless monoxide CO


Table 5 Test for gases: Positive result Chemical equation (if any)

Gas

How to test

Hydrogen H2

Burning splint

Give a ‘pop’ sound 2H2(g) + O2(g)  2H2O(l)

Oxygen O2

Glowing splint

Glowing splint relights

Chlorine Cl2

Wet blue litmus paper

Carbon monoxide CO

Citrated blood

Carbon dioxide CO2

Lime water

Water vapor H2O

Anhydrous cobalt(II) chloride paper Anhydrous copper(II) sulphate powder

Blood turns from dark red to cherry red Limewater turns from colorless to milky Ca(OH)2(aq) + CO2(g)  CaCO3(s) + H2O(l)

Wet red litmus paper Ammonia NH3

Place near concentrated hydrochloric acid

Sulphur dioxide SO2

Blue litmus paper turns red and then white Cl2(g) + H2O(l) HCl(aq) + HOCl(aq) -( OCl (aq) + dye  (dye+O) + Cl aq)

Paper turns from blue to pink Powder turns from white to blue Red litmus paper turns blue NH3(g) + H2O(l) NH4+(aq) + OH-(aq) A dense white fume, NH4Cl(s) is formed NH3(g) + HCl(g)  NH4Cl

(bubble into) Acidified potassium dichromate solution

Dichromate solution turns from orange to green 2+ 3SO2(g) + Cr2O7 (aq) + 2H (aq) 23+  3SO4 (aq) + 2Cr (aq) + H2O(l)

(bubble into) Acidified potassium permanganate solution

Permangate solution turns from purple to colorless 5SO2(g) + 2MnO4 (aq) + 2H2O(l) 22+ +  5SO4 (aq) + 2Mn (aq) + 4H (aq)

(bubble into) Bromine water

Bromine water turns from orange to colorless SO2(g) + Br2(g) + 2H2O(l) 2+  SO4 (aq) + 2Br (aq) + 4H (aq)

Table 6 Test for cations: Cation

How to test

Observation Chemical equation and remarks

+

Potassium ion K + Sodium ion Na

No observable change + NaOH(aq): White precipitate is formed 2+ Ca (aq) + 2OH (aq)  Ca(OH)2(s)

2+

Calcium ion Ca

Magnesium ion Mg

Aluminum ion Al

Lead(II) ion Pb

Zinc ion Zn

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

2+

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

3+

2+

Add sodium hydroxide or ammonia solution

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

2+

Copper (II) ion Cu

2+

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

2+

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

3+

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

Iron (II) ion Fe

Iron (III) ion Fe

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) ‘少少醒就攞C’ Warm with A pungent gas which turns wet red litmus paper blue is produced + Ammonium ion NH4 sodium hydroxide NH4+(aq) + OH-(aq)  NH3(g) + H2O(l) solution


Table 7 Test for anions: Anions

Observation Chemical equation and remarks White precipitate is formed + Ag (aq) + Cl (aq)  AgCl(s)

How to test -

Chloride ion Cl

Bromide ion Br

Acidified silver nitrate solution

-

Pale yellow precipitate is formed + Ag (aq) + Br (aq)  AgBr(s) Yellow precipitate is formed + Ag (aq) + I (aq)  AgI(s)

-

Iodide ion I

2-

Carbonate ion CO3 2Hydrogencarbonate ion HCO3

Hypochlorite ion OCl

-

Dilute acid Add dilute acid and test the gas produced by a wet pH paper Acidified potassium dichromate solution Acidified potassium permanganate solution

2-

Sulphite ion SO3

Bromine water Add dilute acid and then test the gas produced by acidified potassium dichromate solution

Table 8 Metal reactivity series (M.R.S.) & Electrochemical series (E.C.S) E.C.S. M.R.S. Cations Anions + OH K K 2+ I Na Ca + Br Ca Na 2+ Cl Mg Mg 3+ NO3 Al Al 22+ SO4 Zn Zn 2+ Fe Fe 2+ Pb Pb + Cu H 2+ Hg Cu 2+ Ag Hg + Au Ag Table 9 Oxidation states of N and S Nitrogen Sulphur NO3 +5 H2S2O7 +6 2NO2 +4 SO4 +6 NO2 +3 SO3 +6 2NO +2 SO3 +4 N2 0 SO2 +4 NH3 -3 S8 0 H2S -2

Gas bubbles produced which turns limewater milky 2+ CO3 (s) + 2H (aq)  CO2(g) + H2O(l) + HCO3 (aq) + H (aq)  CO2(g) + H2O(l) A yellowish-green gas is produced which will turn wet pH paper to red and then white + OCl (aq) + Cl (aq) + 2H (aq)  Cl2(g) + H2O(l) Cl2(g) + H2O(l) HCl(aq) + HOCl(aq) -( OCl (aq) + dye  (dye+O) + Cl aq) Dichromate solution turns from orange to green 22+ 3SO3 (aq) + Cr2O7 (aq) + 8H (aq) 23+  3SO4 (aq) + 2Cr (aq) + 4H2O(l) Permangate solution turns from purple to colorless 2+ 5SO3 (aq) + 2MnO4 (aq) + 6H (aq) 22+  5SO4 (aq) + 2Mn (aq) + 3H2O(l) Bromine water turns from orange to colorless 2SO3 (aq) + Br2(aq) + H2O(l) 2+  SO4 (aq) + 2Br (aq) + 2H (aq) A pungent gas produced which turns dichromate solution from orange to green 2+ SO3 (aq) + 2H (aq)  SO2(g) + H2O(l)

Table 10 Reaction between metal and acids:

HCl(aq)

H2SO4(aq)

HNO3(aq)

Very dilute

Dilute

Concentrated

> Cu

> Cu

> Cu

 H2(g)

