Solutions to NCERT Class 10 Science Chapter 2 Acids, Bases and Salts

Students, welcome to Chapter 2 Acids, Bases and Salts.  We’ve compiled all the solutions to in-text questions, exercises, group activities and in-text activities in one easy-to-access place for your convenience. Our solutions are designed to ignite your curiosity, making learning fun and engaging. Additionally, we’ve included an extra set of problems to help you excel in your exams! You’ll also appreciate the vibrant illustrations we’ve added. Happy studying!

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Solutions to In Text Questions of NCERT Class 10 Science Chapter 2 Acids, Bases and Salts

Page 18:

1. You have been provided with three test tubes. One of them contains distilled water and the other two contain an acidic solution and a basic solution, respectively. If you are given only red litmus paper, how will you identify the contents of each test tube?
Answer:
The following steps are to be carried out:

• One drop of the three solutions is poured on litmus paper separately.
• The solution which turns red litmus blue is called a basic solution.
• Now divide the litmus paper which has turned blue into two parts.
• Pour a drop of the remaining two solutions, one on the first part and another on the second part of the blue litmus paper.
• The solution that turns blue litmus red will be the acidic solution.
• The solution which does not change the colour of blue litmus will be the distilled water.

Page 22:

1. Why should curd and sour substances not be kept in brass and copper vessels?
Answer:
Curd and sour substances contain acids which react with the metal in brass and copper vessel to form salt and hydrogen gas. This causes corrosion and the toxic salts thus formed can cause food poisoning. Hence, curd and sour substances should not be kept in brass and copper vessels.

2. Which gas is usually liberated when an acid reacts with a metal? Illustrate with an example. How will you test for the presence of this gas?
Answer:
When an acid reacts with a metal, hydrogen gas is evolved. For example, zinc metal reacts with hydrochloric acid to form zinc chloride and hydrogen gas:
Zn + 2HCl –> ZnCl₂ + H₂
The presence of hydrogen gas can be tested by holding a burning candle near the gas which then burns with a popping sound.

3. Metal compound A reacts with dilute hydrochloric acid to produce effervescence. The gas evolved extinguishes a burning candle. Write a balanced chemical equation for the reaction if one of the compounds formed is calcium chloride.
Answer:
The gas evolved causes effervescence and extinguishes a burning candle, hence it is carbon dioxide. It is given that one of the compounds is calcium chloride. Hence the metal compound A is calcium carbonate. The balanced chemical equation for the reaction is:
CaCO₃ (s) + 2HCl (aq) → CaCl₂( aq) + CO₂ (g) + H₂O (l)

Page 25:

1. Why do HCl, HNO₃, etc., show acidic characters in aqueous solutions while solutions of compounds like alcohol and glucose do not show acidic character?
Answer:
HCl, HNO₃, etc generate a lot of H⁺ ions in aqueous solutions and hence show strong acidic characters. While compounds like alcohol and glucosecontain hydrogen, they do not generate H⁺ ions in aqueous solutions and hence, do not show acidic character.

2. Why does an aqueous solution of an acid conduct electricity?
Answer:
An aqueous solution of an acid conduct electricity because of the presence of free H⁺ ions in the solution. The acid generates H⁺ cations and anions in aqueous solution and due to the presence of these free ions, the solution conducts electricity.

3. Why does dry HCl gas not change the colour of the dry litmus paper?
Answer:
HCl generates H⁺ or H₃O⁺ ions, which are responsible for turning blue litmus to red, only in aqueous solution. Hence, dry HCl gas cannot generate H⁺ or H₃O⁺ ions and colour of dry litmus paper does not change.

4. While diluting an acid, why is it recommended that the acid should be added to water and not water to the acid?
Answer:
The process of dissolving an acid or a base in water is a highly exothermic one. If water is added to a much larger amount of 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. Hence, acid should be added to water drop by drop and not vice versa.

5. How is the concentration of hydronium ions (H₃O⁺) affected when a solution of an acid is diluted?
Answer:
Initially there is fixed number of hydronium ions present in the solution. When a solution of an acid is diluted, the hydronium ions (H₃O⁺) per volume of the solution decreases. Hence, the concentration of hydronium ions (H₃O⁺) decreases.

6. How is the concentration of hydroxide ions (OH^–) affected when excess base is dissolved in a solution of sodium hydroxide?
Answer:
When excess base is dissolved in a solution of sodium hydroxide, the concentration of hydroxide ions (OH^–) will increase. This is because the excess base will generate more OH^– ions in the solution.

Page 28:

1. You have two solutions, A and B. The pH of solution A is 6 and pH of solution B is 8. Which solution has more hydrogen ion concentration? Which of this is acidic and which one is basic?
Answer:
Solution A has a lower pH of 6 which indicates that it is acidic and hence has more hydrogen ion concentration. Solution B has a pH of 8 which indicates that it is basic and hence has lower hydrogen ion concentration.

