Handbook c3 acids, bases and salts

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Acids, Bases and Salts Handbook C3

"It’s very very dangerous to lose contact with living nature.�

-Albert Hofmann (1906-2008)

1

Handbook C3 Acids, Bases and Salts OVERVIEW OF HANDBOOK ABL ABL1

CONCEPT Introduction to acids and bases

NO OF ACTIVITIES

TIME min

PAGE NO

3

45

2

ABL2

Reaction of acids and bases with different substances

2

40

12

ABL 3

Neutralization reaction

3

55

21

ABL 4

Evaluation

3

25

30

ABL WITH REFERENCE TO STANDARD S. No 1 2 3 4

STANDARD 8, 9 9 9 8

RELEVANT ABL ABL 1 ABL 2 ABL 3 ABL 4

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LIST OF FIGURES, CHARTS AND WORKSHEETS S.No Chart 1.3 Chart 2.1 Chart 2.2 Worksheet 1 Worksheet 2 Worksheet 3 Worksheet 4

Name Acids and Bases Chart 1.3 Acids and Bases Chart 2.1 Acids and Bases Chart 2.2 Learner Observation sheet 1 Learner Observation sheet 2 Learner Observation sheet 3 Learner Observation sheet 4

Page Number 8 13 17 5 13 22 31

Note to Instructor: All the figures in this handbook are for the instructor’s reference only. The Charts need to be printed and shown to the students during the course of the activity. Worksheets need to be printed out in advance for the students. The number of worksheets required is mentioned in the Material List.

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ABL 1–Introduction to Acids and Bases Activity

Learning objective

Key messages

Time (min)

1.1

How do substances taste?



1.2

How do substances react with litmus paper?

 

1.3

Can we find acids and bases around us?

 

Substances can taste sour, bitter, sweet, salty or tasteless Sour substances which turn blue litmus paper red are called acids Bitter substances which turn red litmus paper blue are called bases Many common substances that we use everyday are acids and bases These substances have formal scientific names

15

15

15

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ABL 1.1

Time: 15 min

LEARNING OBJECTIVE – How do substances taste?

Note to Instructor – These activities show that substances can taste sour, bitter, sweet, salty or tasteless.

ADVANCE PREPARATION Material List Material 1 1 cup lemon juice 2 1 cup vinegar 3 ½ cup sugar 4 ½ cup common salt 5 1 cup baking soda solution 6 Spatula/wooden spoons 7 Observation sheet 1 8 Large Observation sheet 1

Number Required 1 per group 1 per group 1 per group 1 per group 1 per group 1 per learner 1 per learner 1 per class

Things to do Label all substances and place them on a table in the centre of the classroom.

Display the large version of Observation sheet 1 on the blackboard/whiteboard.Make sure that columns 3 and 4 (from the small Observation sheet 1) are not written on the large Observation sheet 1.

Safety Precautions Explain to the students that the substances that are used in this activity which they are being asked to taste, are not harmful. However, they should not taste substances that are used in the other activities.

SESSION Link to known information/ previous activity Not Applicable Procedure Divide the class into 5 groups. Assign each group one of the 5 substances. Give each learner an Observation sheet.Fold the Observation sheet between columns 2 and 3, so that only the columns 1 and 2 are visible. Ask them to move to their assigned work spaces. Ask each member of the groups to taste a small amount of the substances.Ask one learner from each of the groups to say what the substance tasted like. (I.e. sweet, sour, bitter, salty etc). Enter the response on the large Observation sheet. Instruct the learners to make entries into their own Observation sheets under column 2 – “Taste”. Repeat for all

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5 the groups, until the tastes of all 5 substances have been recorded on the observation sheets.

UNDERSTANDING THE ACTIVITY Leading questions 1. How do substances around us taste?

2. Is it safe to taste all of the substances around us?

3. If we cannot taste all substances, what are the other ways of identifying substances?

Discussion and Explanation 1. Substances can taste salty, sour, sweet, or bitter. Some have no taste at all.

2. It is not safe to taste all of the substances around us. Some substances may be poisonous or harmful.

3. We can identify substances by their colour, texture, change in appearance with time and their reactions with other substances.

KEY MESSAGES 

Substances can taste sour, bitter, salty or tasteless.

LEARNING CHECK Not Applicable

TRY IT YOURSELF Taste Test: Gather fruits and vegetables of different tastes, such as bitter gourd (karela), lemon (nimbu), papaya, tomato, onion, capsicum. Cut a small piece from each fruit or vegetable and mix them all together in a bowl. Sit down with the bowl in front of you and ask your friend to tie a blindfold around your eyes. Now pick up each piece of fruit or vegetable. Feel it, smell it and finally eat it. Try and guess the name of the fruit or vegetable. Ask your friend to tell you if you were right.

Time: 15 min

ABL 1.2 LEARNING OBJECTIVE - How do substances react with litmus paper?

Note to Instructor – Litmus paper reacts with different substances to show if they are acids and bases.

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ADVANCE PREPARATION Material List Materials 1 through 8 are same as in ABL 1.1.

Material 1 1 cup lemon juice 2 1 cup vinegar 3 ½ cup sugar 4 ½ cup common salt 5 1 cup baking soda solution 6 Spatula/wooden spoons 7 Observation sheet 1 Acids and Bases Observation Sheet 1.docx

8 9 10 11 12 13 14

Large Observation sheet 1 Plastic cups Stirrer Water cups Dropper 1 strips of red litmus paper 1 strips of blue litmus paper

Number Required 1 per group 1 per group 1 per group 1 per group 1 per group 1 per learner 1 per learner (this has already been given out in the previous exercise) 1 per class 1 per group 1 per group 1 per group 1 per group 1 per group 1 per group

Things to do Retain materials 1 through 8 from the previous ABL. Unfold Observation sheet 1 to show all the columns. Maintain same groups as previous ABL. Distribute additional material 9 through 14 to each group.Write headings of two additional columns on previously displayed large Observation sheet 1 “Does colour change to red?” and “Does colour change to blue?”

Safety Precautions Remind the learners that they should not taste the substances.

