Formative Assessment 
 

III. EXPERIMENTATION AND FIELD INVESTIGATION 
1. Fresh milk has a pH of 6. Explain why the pH changes as it turns into curd. (2 Marks)
A. * The pH 6 of milk is due to the casein (milk protein) which is a phospho protein and therefore milk is slightly acidic.
* During curdling, the lacto bacillus keeps growing and it breaks down the lactose (the natural sugar in milk) into lactic acid which acidifies the milk even further.
* Therefore, the pH of the milk will drop (decrease) (as the more acidic the substance the lower the pH) as it gets converted into curd.
 

2. Compounds such as alcohols and glucose contain Hydrogen but are not categorized as acids. Describe an activity to prove it. (4 Marks)
A. * Prepare solutions of glucose, alcohol, Hydrochloric acid and sulphuric acid etc.,
* Connect two different coloured electrical wires to graphite rods separately in a 100 ml beaker as shown in the figure.

* Connect free ends of the wire to 230 Volts AC plug and complete the circuit by connecting a bulb to one of the wires.
* Now pour some dilute HCl in the beaker and switch on the current.
* We observe that the bulb glows.
* Repeat activity with dilute Sulphuric acid and glucose and alcohol solutions.
* We will notice that the bulb glows only in acid solutions but not in glucose and alcohol solutions.
* Glowing of bulb indicates that there is flow of electric current through the solution.
* Acid solutions have ions and the moment of these ions in solution helps for flow of electric current through the solution.
* The positive ion (cation) present in HCl solution is H⁺. This suggests that acids produce Hydrogen ions H⁺ in solution, which are responsible for their acidic properties.
* In glucose and alcohol solution the bulb did not glow indicating the absence of H+ ions in these solutions.
* So glucose and alcohol are not categorized as acids.

3. What is meant by 'water of crystallization of a substance'? Describe an activity to show the water of crystallization. (4 Marks)
A. * "Water of crystallization" is the fixed number of water molecules chemically attached to each formula unit of a salt in its crystalline form.
e.g.: CuSO₄. 5 H₂O.

* Take few crystals of Copper sulphate in a dry test tube and heat the test tube.
* We notice water droplets on the sides of the test tube.
* The blue colour of the salt Copper sulphate turned to white due to heating.
* When crystals are moistened with water, the blue colour reappears.
 

Explanation: (Reason)
* Copper sulphate crystals which seem to be dry contain the water of crystallization, when these crystals are heated, water present in crystals is evaporated and the salt turns white.
* When the crystals are moistened with water, the blue colour reappears.
* Water of crystallization is the fixed number of water molecules present in one formula unit of a salt.
* Five water molecules are present in one formula unit of Copper sulphate.
* Chemical formula for hydrated Copper sulphate is CuSO₄. 5 H₂O.

IV. Information skills and Projects 
4. Equal lengths of magnesium ribbons are taken in test tubes A and B. Hydrochloric acid is added to test tube A, while Acetic acid is added to test tube B. Amount and concentration of both the acids is the same. In which test will the fizzing occur more vigorously and why? (2 Marks)
A. * In the testtube A fizzing occur more vigorously. This is because Hydrochloric acid is a strong acid and it contains more H₃O⁺ ions.
* The reaction in test tube A is therefore fast.
* In the test tube B added Acetic acid is a weak acid. It contains less number of H₃O⁺ ions.
* So the reaction in the test tube B is slow.

V. Communication Through Drawing, Model Making 
5. Draw a neat diagram showing acid solution in water conducts electricity. (4 Marks)

6. How do you prepare your own indicator using Beetroot? (4 Marks)
A. * Peel the skin of a beetroot.
* Cut it into small pieces. Boil it with water for some time.
* Strain it using a strainer.
* Take a small piece of a paper and dip it in the beetroot liquid for some time and then dry it.
* Now this paper can be used as a beetroot indicator.
* If this paper is dipped in the given solution the following change in colours give the pH value of the solution.
      1) pH2 - Red Colour                      
      2) pH4 - Purple Colour
      3) pH6 - Violet Colour                      
      4) pH8 - Blue Colour
      5) pH10 - Blue/Green Colour        
      6) pH12 - Green Colour
* Beetroot contains Anthocyanins and so it works as an indicator.
 