 H2(g)

 H2(g)

> Cu

> Cu

 Cu

 H2(g)

 H2(g)

 SO2(g)

> Cu

 Cu

 Cu

 H2(g)

 NO(g)

 NO2(g)


Table 11 Metal reactivity series / methods of metal extraction from its ores / reaction with oxygen, water and dilute acids MRS

Methods of extraction

Burns violently with a lilac flame 4K(s) + O2(g)  2K2O(s)

K

Burns violently with a golden yellow flame 4Na(s) + O2(g)  2Na2O(s)

Na

Ca

Electrolysis of its molten ores

White powder is formed 4Al(s) + 3O2(g)  2Al2O3(s)

Al

Powder (yellow when hot, white when cold) is formed. 2Zn(s) + O2(g)  2ZnO(s)

Zn

Heating with C (other possible reducing agent: H2(g), CO(g) and towngas)

Cu

Ag Au *

Iron powder burns with sparks Black solid is formed 3Fe(s) + 2O2(g)  Fe3O4 (a mixture of FeO and Fe2O3)

Reaction with water or steam Melts to a silvery ball Moves rapidly on the water surface Burns with a lilac flame Colourless solution is formed 2K(s) + 2H2O(l)  2KOH(aq) + H2(g)

Heating alone Exists as free element

Black powder is formed 2Cu(s) + O2(g)  2CuO(s) Red powder is formed 2Hg(l) + O2(g)  2HgO(s)

Reaction with dilute acids (HCl and H2SO4)

Explosive reaction. Never do it.

Similar to K, but burns with a golden yellow flame 2Na(s) + 2H2O(l)  2NaOH(aq) + H2(g)

Glows in steam White powder is formed Ca(s) + 2H2O(l)  Ca(OH)2(aq) + H2(g)

Glows in steam White powder is formed Mg(s) + H2O(g)  MgO(s) + H2(g)

React similarly as Mg with less vigor 2Al(s) + 3H2O(g)  Al2O3(s) + 3H2(g)

Reacts similarly as Al with less vigor Powder (yellow when hot, white when cold) is formed Zn(s) + H2O(g)  ZnO(s) + H2(g)

Reacts similarly as Zn with less vigor Black powder is formed 3Fe(s) + 4H2O(g)  Fe3O4(s) + 4H2(g)

Powder (orange when hot, yellow when cold) is formed 2Pb(s) + O2(g)  2PbO(s)

Pb

Hg

Burns with a brick-red flame 2Ca(s) + O2(g)  2CaO(s)

Burns with a bright white flame 2Mg(s) + O2(g)  2MgO(s)

Mg

Fe

Reaction with oxygen

Sink in acid Dissolves to give a colorless solution Gas bubbles are evolved Ca(s) + 2HCl(aq) CaCl2(aq) + H2(g) *Ca(s) + H2SO4(aq)  no apparent reaction Reacts similarly as calcium with less vigor Mg(s) + 2HCl(aq) MgCl2(aq) + H2(g) Mg(s) + H2SO4(aq)  MgSO4(aq) + H2(g) Reacts similarly as Mg with less vigor 2Al(s) + 6HCl(aq) 2AlCl3(aq) + 3H2(g) 2Al(s) + 3H2SO4(aq)  Al2(SO4)3(aq) + 3H2(g) React similarly as Al with less vigor Zn(s) + 2HCl(aq) ZnCl2(aq) + H2(g) Zn(s) + H2SO4(aq)  ZnSO4(aq) + H2(g) React similarly as Zn with less vigor A green solution is formed Fe(s) + 2HCl(aq) FeCl2(aq) + H2(g) Fe(s) + H2SO4(aq)  FeSO4(aq) + H2(g) *Pb(s) + HCl(aq) no apparent reaction *Pb(s) + H2SO4(aq)  no apparent reaction

No reaction No reaction

No reaction

Due to insoluble layer (CaSO4(s), PbCl2(s) and PbSO4(s)) is formed between metal and acid, which prevents further reaction.


Table 12 Test for carbon compounds: Functional group

How to test

Observation Chemical equation and remarks Bromine will be decolorized

Bromine in 1,1,1-trichloroethane Alkene C=C Permanganate turns from purple to colorless Acidified potassium permanganate solution Dichromate turns from orange to green o

Acidified potassium dichromate solution

1 alkanol:

Alkanol -OH o

2 alkanol: Fruity smell produced Warm with alkanoic acid and a few drops of conc. H2SO4 Orange precipitate (2,4-dintrophenylhydrazone) is formed. Carbonyl comound (aldehyde and ketone)

2,4dinitrophenylhydrazine

Aldehyde

Tollen’s reagent (Silver nitrate solution in excess ammonia solution)

Alkanoic acid –COOH

Silver mirror is formed on the surface of test tube + CH3CHO + 2[Ag(NH3)2] + 3OH  CH3COO + 2Ag + 4NH3 + 2H2O

Carbonate solution / hydrogencarbonate solution

Gas bubbles produced which turns limewater milky. + 2CH3COOH + Na2CO3  2CH3COO Na + H2O + CO2

Warm with alkanol and a few drops of conc. H2SO4

Fruity smell produced

Amine

Smell

Reducing sugar (all monosaccharide and most disaccharide except sucrose)

Tollen’s reagent Or Fehling’s reagent

Gaseous amines: smell of ammonia Liquid amines: fishy smell (Tollen’s reagent) Silver mirror is formed on the surface of (Fehling’s reagent) brick-red precipitate is formed

Table 13 Inter-conversion between different functional groups

DSE_Chem_key_table  

Anhydrous cobalt(II) chloride paper Paper turns from blue to pink Anhydrous copper(II) sulphate powder Powder turns from white to blue Green...

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