SESSION Link to known information/ previous activity Let’s try another method to identify the above substances without tasting or touching them. We will observe how they react with another substance called litmus. Litmus is a dye that has been extracted from lichens which are tiny plants. The dye is coated on a piece of paper. This coated paper is called litmus paper. Today, we will be using red litmus paper and blue litmus paper to identify substances.

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7 Procedure Ask all the learners to unfold their observation sheets. Ask one member of each group to mix some water with the substancegiven to themin a plastic cup/ tumbler/ test tube. Ask them to put a drop of the solution on both, the red litmus paperand the blue litmus paper with the help of a dropper. Ask each learner to note down what happens to the litmus paper in theirObservation sheets.

Ask a learner from each group to state the effect of their substance on the litmus paper and to display the litmus paper to the rest of the class. Ensure that this learner is different from the learner in the previous activity. All learners note down the reaction of the litmus paper in their Observation sheets. The instructor notes down the reaction on the large Observation sheet.

UNDERSTANDING THE ACTIVITY Leading questions 1. Which substances turn the red litmus paper blue?

2. Which substances turn the blue litmus paper red?

3. Which substances had no effect on both the red litmus paper and the blue litmus paper?

4. Is there any relationship between the taste of the substance and its effect on the litmus paper?

5. Is there a name for substances that react with the litmus papers and change their colour?

6. Can you guess why litmus is called an indicator?

Discussion and Explanation 1. Lemon juice and vinegar turn the blue litmus paper red, the red litmus paper stays the same 2. Baking soda solution turns the red litmus paper blue, the blue litmus paper stays the same 3. Sugar and common salt do not change the colour of the blue litmus paper or the red litmus paper 4. Substances that are sour to taste turn blue litmus paper red. Substances that taste bitter and are soapy to touch turn red litmus paper blue.

5. Substances that are sour turn blue litmus paper red. We call these types of substances “acids”. Substances that are bitter turn red litmus paper blue.

We call these types of substances “bases”. Some bases that dissolve in water are called “alkalis”.Substances that do not have any effect on either red or blue litmus paper are called “neutral” substances.

6. Litmus “indicates” whether a substance is an acid or a base. This why it is called an indicator.

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KEY MESSAGES Sour substances which turn blue litmus paper red are called acids Bitter substances which turn red litmus paper blue are called bases

 

LEARNING CHECK True or False?

1.

2.

3.

4.

5.

6.

Bases change red litmus paper to blue Acids turn blue litmus paper to green A property of an acid is its sour taste Tamarind is sour and turns red litmus paper blue Tomato juice is sour and therefore acidic All bases are also known as alkalis

Answers: 1.

2.

3.

4.

5.

6.

(T) (F) Acids turn blue litmus paper red (T) (F) Tamarind is sour and therefore acidic, it turns blue litmus paper red (T) (F) Only bases that dissolve in water are known as alkalis

Time: 15 min

ABL 1.3 LEARNING OBJECTIVE –Can we find acids and bases around us?

Note to Instructor – Acids and bases are commonly found around us in the foods we eat and substances we use.

1 2 3 4 5 6 7 8 9 10 11

Material 1 cup lemon juice 1 cup vinegar ½ cup sugar ½ cup common salt 1 cup baking soda solution Spatula/wooden spoons Observation sheet 1 Large Observation sheet 1 Plastic cups Stirrer Water cups

Number Required 1 per group 1 per group 1 per group 1 per group 1 per group 1 per learner 1 per learner 1 per class 1 per group 1 per group 1 per group

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9 12 13 14 15 16 17 18

Dropper 1 strips of red litmus paper 1 strips of blue litmus paper Pink/ red cardboard square Blue/green cardboard square Marker/sketch pen Display version of Chart 1.3

1 per group 1 per group 1 per group 1 per learner 1 per learner 1 per learner 1 per class

Acids and Bases Table 1.3.docx

Things to do Retain all the materials and groups from the previous ABL. Instructions for material 15 through 17: In each of the pink/red cardboard square, write the common name of one acid such as: vinegar, ant’s sting, lemon, orange, curd, spinach (palak), tamarind, and mango.

In each of the blue/green cards write the common name of a base such as: lime water, window cleaner, soap, milk of magnesia.

It is ok for two cards to have the same name, but there should only be one name per card.

Distribute one blue/green and one pink/red card per learner.

Safety Precautions Remind the learners that they should not taste the substances.

SESSION Link to known information/ previous activity We now know that substances can be identified as acids and bases by testing with litmus paper. Some of those substances were familiar to us. Let us learn more about acids and bases around us.

Procedure- 1 Ask learners with red/pink cards to form one group. Ask learners with blue/green cards to form another group. Ask each learner to read the name of the substances written on the cards.

Leading questions-1 1. What could the type of substances on the pink cards be?

2. What could the type of substances on the blue cards be?

3. Have you seen some of these substances used in your daily life?

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Discussion and Explanation-1 1. We have seen some of the substances on the pink cards turn blue litmus paper red. They must be acids.

2. We have seen some of the substances on the blue cards turn red litmus paper blue. They must be bases.

3. Acids and bases are found all around us. We know them by different names and use them for different purposes.

Link to known information/ previous activity2 Once a substance is identified as an acid or a base, scientists give these substances a formal scientific name. Let’s look at the formal scientific names of the substances on your cards.

Procedure- 2 Display Chart 1.3 to the whole class. Call upon learners to read out the name of the substance on their card. For each substance, show and read out the corresponding, formal scientific name from Chart 1.3. Ask all learners with a card of this substance name to write down the formal name on the back of their card. Repeat until all the names on the chart have been read. The learners can carry these cards home as take-home cards.

Leading questions-2 1. What could the type of substances on the pink cards be?

2. What could the type of substances on the blue cards be?

3. Have you seen some of these substances used in your daily life?

Discussion and Explanation-2 1. We have seen some of the substances on the pink cards turn blue litmus paper red. They must be acids.

2. We have seen some of the substances on the blue cards turn red litmus paper blue. They must be bases.

3. Acids and bases

KEY MESSAGES  

Many common substances that we use everyday are acids and bases These substances have formal scientific names

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LEARNING CHECK Ask learners to list the key things they have learnt. Guide them to the key messages listed and then put up the chart of key messages. If you have time during the class, make up a small game, quiz or match the following as a learning check. This may have to be done as part of advance preparation

TRY IT YOURSELF Make your own acid-base indicator: Many substances around us are acids and bases and can be tested with litmus paper. However, litmus paper may not be available easily. Acid-base indicators can also be made using easily available material.