VII. Application to Daily Life, Concern to Biodiversity 

7. How does the flow of acid rain into a river make the survival of aquatic life in a river difficult. (2 Marks)
A. * Acid rain water when flows in to the river, the pH of the river water changes.
* This makes the aquatic life difficult to survive.
* The pH range suitable for aquatic survival is 7.0 to 7.8.
* Due to acid rain pH decreases.
 

8. What is Baking powder? How does it make the cake soft and spongy? (2 Marks)
A. * Baking powder is a mixture of Baking soda and Tartaric acid.
* When baking powder is heated it releases CO₂ gas due to which the cake rises and becomes soft and spongy.
 

9. Give two important uses of Washing Soda and Baking Soda. (4 Marks)
A. Uses of Washing Soda:
* Sodium carbonate (Washing Soda) is used in glass, soap and paper industries.
* It is used in the manufacture of Sodium compounds such as Borax.
Uses of Baking Soda:
* Sodium hydrogen carbonate is also ingredient in antacids. Being alkaline, it neutralizes excess acid in the stomach and provides relief.
* It is also used in soda-acid fire extinguishers.
* It is used as baking powder in confectionery items like cake, pastry etc.,
 

ACTIVITIES 

Activity: 1 
1. Collect the following samples of substances shown in the table and find out the changes in the colours of the indicators and note them in the table. (4 Marks) (AS-7)
A.

 

Activity: 2
2. What are olfactory indicators? Describe an activity to show their working. (2 Marks) (AS-3)
A. * Put some finely chopped onions in a plastic bag along with some clean cloth. Tie up the bag tightly and keep it overnight in the fridge. The cloth strips can now be used to test for acid or base.
* Check the odour of the cloth strips.
* Onion loses its smell when added with a base.
* Onion does not change its smell with an acid.
* Olfactory indicators are used to ensure participation of visually impaired students in the laboratory.
 

Activity: 2A (LAB ACTIVITY)
3. Describe the laboratory activity to prove that acids react with metals and release Hydrogen gas. (4 Marks) (AS-3)
A. Aim: To prove that acids react with metals and release Hydrogen gas.

Materials required: Test tube, delivery tube, glass through, candle, soap water, dil. HCl and Zinc granules.
Procedure:
* Set the apparatus as shown in the figure.
* Take about 10 ml of dilute HCl in a test tube and add a few Zinc granules to it.
* What do you observe on the surface of the Zinc granules?
* Pass the gas being evolved through the soap water.
* Bubbles are formed in the soap solution.
* Bring a burning candle near the gas filled bubble.
* We notice the gas evolved burns with a pop sound indicating H₂.
The chemical reaction of the above activity is:
     Acid     +   Metal →  Salt    +    Hydrogen
    2 HCl (aq)    +   Zn (s)  → ZnCl₂ (aq)   +   H₂ (g)
* Repeat the above experiment with some other acids like H₂SO₄ and HNO₃.
* From the above activities we can conclude that when acid reacts with metal H₂ gas is evolved.

ACTIVITY: 3
4. Prove with the help of an activity that metals reacts with a base and release Hydrogen.
A. * Place few granules of Zinc metal in one of the test tubes and add 10 ml of Sodium hydroxide (NaOH) solution and warm the contents of the test tube.
* Pass the gas being evolved through the soap water.
* Bubbles are formed in the soap solution.
* Bring a burning candle near the gas filled bubble.
* We notice the gas evolved burns with a pop sound indicating Hydrogen.
* In this activity the salt formed is Sodium zincate.
* The reaction is written as follows:
      2 NaOH + Zn →  Na₂ZnO₂  +  H₂
                  (Sodium Zincate)
* All metals do not react like this.

ACTIVITY: 4
5. Establish the fact that carbonates and Hydrogen carbonates react with acids to give a corresponding salt, carbon dioxide and water with the help of an activity.
A.
             