1) Turmeric Indicator – Take half a teaspoon of turmeric powder and mix it with 10mL of water. Measure the water using the plastic measuring cup of a used medicine bottle. Pour this turmeric mixture equally into two transparent cups. Using separate droppers, place a few drops of lemon juice into one cup and a few drops of soap solution into the other. What happens to the liquids in the cups?

(Turmeric turns pink when it comes into contact with a base such as soap solution. It stays the same colour when it comes into contact with an acid such as lemon juice.)

2) Beetroot Indicator– Cut a beetroot into small pieces and grind to a paste in a blender. Remove the paste into a bowl. Add half a cup of boiling water to this paste. Mix well and using a strainer, pour the liquid into a container. Take 3 teaspoons of vinegar in a transparent cup and 3 teaspoons of soap solution in another transparent cup. Using a dropper, drop a few drops of the beetroot extract into both the liquids. What happens to the liquids in the cups?

(Beetroot liquid turns red when it comes into contact with an acid such as vinegar (acetic acid). It turns to the colour yellow in the second cup when it comes into contact with the base in the soap solution (sodium hydroxide).

INTERESTING INFORMATION 1) What is an indicator?

Litmus is called an indicator becauseit indicates whether the substancebeing tested is acidic or basic.

2) What is litmus paper?

Litmus is a water-soluble mixture of different dyes extracted from plants called Lichens. It is coated onto filter paper which is used to indicate if substances are acids or bases. Substances which do not change the color of either red or blue litmus are Agastya International Foundation. For Internal Circulation only.

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12 known as neutral solutions. These substances are neither acidic not basic. Purple litmus paper can be used to check for both acids and bases.

3) Why does litmus paper change its color?

The litmus paper is an acid-base indicator, and the change in color is attributed to the formation of a compound that is dependent on the number of H+ ions.

4) What is Aquaregia?

It is a very powerful acid that can dissolve gold. It is made up of one part of concentrated nitric acid and three parts of concentrated hydrochloric acid.

5) What is the name of the acid used in car batteries?

Sulphuric acid is used in car batteries. It is a strong mineral acid that is highly corrosive.

6) What happens when you don’t brush your teeth after eating sweets?

Bacteria in our mouths convert the sugar into acids such as lactic acid which attack the teeth and cause decay.

7) What is the name of the bacteria that convert milk to curds?

Lactobacillus converts the sugar in milk into lactic acid which turns the milk into curds.

WEB RESOURCES  

http://www.bbc.co.uk/bitesize/ks3/science/chemical_material_behaviou r/acids_bases_metals/revision/4/ http://pbskids.org/zoom/games/kitchenchemistry/virtual-start.html

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ABL 2– How do acids and bases react with different substances?

Activity

Learning objective

Key messages

Time (min)

2.1

How do acids react with metals?

 

2.2

How do acids react with metal carbonates?



Acids react with many metals and release hydrogen gas Metals react differently with acids; copper, silver and gold do not react with weak acids Acids react with metal carbonates to release carbon dioxide gas

20

15

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ABL 2.1

Time: 20 min

LEARNING OBJECTIVE – How do acids react with metals?

Note to Instructor – Acidsreact with many metals to release hydrogen gas.

ADVANCE PREPARATION Material List 1.

Material 15 ml of 50% dilute hydrochloric acid

Number Required 1 per class

2.

2.5 inches magnesium ribbon

1 per class

3.

2 to 5 pieces zinc metal flakes

1 per class

4.

2 to 5 pieces copper flakes

1 per class

5.

2 boiling test tubes

1 per class

6.

Test tube stand

1 per class

7.

Wooden splint

1 per class

8.

Matchbox

1 per class

9.

Dropper

1 per class

10. Observation sheet 2

1 per learner

Acids and Bases Observation Sheet 2.docx

11. Large Observation sheet 2

1 per class

12. Chart 2.1

1 per class

Acids and Bases Table 2.1.docx

13. 2 pairs gloves

1 per class

14. 2 pairs safety goggles

1 per class

Things to do Prepare stock solutions of dilute acids beforehand. Use the dilute acids in smaller amounts as needed. Prepare dilute acid solution by adding required amount of concentrated acid to a beaker of water.

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15 Prepare Observation sheet 2 and Chart 2.1beforehand. Place large Observation sheet 2 at the front of the class, taped to the blackboard/whiteboard or to the wall.

Set up one test tube in the test tube stand at the front of the class. Place the other test tube, matchbox, metal pieces to be tested, the container with the dilute hydrochloric acid and the dropper on a table next to the test tube stand. Provide gloves and goggles to each learner performing the experiment.

Safety Precautions Be careful while handling chemicals. Make sure that you use gloves and goggles.

This activity is to be performed strictly under instructor supervision. Do not let the learners handle the materials unsupervised.

Never pour water into a container of concentrated acid.

SESSION Link to known information/ previous activity We have learnt how acids and bases react with litmus paper. Let’s see how they react with substances such as metals.

Procedure Divide the class into 3 groups. Assign one of the following metal-acid pairs to each group. DO NOT distribute the materials to the groups. Distribute Observation sheet 2 to each learner. Ask 2 learners (learner 1 and learner 2) from each group to come up to the front of the class to conduct the experiment. Check to see which metal-acid pair has been assigned to their group and provide material accordingly.

2.1a Reaction of metal with acid Ask the two learners to put on the goggles and gloves before starting the experiment. Ask learner 1 to add a few granules of the metal, to the test tube clamped to the vertical stand. Ask the two learners to observer the surface of the metal granule. Call some of the learners to state their observations. Ask all the learners to note down their observations in Observation sheet 2. Write the observation on the large Observation sheet 2. Now ask the Learner 1 to add few drops of dilute acid to the metal pieces.

2.1b Testing the gas generated Ask learner 2 to bring a lighted wooden splint (match stick) to the mouth of the test tube as shown in Figure 2. Call upon a different set of learners to state their observations. Ask all the learners to note down their observations in Observation sheet 2. Repeat this activity with the next metal-acid pair for learners from the next group until all 3 groups complete their experiments.

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Figure 2

UNDERSTANDING THE ACTIVITY 2.1a Reaction of metal with acid Leading questions 1. What do you observe at the surface of the metal pieces after the acid is added?

2. What could be an explanation for this reaction that releases hydrogen gas?

3. What are the other products of this metal-acid reaction?

Discussion and Explanation 1. Bubbles are seen at the surface of the metal for Zinc and Magnesium.

Bubbles are not generated for Cu. This is because some metals react with acid to release hydrogen gas. Zinc and Magnesium react with hydrochloric acid to release hydrogen gas. Copper does not react with the hydrochloric acid, which is why no bubbles are seen.

2. This reaction takes places because the metal moves or displaces from the acids. The displaced hydrogen is released as hydrogen gas. The reaction is shown in Chart 2.1. (Display Chart 2.1).

3. We have seen that metal and acid react to produce hydrogen. This reaction also produces a metal “salt�. Common salt, known as sodium chloride, is produced when sodium metal reacts with an acid.

2.1b Testing the gas generated

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17 Leading questions 1. What happens when the lighted wooden splint is brought near the mouth of the inverted test tube?

2. What could be an explanation for the effect on the lighted splint?

3. Why is the “pop” sound taken as an indicator for the presence of hydrogen?

4. Why is there no “pop” sound for the Copper and hydrochloric acid reaction?

Discussion and Explanation 1. A “pop” sound is heard 2. The “pop” sound is heard because the flame ignites the hydrogen in the test tube, which burns explosively to make a loud sound.

3. In the same way that the change in colour of litmus paper indicates the presence of an acid or a base, the “pop” sound indicates the presence of hydrogen. This is because only hydrogen gas explodes with the explosive “pop” sound.

4. Metalssuch as zinc and magnesium are more reactive than hydrogen. They removeor displace hydrogen fromhydrochloric acid and form a compound with chlorine resulting in a salt.Because copper is a metal that is less reactive than hydrogen, it is not able to displace hydrogen from hydrochloric acid.

Because of this, no reaction occurs and no hydrogen gas is released. This is also true of gold and silver.

KEY MESSAGES  

Many metals react with acids and release hydrogen gas.

Metals differ in their reactivity towards acids. Metals like copper, silver and gold do not react with dilute acids.

LEARNING CHECK The following multiple choice questions can be used in a worksheet or as a quiz to see how much has been understood by the class. Answers are given after the questions 1. Curd and other sour substances should not be stored in brass vessels (made from copper and lead) for health reasons because: a. Curd turns sour in brass vessels b. Brass promotes the growth of harmful bacteria c. Curd is an acid and reacts with the copper to produce poisonous copper salts d. There is no reason why curd should not be stored in brass vessels Agastya International Foundation. For Internal Circulation only.

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18 2. Copper reacts with hydrochloric acid to produce: a. Copper chloride b. Copper nitrate c. Copper hydrate d. It does not react with hydrochloric acid 3. Magnesium reacts with hydrochloric acid to produce: a. Oxygen b. Hydrogen c. Carbon dioxide d. It does not react with hydrochloric acid 4. The presence of hydrogen gas is indicated by: a. A lighted splint b. Red litmus paper c. Blue litmus paper d. Smell of rotten eggs

(Answer for Instructor’s Reference: 1.c, 2.d, 3.b, 4.a) Time: 20 min

ABL 2.2 LEARNING OBJECTIVE – How do acids react with metal carbonates?

ADVANCE PREPARATION Material List Material 1. 10 ml of 50% dilute hydrochloric acid 2.

Number Required 1 per group 1 per group

3.

15 ml calcium hydroxide solution (lime water) 5 gm sodium carbonate powder

4.

2 test tubes

1 per group

5.

Test tube holder

1 per group

6.

Test tube stand

1 per group

7.

1 per group

8.

Delivery tube with rubber stoppers on either side (to fit the test tubes) Dropper

9.

Spatula

1 per group

1 per group

1 per group

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19 10. 2 pairs gloves

1 per group

11. 2 pairs safety goggles

1 per group

12. Chart 2.2

1 per class

Acids and Bases Table 2.2.docx

Things to do Attach a test tube containing the sodium carbonate powder to the test tube stand as shown in Figure 3. Prepare the dilute hydrochloric acid solution if not already prepared.

Safety Precautions Instruct learners to use gloves at all times and to be careful while performing the experiment.

SESSION Link to known information/ previous activity We have seen that acids react with metals to produce a metal salt and release hydrogen. Now let us see how acids react with other substances such as metal carbonates.

Procedure Divide the learners into 4 groups. Distribute the material to each group. Set up the apparatus for each group as shown in figure 3.Do not attach the rubber stoppers/delivery tube to the test tubes. Leave the other test tube open. Instruct the users to place 5 gms of sodium carbonate in the empty test tube. Ask them to carefully add 2 ml of dilute hydrochloric acid to sodium carbonate powder using the dropper. Attach the rubber stopper to both the test tube making sure that one end of the delivery tube sips into the limewater. As the substances react, observe the changes over a period of time.

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Figure 3

UNDERSTANDING THE ACTIVITY Leading questions 1.

2.

3.

4.

What happens when the hydrochloric acid is added to the sodium carbonate?

What happens to the lime water?

What could be the cause for the colour change?

Does the colour remain milky?

Discussion and Explanation 1. Bubbles form when the sodium carbonate and hydrochloric acid mix. A gas is released in the form of bubbles. This gas is carbon dioxide gas.

2. The lime water which was clear became milky 3. The carbon dioxide gas from the sodium carbonate and hydrochloric acid reaction bubbles into the limewater and may be reacting with it. Carbon dioxide has the property to turn limewater milky. Carbon dioxide reacts with lime water to produce calcium carbonate that is white in colour. This turns lime water milky. (Display Chart 2.2) 4. As the bubbling continues, the colour of the lime water becomes clear again.