* Take two test tubes; label them as A and B.
* Take about 0.5 gm of Sodium carbonate (Na₂CO₃) in test tube A and about 0.5 gm of Sodium hydrogen carbonate (NaHCO₃) in test tube B.
* Add about 2 ml of dilute HCl to both the test tubes.
* Pass the gas produced in each case through lime water (Calcium hydroxide solution) as shown in Fig. and record your observations.
* We observe that lime water turns to milky white.
* The reactions occurring in the above activities are as follows.
      a) Na₂CO₃ (s) + 2HCl (aq) → 2 NaCl (aq) + H₂O (l) + CO₂ (g)
      b) NaHCO₃ (s) + HCl (aq)  →NaCl (aq) + H₂O (l) + CO₂ (g)
* Pass the gas evolved through lime water.
      Ca(OH)₂ (aq) + CO₂ (g) → CaCO₃  + H₂O (l)
                                       (White Precipitate)
* On passing excess Carbon dioxide the following reaction takes places:
      CaCO₃ (s) + H₂O (l) + CO₂ (g) → Ca(HCO₃)₂ (aq)
                                                    (Soluble in Water)
* Thus from the above activities you can conclude that the reaction of metal Carbonates and Hydrogen carbonates with acids give a corresponding salt, Carbon dioxide and water.

ACTIVITY: 5
6. What is neutralization? Explain neutralization through an activity. (4 Marks) (AS -3)
A. Neutralization:
The reaction of an acid with a base to give a salt and water is known as a neutralization reaction. In general, a neutralization reaction can be written as:
     Base + Acid → Salt + Water
Acid - Base reaction:
* Take about 2 ml of dilute NaOH solution in a test tube and add one drop of phenolphthalein indicator.
* The solution turns pink.
* Add dilute HCl solution to the above solution drop by drop. The Pink colour disappears.
* Now add one or two drops of NaOH to the above mixture. We notice that the pink colour reappears.
* In the above activity you observe that the pink colour disappears on adding HCl because NaOH is completely reacted with HCl.
* The effect of base is nullified by a acid. Pink colour reappears on adding a drop of NaOH because the solution becomes basic once again.
* The reaction occurring between acid and base in the above activity can be written as:
     NaOH (aq) + HCl (aq) → NaCl (aq) + H₂O (l)
* This is neutralization reaction.

Activity: 6
7. Describe an activity to show that the metal oxides are basic in nature. (4 Marks) (AS-3)
A. * Take a small amount of Copper oxide in a beaker and slowly add dilute Hydrochloric acid while stirring.
* We will notice that the Copper oxide present in the beaker dissolves in dilute HCl and the colour of the solution becomes blueish-green.
* The reason for this change is the formation of Copper chloride in the reaction.
* The general reaction between a metal oxide and an acid can be written as
     Metal Oxide + Acid → Salt + Water.
* This reaction is similar to the reaction of a base with an acid in a neutralization reaction.
* Here in this reaction metal oxide reacts with an acid giving a salt and water. This indicates that metal oxides are basic in nature.

ACTIVITY: 7
8. Perform an activity to investigate whether all compounds containing Hydrogen are acids or not.
A.

* Prepare solutions of glucose, alcohol, Hydrochloric acid and Sulphuric acid etc.
* Connect two different coloured electrical wires to graphite rods separately in a 100 ml beaker as shown in figure.
* Connect free ends of the wire to 230 Volts AC plug and complete the circuit as shown in the fig. by connecting a bulb to one of the wires.
* Now pour some dilute HCl in the beaker and switch on the current.
* Repeat activity with dilute Sulphuric acid and glucose and alcohol solutions.
* We will notice that the bulb glows only in acid solutions but not in glucose and alcohol solutions.
* Glowing of bulb indicates that there is flow of electric current through the solution
* Acid solutions have ions and the moment of these ions in solution helps for flow of electric current through the solution.
* The positive ion (cation) present in HCl solution is H⁺. This suggests that acids produce Hydrogen ions H⁺ in solution, which are responsible for their acidic properties.
* Glucose and Alcohol solution the bulb did not glow indicating the absence of H⁺ ions in these solutions. The acidity of acids is attributed to the H⁺ ions produced by them in solutions.
 

ACTIVITY: 8
9. Do acids produce ions only in aqueous solutions? Test this with an activity.
A. * Take about 1.0 gms of solid NaCl in a clean and dry test tube.
* Add some concentrated Sulphuric acid to the test tube.
* We observe a gas is coming out.
* The reaction that takes place is
      2 NaCl (s) + H₂SO₄ (l) → 2 HCl (g) ↑ + Na₂SO (s)
* Test the gas evolved successively with dry and wet blue litmus paper.
* We observe that there is no change in the colour of the dry litmus paper.
* We can conclude that dry HCl gas (Hydrogen chloride) is not an acid because, we have noticed that there is no change in colour of dry litmus paper but HCl aqueous solution is an acid because wet blue litmus paper turned into red.