This is because calcium carbonate further reacts with lime water to produce calcium bicarbonate that dissolves in lime water

KEY MESSAGES 

Acids react with metal carbonates and release carbon dioxide gas

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21

LEARNING CHECK Ask learners to list the key things they have learnt. Guide them to the key messages listed and then put up the chart of key messages. If you have time during the class, make up a small game, quiz or match the following as a learning check. This may have to be done as part of advance preparation

TRY IT YOURSELF Mix one teaspoon of plain chuna (which is eaten with betel leaves) with an empty glass bottle of water. This is limewater. Now, use a straw to blow into the limewater. Keep blowing until the limewater turns milky. (Do not drink the limewater.)  Why does the limewater turn milky?  What is in the air that we breathe out?

INTERESTING INFORMATION The reactivity series of metals is a list of metals arranged in order of decreasing reactivity. The most active metals appear at the top of this list and the least active metals are at the bottom. This series is helpful in predicting metal displacement reactions and the reactions of metals with different acids, reactions with cold water and reactions with oxygen.The series works well as long as the reactions being predicted occur at room temperature and in aqueous solution.

In displacement reactions the reactivity series can predict the outcome of the following two reactions: In Reaction 1, zinc is more reactive than hydrogen, and so it will replace it and form a salt with chlorine. In Reaction 2, because copper is less reactive than hydrogen, it will not displace hydrogen from acids. Reaction 2 will not progress.

Zn + 2HCl --> ZnCl2 + H2 ------- Reaction 1 Cu + HCl -->????

------- Reaction 2 Reactivity series of some common metals is as shown in the figure. Hydrogen and carbon are added in the series for comparison of reactivities:

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1

WEB RESOURCES http://www.bbc.co.uk/bitesize/ks3/science/chemical_material_behaviour/comp ounds_mixtures/revision/5/ http://chemistry.about.com/od/chartstables/a/Activity-Series-Of-Metals.htm

1http://www.docbrown.info/page12/gifs/ReactivitySeriesList.gif

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23

ABL 3– Neutralization Reaction Activity

Learning objective

Key messages

Time (min)

3.1

How do acids and bases react with each other?

 

3.2

3.3

How does a nonmetallic oxide react with a base?



How does a metallic oxide react with an acid?







When acids and bases react, salt 30 and water are formed The reaction is called neutralization Many non-metallic oxides are 10 acidic in nature Many non-metallic oxides react with bases to form salt and water Metallic oxides are basic in nature Metallic oxides react with acids to form salt and water

15

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24

ABL 3.1

Time: 30 min

LEARNING OBJECTIVE – How do acids and bases react with each other?

Note to Instructor – Acids and bases react with each other to produce salt and water in a neutralization reaction.

ADVANCE PREPARATION Material List Material 10 ml of 1% sodium hydroxide (NaOH)

Number Required 1 per group

10 ml of 1% dilute hydrochloric acid (HCl) 1 bottle of phenolphthalein

1 per group

1 per group

5.

5 strips of purple litmus paper (to check for both acid and base) Beaker/conical flask

6.

2 droppers

1 per group

7.

2 stirrers

1 per group

8.

Observation sheet3

1 per learner

1.

2.

3.

4.

1 per group

1 per group

Acids and Bases Observation Sheet 3.docx

9.

Large Observation sheet3

1 per class

10. 2 pairs gloves

1 per class

11. 2 pairs safety goggles

1 per class

Things to do Prepare solutions of 1% dilute hydrochloric acid and 1% dilutesodium hydroxide. Make sure they are of equal dilution. Divide learners into groups of 4 to 6 per group. Distribute materials and apparatus to each group. Distribute observations sheet 3 to each learner. Provide gloves and goggles to each learner performing the experiment.

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25 Safety Precautions Instruct learners to be careful while handling chemicals. Make sure they use gloves and goggles.

SESSION Link to known information/ previous activity So far we have seen how acids react with metals and liberate hydrogen. We have looked at how metal carbonates react with acids and release carbon dioxide. We have also learnt how carbon dioxide reacts with limewater and makes it milky.

Now we will see what happens when acids and bases react with each other.

Procedure Since this activity has several steps, different learners from a group can take turns with adding the acid, base, indicator or conducting the litmus base. Identify the learners who will be conducting the different steps.

Explain to the learners that this activity involves different steps where the dilute base and dilute acid are added to each other step by step.

Ask the learners to take 2 ml of dilute sodium hydroxide solution in a test tubs and add 2 drop of phenolphthalein solution. Drop a few drops of the solution on the litmus paper to check if the solution is acidic, basic or neutral. Ask them to fill in rows 1,2 and 3 of the Observation sheet 3. Next, ask them to add dilute hydrochloric acid solution to the above solution drop by drop and constantly shake the sodium hydroxide solution so that it mixes with the hydrochloric acid.

Ask them to keep track of the exact drop of hydrochloric acid addedthat changes the colour of the solution.Ask the learners to conduct the litmus paper test on a fresh strip of litmus. Ask them to fill in rows 4 and 5 of Observation sheet 3. Ask them to add 5 to 10 more drops of hydrochloric acid. Again, ask them to conduct the litmus test on another fresh litmus strip and fill in rows 6, 7 and 8 of the Observation sheet 3. Ask them to add sodium hydroxide to the mixture drop by drop until the colour reappears. Ask them to keep track of the exact drop of sodium hydroxide added that changes the colour of the solution. Ask the learners to conduct the litmus paper test on a fresh strip of litmus. Fill in rows 9 and 10 and inferences 1 and 2, of Observation sheet 3.

UNDERSTANDING THE ACTIVITY Leading questions 1. What is the colour of sodium hydroxide solution when phenolphthalein is added?

2. When does the colour of solution change?

3. Is the solution acidic or basic when the solution becomes colourless?

4. What happens when more hydrochloric acid is added?

5. What happens when sodium hydroxide is added again?

6. How is the acidity/basicity of the medium changing as the experiment proceeds?

7. How does phenolphthalein help to indicate what is happening to the solution?

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26 8. Where do we use neutralization reactions in daily life?

9. In case of an acid spill on skin, should we neutralize the site of exposure with a base?

Discussion and Explanation 1. Sodium hydroxide solution becomes pink when phenolphthalein is added 2. As you add acid drop by drop, the solution remains pink. The colour becomes lighter and lighter until at one point it completely vanishes and the solution becomes colourless. At this point the solution is neither basic nor acidic as indicated by no change in colour of the litmus paper.

3. When the solution turns colourless, the litmus test indicates that the solution is neutral – that is, it is neither acidic nor basic.

4. Even with excess acid, phenolphthalein remains colourless. But the litmus test shows red colour. So the solution must have become acidic.

5. When sodium hydroxide is added again, it stays colourless in the beginning.

But at some point the colour starts appearing again. When more sodium hydroxide is added the solution becomes fully pink. Litmus paper turns blue again, indicating that the solution is basic.

6. Like litmus, phenolphthalein is also an indicator of acidity/basicity of the solution. When litmus test showed blue – phenolphthalein was pink. When litmus test shows no change or red – phenolphthalein is colourless. So phenolphthalein is pink in basic medium, but colourless in neutral and acidic medium.

7. It is clear that phenolphthalein is pink in basic medium. Something makes the basicity reduce and disappear when acid is added. The effect of the acid is being nullified by the effect of the base.This nullification process is called “neutralization” and the point where the pink solution becomes colourless is called the neutral point. (Display Table 3.1) 8. Neutralization reactions are used in daily life. In the case of insect stings the acid released by the sting can be neutralized by a basic solution of sodium bicarbonate (baking soda). Antacids are medicines containing bases to neutralize excess stomach acid for patients with gastric problems.

9. No. The best treatment is to immediately wash off the acid with plenty of water. Pouring a base on the acid spill area of the skin causes neutralization which releases heat and can further damage the skin. Strong bases can be as corrosive as acids and pouring this on skin is also dangerous.

KEY MESSAGES  

When acids and bases react, salt and water are formed This reaction is called neutralization

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27

LEARNING CHECK Not Applicable Time: 10 min

ABL 3.2 LEARNING OBJECTIVE – How does a non-metallic oxide react with a base?

Note to Instructor – Non-metallic oxides tend to be acidic in nature and react with bases to give salt and water.

ADVANCE PREPARATION Material List 1.

Material Milky lime water in a test tube

Number Required 1 per class

Things to do Not Applicable Safety Precautions Not Applicable

SESSION Link to known information/ previous activity We have seen that acid and base react to give salt and water. Now, let us see how a base reacts with some other substances called non-metallic oxides. Nonmetallic oxides are formed when a substance that is not a metal reacts with oxygen.

Procedure Explain to the students that when we leave a cut banana or a cut potato for some time, we see that it turns brown. This is because the substances that are present in the banana react with the oxygen in the air to produce “oxide” compounds.

Tell the students that non-metallic oxides are formed when some substances react with oxygen. Explain that this process is known as “Oxidation”.

Display the milky lime water. On the blackboard write:

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Neutralization reaction:

28

Base + Acid = Salt + Water Milky water reaction: Calcium hydroxide + Carbon dioxide ---------->Calcium carbonate + Water

Ca(OH)2+ CO2----------> CaCO3 + H2O On the blackboard draw an arrow from “Base” to “Calcium hydroxide”,from“Salt”to“Calcium carbonate”. Write the chemical formula for each compound under each name.

UNDERSTANDING THE ACTIVITY Leading questions 1. What is the neutralization reaction?

2. What is the reaction between carbon dioxide and the base?

3. Identify the base and the salt in this reaction?

4. What is similar between the neutralization reaction and the milky water reaction?

5. Identify the acid in this reaction?

Discussion and Explanation 1. Neutralization reaction is: Base + Acid Salt + water 2. Milky water reaction is calcium hydroxide plus carbon dioxide gives calcium carbonate plus water 3. Calcium hydroxide is the base in the milky water reaction. Calcium carbonate is a salt 4. Milky water reaction can also be written as : Base + Non Metallic Oxide  salt + water Out of the 4 components, 3 components are common to both the reactions.

They are: base, salt and water.

The only thing left is the acid (neutralization reaction) and carbon dioxide (milky water reaction).

5. Since carbon dioxide and base are forming salt and water, we can conclude that carbon dioxide is the acid component in the reaction.

Oxides of non-metals like sulphur, nitrogen and phosphorus are also acidic. However not all oxides of non-metals are acidic. Water, the oxide of hydrogen is neutral!

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KEY MESSAGES  

Many Non metallic oxides react with bases to form salt and water Many Non metallic oxides are acidic in nature

LEARNING CHECK Ask learners to list the key things they have learnt. Guide them to the key messages listed and then put up the chart of key messages. If you have time during the class, make up a small game, quiz or match the following as a learning check. This may have to be done as part of advance preparation

INTERESTING INFORMATION Oxides produced When coal, petrol or diesel are burnt, they produce oxides. These oxides form acids when they react with the moisture in the atmosphere. This results in acid rain which harms trees, crops, houses and most things on the ground. This is one reason why we say that pollution from vehicles is harmful for the environment.

Time: 15 min

ABL 3.3 LEARNING OBJECTIVE – How does a metallic oxide react with an acid?

Note to Instructor – Metallic oxides tend to be basic in nature and react with acids to give salt and water.

ADVANCE PREPARATION Material List 1.

Material 5 gm copper oxide

Number Required 1 per group

2.

10 ml dilute hydrochloric acid

1 per group

3.

Beaker

1 per group

4.

Dropper

1 per group

5.

Stirrer

1 per group

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30 Things to do Prepare solutions of 1% dilute hydrochloric acid. Measure out the copper oxide and place it in beakers. Distribute the materials and apparatus to each group.

Safety Precautions Instruct learners to be careful while handling chemicals. Make sure they use gloves and goggles.

SESSION Link to known information/ previous activity We have seen that non-metallic oxides act as acids in the milky water reaction.

Now let us see how metallic oxides behave.

Procedure Explain to the students that metallic substances such as copper, iron, sodium etc also oxidize to form metallic oxides. Tell that that they will be learning about the metallic oxide, copper oxide.

Divide learners into groups of 4 to 6. Ask one learner from each group to slowly add the measured amount of hydrochloric acid to the copper oxide in the beaker.

Ask another learner to stir the solution using the stirrer. Ask all the learners to observer the colour of the solution.