* The HCl gas evolved at delivery tube dissociates in presence of water to produce Hydrogen ions.
* In the absence of water dissociation of HCl molecules do not occur.
* The dissociation of HCl in water is HCl + H₂O → H₃O⁺ + Cl ^-(aq.)
* It means acids give H₃O⁺ ions in water.

ACTIVITY: 8A
10. Explain what happens when a base is dissolved in Water. (2 Marks) (AS-3)
A. * Take different bases like NaOH, KOH, Mg(OH)₂ ... etc in different test tubes and add water to each of them respectively.
* The following reactions take place.
NaOH (s)  Na⁺ (aq.) + OH^- (aq.)
KOH(s)  K⁺ (aq.) + OH- (aq.)
Mg(OH)₂ (s)  Mg₂ (aq.) + 2 OH^- (aq.)
* We can thus conclude that on dissolving a base in water produces hydroxide (OH^-) ions.

ACTIVITY: 9
11. What do you observe when water is mixed with an acid? Describe it through an activity. (2 Marks) (AS-3)
A. * Take 10 ml water in a test tube.
* Add a few drops of concentrated H₂SO₄ to it and swirl the test tube slowly.
* Touch the bottom of the test tube.
* The bottom of the test tube is hot.
* This is an exothermic process.
 

ACTIVITY: 9A
12. What happens when water is mixed with a base? Explain your observation by an activity. (2 Marks) (AS - 3)
A. * Take 10 ml water in a test tube.
* Add a few drops of Sodium hydroxide pellets to it and swirl the test tube slowly.
* Touch the bottom of the test tube.
* The bottom of the test tube is hot.
* This is an exothermic process.
 

ACTIVITY: 10
13. Describe an activity to know whether the given acid is strong or weak. (4 Marks) (AS - 3)
A.

* A test to know whether the acid is strong or weak.
* Take two beakers A and B
* Fill the beaker A with dil.CH₃COOH (Acetic acid) and beaker B with dil. HCl (Hydrochloric acid).
* Arrange the apparatus as shown in the figure and pass electric current through the solutions in separate beakers.
* We notice that the bulb glows brightly in the HCl solution while the intensity of the bulb is low in Acetic acid solution.
* This indicates that there are more ions in HCl solution and fewer ions are present in acetic acid solution.
* More ions in HCl solution means more H₃O⁺ ions. Therefore it is a strong acid.
* Acetic acid has fewer H₃O⁺ ions and hence it is a weak acid.
 

ACTIVITY: 11
14. Test the pH value of solutions given in the table using pH paper. Record your observations in Column three of the table. Write approximate pH values in Column 4 using Universal Indicator Solution. What is the nature of each substance on the basis of your observation. (4 Marks) (AS-3)
A.

 

ACTIVITY: 12
15. With an activity explain how do you find the action of an antacid tablet? (2 Marks) (AS-3)
A. * Take dil. HCl in a beaker and add two to three drops methyl orange indicator.
* The solution turns to red colour.
* Mix the antacid tablet powder to the above solution in the beaker.
* The solution becomes neutral and the red colour of the solution disappears.
* This confirms the action of an antacid is tablet in neutralising the acid.
 

ACTIVITY: 13
16. Describe an activity to test the pH of the Soil. (2 Marks) (AS-3)
A. * Collect samples of soil from different places.
* Put about 2 gm of soil in a test tube and add 5 ml water to it.
* Shake the contents of the test tube. Filter the contents and collect the filtrate in a test tube.
* Check the pH of this filtrate with the help of a universal indicator paper.
* The colour of the Universal indicator paper reveals the pH value of the soil taken in the test tube.
 

ACTIVITY: 14
17. Identify the families of the following salts writing their formula based on their radicals. Also identify the acids and bases from which these salts are obtained.
  Potassium Sulphate, Sodium Sulphate, Calcium Sulphate, Magnesium Sulphate, Copper Sulphate, Sodium Chloride, Sodium Nitrate, Sodium Carbonate and Ammonium Chloride (4 Marks) (AS-3)
A.