UNDERSTANDING THE ACTIVITY Leading questions 1. What is the colour of the copper oxide?

2. What is the colour of the hydrochloric acid?

3. What is happening to the copper oxide as hydrochloric acid is added?

4. What is happening to the colour of the solution?

5. Why do you think this is happening?

6. Which reaction could be taking place?

7. What is similar between the neutralization reaction and this reaction?

8. Identify the base in this reaction?

Discussion and Explanation 1. Copper oxide is a white powder 2. Hydrochloric acid is colourless 3. Copper oxide seems to be dissolving 4. Colour of the solution is changing from colourless to blue 5. The hydrochloric acid is reacting with copper oxide to form a blue-green salt Agastya International Foundation. For Internal Circulation only.

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31 6. The metal oxide could be reacting with the acid to form salt plus water a. Write on the board: Neutralization reaction: Base + Acid = Salt + Water Metal oxide reaction: Copper oxide + Hydrochloric acid ---------->Copper chloride + Water

CuO + 2 HCl ----------> CuCl2 + H2O

7. Out of the 4 components, 3 components are common to both the reactions.

They are: acid, salt and water.

8. The only component left is the base (neutralization reaction) and copper oxide in the metal oxide reaction Since copper oxide and acid are forming salt and water, we can conclude that copper oxide is the base component in the reaction.

KEY MESSAGES  

Many metallic oxides react with acids to form salt and water Many metallic oxides are basic in nature

LEARNING CHECK Ask learners to list the key things they have learnt. Guide them to the key messages listed and then put up the chart of key messages.If you have time during the class, make up a small game, quiz or match the following as a learning check. This may have to be done as part of advance preparation

INTERESTING INFORMATION Oxides produced when coal, petrol or diesel are burnt, form acids when they react with the moisture in the atmosphere. This results in acid rain which harms trees and buildings

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32

ABL 4– Conclusion Activity

Learning objective

Key messages

Time (min)

4.1

Is the solution acidic or basic?



4.2

Can you match the indicator with the substance it indicates?

How do acids and bases behave?



4.3

 

Solutions can be tested for acidity or basicity using different indicators There are specific indicators for different substances

10

Acids and bases exhibit typical behaviour with certain substances A substance can be tested for acidity/basicity based on these behaviours

10

5

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ABL 4.1

Time: 10 min

LEARNING OBJECTIVE – Is the solution acidic or basic?

Note to Instructor – Solutions can be tested to see if it is an acid or a base by using red and blue litmus paper.

ADVANCE PREPARATION Material List 1.

Material 4 test tubes

Number Required 1 per group

2.

4 strips of blue litmus paper

1 per group

3.

4 strips or red litmus paper

1 per group

4.

Phenolphthalein Indicator

5.

Dropper

1 per group

6.

Observation sheet 4

1 per learner

Acids and Bases Observation Sheet 4.docx

Things to do Prepare 4 test tubes with either dilute acidic solutions or dilute basic solutions.

These can be 2 acidic and 2 basic solutions or 3 acidic and 1 basic solution. (Or vice versa). Label these solutions “A”, “B”, “C” and “D”.Write down which each of the solutions is and keep it with you.

Safety Precautions Instruct learners to be careful while handling chemicals and tell them not to taste the chemicals. Make sure they use gloves.

SESSION Link to known information/ previous activity We have learnt about how we can test for acids and bases in different ways. Now let us test some solutions to see if they are acids or bases.

Procedure Explain to the learners that the 4 solutions contain acidic or basic solutions. The learners have to test to see if each solution is acidic or basic withouttasting the solution or adding water to the solution.

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34 Divide learners into groups of 4. Give them 2 minutes to brainstorm and come up with different ways they can test the solutions. Give them the litmus paper or phenolphthalein indicator as requested. Instruct them to enter their observations in the table in Observation sheet 4.

UNDERSTANDING THE ACTIVITY Leading questions 1. Which of the solutions was acidic and which was basic?

2. Which were the tests you used?

Discussion and Explanation 1. Confirm findings using the answer key 2. Read from Observation sheet 4

KEY MESSAGES 

Solutions can be tested for acidity or basicity using different indicators

LEARNING CHECK Ask learners to list the key things they have learnt. Guide them to the key messages listed and then put up the chart of key messages. If you have time during the class, make up a small game, quiz or match the following as a learning check. This may have to be done as part of advance preparation Time: 5 min

ABL 4.2 LEARNING OBJECTIVE – Can you match the indicator with the substance it indicates?

Note to Instructor – There are many different indicators and tests, but certain indicators can identify specific substances.

ADVANCE PREPARATION Material List 1.

Material Observation sheet 4

Number Required 1 per learner

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35 2.

Pens or pencils

1 per learner

Things to do Not Applicable Safety Precautions Not Applicable

SESSION Link to known information/ previous activity We explored different methods of identifying acids/bases and other substances today. Now let us try to match each indicator with the substance it indicates.

Procedure Instruct each learner to unfold Observation sheet 4 so that ABL 4.2 is visible. Ask them to only fill in the table for ABL 4.2. (Instructor answer key: Red litmus – Calcium hydroxide; Phenolphthalein-Hydrochloric acid; Milky water-Carbon dioxide; Pop sound-Hydrogen gas).

UNDERSTANDING THE ACTIVITY Leading questions 1. Which of the indicators indicate which substance?

Discussion and Explanation 1. Read from Observation sheet 4.2 (Confirm using answer key)

KEY MESSAGES 

There are specific indicators for different substances

LEARNING CHECK Ask learners to list the key things they have learnt. Guide them to the key messages listed and then put up the chart of key messages. If you have time during the class, make up a small game, quiz or match the following as a learning check. This may have to be done as part of advance preparation Time: 10 min

ABL 4.3 LEARNING OBJECTIVE – Can you match the indicator with the substance it indicates?

Note to Instructor – There are many different indicators and tests, but certain indicators can identify specific substances.

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ADVANCE PREPARATION Material List 1.

Material Observation sheet 4

Number Required 1 per learner

2.

Pens or pencils

1 per learner

Things to do Not Applicable Safety Precautions Not Applicable

SESSION Link to known information/ previous activity We now know that there are specific indicatorsfor certain substances. Let’s try to identify how acids and bases behave when they are subjected to different test.

Procedure Instruct each learner to unfold Observation sheet 4 so that ABL 4.3 is visible. Ask them to only fill in the table for ABL 4.3.

Instructor answer key: Test Taste Litmus Phenolphthalein Action with metals Action on metallic carbonates Action with acids Action with bases Action with metallic oxides Action with non-metallic oxides

Acid

Base Sour taste Bitter taste Turns blue litmus red Turns red litmus blue Becomes colourless Turns pink Produces hydrogen gas Generally do not react Produces carbon dioxide Generally do not react gas Generally do not react Neutralization – Produces salt and water Neutralization – Produces Generally do not react salt and water Neutralization – Produces Generally do not react salt and water Generally do not react Neutralization – Produces salt and water

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UNDERSTANDING THE ACTIVITY Leading questions 1. Which of the indicators indicate which substance?

Discussion and Explanation 1. Read from Observation sheet 4.2 (Confirm using answer key)

KEY MESSAGES 

There are specific indicators for different substances

LEARNING CHECK Ask learners to list the key things they have learnt. Guide them to the key messages listed and then put up the chart of key messages. If you have time during the class, make up a small game, quiz or match the following as a learning check. This may have to be done as part of advance preparation

REFERENCES: 1) National Council of Educational Research and Training, Class VII, December 2012 2) National Council of Educational Research and Training, Class X, November 2012

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38 APPENDIX Observation sheet 1: How do substances taste?

Name: Class: School: Substance name: Caution: 1. Do not taste anything unless asked to do so by instructor 2. Do not touch anything unless asked to do so by instructor

Substance

Taste(sour/bitter/salty/any Does blue litmus paper other taste ) change to red?

Does red litmus paper change to blue?

Lemon juice Vinegar Sugar Common salt Baking soda solution

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Observation sheet 2: Effect of acids on metals Name: Class: School: Substance name: Caution: 3. Do not handle any materials or do this activity without the supervision of the instructor 4. Use gloves and goggle

Dil.HCl Zn (Zinc)

Mg (Magnesium)

Cu (Copper)

Reaction with metal piece Effect on the lit matchstick Reaction with metal piece Effect on the lit matchstick Reaction with metal piece Effect on the lit matchstick

Chemical Equations:

General Form:

Equation for your metal-acid pair:

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Observation sheet 3: How do acids and bases react with each other?

Name: Class: School: Substance name: Caution: 5. Do not handle any materials or do this activity without the supervision of the instructor 6. Use gloves and goggle

Obs No. 1 2 3 4 5 6 7 8 9 10 INFERENCES 1 2

Description Amount of dilute NaOH in ml Color of solution after adding phenolphthalein With litmus test, is the medium acidic, basic or neutral?

HCl drop [ ] when solution colour change occurs With litmus test, is the medium acidic, basic or neutral?

No of excess drops after solution colour change happens With litmus test, is the medium acidic, basic or neutral?

Color of solution after excess HCl has been added NaoH drop [ ] when colour reappears With litmus test, is the medium acidic, basic or neutral?

When phenolphthalein colour is pink, what colour will litmus test show?

When phenolphthalein is colorless, what colour will litmus test show?

Chemical Equations:

General Form:

Equation for your metal-acid pair:

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Observation

41 Observation sheet 4: Is the solution acidic or basic?

Name: Class: School: ABL 4.1 – Fill in the table below: Test

A

B

C

D

ABL 4.2 – Draw lines to match indicators in Column A with substances in Column B: Column A (Indicators)

Column B (Substances)

1. Red Litmus

a) Hydrogen gas

2. Phenolphthalein

b) Hydrochloric acid

3. Milky water

c) Calcium hydroxide

4. Pop sound

d) Carbon dioxide

ABL 4.3 – Fill in the table below to identify how acids and bases behave in each test: Test

Acid

Base

Taste Litmus Phenolphthalein Action with metals Action on carbonates Action with acids Action with bases Action with metallic oxides Action with non-metallic oxides

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Chart 1.3: Can we find acids and bases around us?

Name: Class: School:

Did you Know?

Acidic Substance Scientific Name Vinegar Acetic acid Ant’s sting Formic acid Citrus fruits such as Citric acid, Ascorbic acid oranges, lemons etc.

(Vitamin C) Curd Lactic acid Spinach Oxalic acid Amla (Gooseberry) Ascorbic acid (Vitamin C) Tamarind, grapes, unripe Tartaric acid mangoes, etc.., Basic Substance Scientific Name Lime water Calcium hydroxide Window cleaner Ammonium hydroxide Soap Sodium hydroxide/ potassium hydroxide Milk of magnesia Magnesium hydroxide

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Chart 2.1: Effect of acids on metals Name: Class: School:

Acid + Metalďƒ Salt + Hydrogen gas

Dil. HCl

Zn Forms zinc chloride and liberates hydrogen

Mg Cu Forms Does not react magnesium with dilute acid chloride and liberates hydrogen

Equations for reaction of metals with dilute hydrochloric acid:

1. Mg(s) + 2HCl(aq) -->MgCl2(aq) + H2(g)

2. Zn(s) + 2HCl(aq) -->ZnCl2(aq) + H2(g) 3. Cu(s) + HCl(aq) --> No reaction

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Chart 2.2: Effect of acids on metal cabonates Name: Class: School:

Acid + Metal Carbonate Salt + Water + Carbon dioxide gas

 Lime water becomes milky because carbon dioxide reacts with lime water to produce a new salt – calcium carbonate – which is white in colour:

Ca(OH)2 (aq) + CO2 (g) ----------> CaCO3 (s)+ H2O(l)  Milkiness of lime water disappears after some time because calcium carbonate now starts reacting with carbon dioxide to produce another substance – calcium bicarbonate – which is soluble in lime water:

CaCO3 (s) + H2O(l) + CO2 (g) ---------->Ca(HCO3)2(aq)

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Table 3.1: How do acids and bases react with each other?

Name: Class: School:

Acid + Baseďƒ Salt + Water

 The reaction between and acid and base to give salt and water is known as a neutralization reaction:

NaOH(aq) + HCl(aq) ---------->NaCl (Aq)+ H2O(l)

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