 

Families of the Salts

1) Sodium family : Na₂SO₄, NaCl, NaNO₃, Na₂CO₃
2) Chloride family: NaCl, NH₄Cl
3) Sulphate family: K₂SO₄, Na₂SO₄, CaSO₄, MgSO₄, CuSO₄
4) Carbonate family: Na₂CO₃, MgCO₃, CaCO₃
 

ACTIVITY: 15
 

18. Collect the salt samples like Sodium chloride, Aluminaum chloride, Copper sulphate, sodium acetate, ammonium chloride, Sodium hydrogen carbonate and Sodium carbonate. Dissolve them in distilled water. Check the action of these Solutions with litmus papers. Find the pH using pH paper (universal indicator). Classify them into acidic, basic or neutral salts? Identify the acid and base used to form the above salts. Record your observations in a Table. (4 Marks) (AS -3)
A.

 

III. Experimentation and Field Investigation 
1. 5 C.C. of Limewater is taken in a test tube. If a drop or two of red litmus is added to it. What happens (1 Mark) (AS-3)
A. The red litmus turns to Blue colour.
 

2. One or two drops of Phenolphthalein is added to 5 C.C. of lime water taken in a test tube. What change do you observe? (1 Mark) (AS-3)
A. The solution turns to Pink colour.
 

3. What happens if 2 drops of Methyl orange is added to 5 C.C. of lime water (1 Mark) (AS-3)
A. The colour of the solution turns to Yellow.
 

4. Why is it recommended that water should be added to water but not water to acid. Explain. (4 Marks) (AS-3)
A. * The process of dissolving an acid or a base in water is an exothermic process.
* Care must be taken while mixing concentrated Nitric acid or sulphuric acid with water.
* The acid must always be added slowly to water with constant stirring.
* If water is added to a concentrated acid, the heat generated may cause the mixture to splash out and cause burns.
* The glass container may also break due to excessive local heating.
 

5. What type of process is dissolving an acid or a base in water? (1 Mark)
A. The process of dissolving an acid or a base in water is an exothermic process. 
 

IV. INFORMATION SKILLS AND PROJECTS
 

6. Mention three acids and write atleast two uses of each acid. (4 Marks) (AS-4)
A. * Sulphuric acid (H₂SO₄) , Hydrochloric acid (HCl) and Nitric Acid (HNO₃) are the three acids.
Uses of Sulphuric Acid:
* It is used in the manufacture of fertilizers.
* It is used in Car batteries.
Uses of Hydrochloric acid:
* It is used in dyeing industry.
* It is used for preparing glucose from starch.Uses of Nitric acid:
* It is used in the manufacture of explosives such as TNT (Trinitrotoluene) and TNG (Trinitroglycerine).
* It is used in the Purification of metals such as Gold and Silver.
 

7. Name any four acids and write atleast one use of each acid. (4 Marks) (AS-4)
A. Phosphoric acid, Carbonic acid, Acetic acid and Tartaric acid are the four acids.
Uses:
* Phosphoric acid: It is used in the manufacture of Phosphatic Fertilisers.
* Carbonic acid: It is commonly called Plain Soda. It is mixed with Citric acid and sugar, it is used for making soft drinks.
* Acetic acid: It is used as a table acid and for preservation of food articles.
* Tartaric acid: It is used in the manufacture of baking powder.
 

8. How do the indicators change in colour when come in touch with bases. (2 Marks) (AS-4)
A.

9. Write atleast four names of hydrated salts mentioning their formula and colour. (4 Marks) (AS-4)
A.

10. Mention four hydrated salts, their common name, chemical name and formula. (4 Marks) (AS-4)
A.

11. What are strong and weak bases. (2 Marks) (AS-4)
A. * The oxides and hydroxides of Sodium and Potassium are strong bases. They are very soluble in water.
* The oxides and hydroxides of all other metals are weak bases. They are sparing soluble in water or insoluble in water.
* Ammonium hydroxide obtained by dissolving ammonia gas in water is also a weak base.
 

12. What are strong acids. Give examples. (2 Marks) (AS-4)
A. * A strong acid is one which gives more H₃O⁺ ions in its diluted stage.
* Sulphuric acid, Hydrochloric acid and Nitric acid are strong acids because they give more H₃O⁺ ions in their diluted stage.
 

13. What are weak acids. Give examples for inorganic acids. (2 Marks) (AS-4)
A. * A weak acid is one which gives fewer H₃O⁺ ions in its diluted stage.
* Carbonic acid, Sulphurous acid, Phosphoric acid, Nitrous acid are all weak inorganic acids.
* These give fewer H₃O⁺ ions in their diluted stage.
 

14. What can you conclude about the ideal soil pH for the growth of plants in your region. (AS-4) (2 Marks)
A. * The optimum pH range for most plants is between 5.5 and 7.0
* However many plants have adopted to thrive at pH values.
 

15. Under what soil conditions a farmer would treat the soil of his field with quick lime (Calcium hydroxide) or Calcium Carbonate? (2 Marks) (AS-4)
A. If the soil is acidic in nature which is not suitable for agriculture, then the farmer would treat the soil with quick lime, or Calcium carbonate.
 

16. How is Sodium hydroxide prepared from Common Salt. (4 Marks) (AS-4)
A. Preparation of Sodium hydroxide:
* When electricity is passed through an aqueous solution of Sodium chloride (called brine), it decomposes to form Sodium hydroxide.
* The process is called the chlor-alkali process - because of the products formed chlor for chlorine and alkali for Sodium hydroxide.

* 2 NaCl (aq) + 2 H₂O (l)  → 2 NaOH (aq) + Cl₂ (g) + H₂ (g)
* Chlorine gas is given off at the anode and Hydrogen gas at the cathode.
* Sodium hydroxide solution is formed near the cathode.
* The three products produced in this process are all useful. Fig. shows the different uses of these products.

17. What does the given symbol indicate? (2 Marks) (AS-4)
                
A. This is a warning symbol on containers containing concentrated Acids and Bases.
 

V. Communication Through Drawing, Model Making 
 

18. Observe the below figure which shows variation of pH with the change in concentration of H⁺ (aq) ions and OH^- (aq) ions. (AS-5)
          
                   Variation of pH with the change in concentration
                           of H⁺ (aq) ions and OH^- (aq) ions
 

19. Who introduced the concept of pH. Why is it restricted for solutions of [H⁺] less than 1 molar. (2 Marks) (AS-5)
A. * To avoid the negative powers of H⁺ concentration in dilute acid and base solutions Sorensen introduced the concept of pH.
* Due to this pH concept may be restricted for solutions of [H⁺] less than 1 molar.
 

20. Observe the pH scale and the placement of solutions on this scale. Explain about this scale. (AS-5)
A. The pH scale is from 0 -14. The pH is an indication of concentration of H⁺. For example, at a pH of zero the hydronium ion concentration is one molar. Typically the concentrations of H⁺ in water in most solutions fall between a range of M (pH = 0) and 10^-14 M (pH = 14). Figure 8 depicts the pH scale with common solutions.

VII. Application to Daily Life, Concern to Bio Diversity 
 

21. What happens if an antacid tablet is used by a person. (4 Marks)
A. * It is very interesting to note that our stomach produces Hydrochloric acid.
* It helps in the digestion of food without harming the stomach. During in digestion the stomach produces too much acid and this causes pain and irritation.
* To get rid of this pain, people use bases called antacids.
* These antacids neutralize the excess acid in the stomach.
* Magnesium hydroxide (milk of magnesia), a mild base, is often used for this purpose.
 

22. Why living organism have a narrow pH range?
A. * Living organism can survive only in a narrow range of pH change.
* When pH of rain is less than 5.6 it is called acid rain.
* When acid rain flows to rivers, it lowers the pH of the river water, the survival of aquatic life in such rivers became difficult.
 

23. How do animals and plants play self defence through chemical warfare. What is the traditional remedy for this. (4 Marks)
A. * If you have been stung by a honey bee the bee string leaves an acid. Which causes pain and irritation.
* Use of a mild base like baking soda on the stung area gives relief.
* Stinging hair of leaves of nettle plant, inject methanoic acid causing burning pain.
* A traditional remedy is rubbing the area with the leaf of the dock plant, which often grows besides the nettle in the wild.
 

Writer : C.V. SARVESWARA SARMA