2. What effect does the concentration of H⁺(aq) ions have on the nature of the solution?
Answer:
The concentration of H⁺(aq)ions decide whether the solution is acidic or basic. If the concentration of H⁺(aq)ions increases, then the solution will become acidic and if the concentration of H⁺(aq)ions decreases, then the solution will become basic.

3. Do basic solutions also have H⁺(aq) ions? If yes, then why are these basic?
Answer:
Yes, basic solutions also have H⁺(aq) ions. However, the number of hydroxide(OH^–) are greatee in number and hence the solutions are basic.

4. Under what soil condition do you think a farmer would treat the soil of his fields with quick lime (calcium oxide) or slaked lime (calcium hydroxide) or chalk (calcium carbonate)?
Answer:
If the soil is acidic in nature then the farmer would treat the soil with basic quick lime (calcium oxide) or slaked lime (calcium hydroxide) or chalk (calcium carbonate) to neutralise the harmful effect of the acid.

Page 33:

1. What is the common name of the compound CaOCl₂?
Answer:
The common name of the compound CaOCl₂ is bleaching powder.

2. Name the substance which on treatment with chlorine yields bleaching powder.
Answer:
The substance which on treatment with chlorine yields bleaching powder is calcium hydroxide or slaked lime.

3. Name the sodium compound which is used for softening hard water.
Answer:
Sodium carbonate is the compound which is used for softening hard water.

4. What will happen if a solution of sodium hydrocarbonate is heated? Give the equation of the reaction involved.
Answer:
If a solution of sodium hydrocarbonate is heated it will form sodium carbonate, water and carbon dioxide gas. The reaction equation is as follows:
2NaHCO₃ + Heat —> Na₂CO₃ + H₂O + CO₂

5. Write an equation to show the reaction between Plaster of Paris and water.
Answer:
The required equation is:
CaSO₄.1/2H₂O + 1 1/2 H₂O —> CaSO₄.2H₂O

Solutions to Exercises (Page No 34) of NCERT Class 10 Science Chapter 2 Acids, Bases and Salts

1. A solution turns red litmus blue, its pH is likely to be

(a) 1
(b) 4
(c) 5
(d) 10

Answer: (d) 10

Since the solution turns red litmus blue, it is basic. Therefore, its pH is likely to be 10 since pH of a basic solution > 7.

2. A solution reacts with crushed egg-shells to give a gas that turns lime-water milky. The solution contains

(a) NaCl
(b) HCl
(c) LiCl
(d) KCl

Answer: (b) HCl

Egg shells contains calcium carbonate (CaCO₃), which on reaction with HCl solution gives out carbon dioxide gas which turns lime water milky.

CaCO₃ + HCl —> CaCl₂ + H₂O + CO₂

3. 10 mL of a solution of NaOH is found to be completely neutralised by 8 mL of a given solution of HCl. If we take 20 mL of the same solution of NaOH, the amount HCl solution (the same solution as before) required to neutralise it will be

(a) 4 mL
(b) 8 mL
(c) 12 mL
(d) 16 mL

Answer: (d) 16 mL

10 mL of a solution of NaOH is found to be completely neutralised by 8 mL of HCl solution.

Therefore, 20 mL of the solution of NaOH will be completely neutralised by (8/10× 20) mL = 16 mL.

4. Which one of the following types of medicines is used for treating indigestion?

(a) Antibiotic
(b) Analgesic
(c) Antacid
(d) Antiseptic

Answer: (c) Antacid

During indigestion the stomach produces too much acid and this causes pain and irritation. To neutralise this excess acid, people use bases called antacids.

5. Write word equations and then balanced equations for the reaction taking place when

(a) dilute sulphuric acid reacts with zinc granules.
(b) dilute hydrochloric acid reacts with magnesium ribbon.
(c) dilute sulphuric acid reacts with aluminium powder.
(d) dilute hydrochloric acid reacts with iron filings.

Answer:

(a) dilute sulphuric acid reacts with zinc granules.

Dilute sulphuric acid + zinc → Zinc Sulphate + Hydrogen Gas

H₂SO₄(aq) + Zn → ZnSO₄(aq) + H₂(g)

(b) dilute hydrochloric acid reacts with magnesium ribbon.

Dilute Hydrochloric + Magnesium → Magnesium Chloride + Hydrogen Gas

2HCl(aq) + Mg → MgCl₂(aq) + H₂(g)

(c) dilute sulphuric acid reacts with aluminium powder.

Dilute Sulphuric Acid + Aluminium → Aluminium Sulphate + Hydrogen Gas

3H₂SO₄(aq) + 2Al(s) → Al₂(SO₄)₃(aq) + 3H₂(g)

(d) dilute hydrochloric acid reacts with iron filings.

Dilute Hydrochloric Acid + Iron → Ferrous Chloride + Hydrogen Gas

6HCl(aq) + 3Fe(s) → 3FeCl₂(aq) + 3H₂(g)

6. Compounds such as alcohols and glucose also contain hydrogen but are not categorised as acids. Describe an Activity to prove it.
Answer:

Aim: To prove using an activity that alcohols and glucose contain hydrogen but are not identified as acids.

Materials Required: Hydrochloric acid solution, alcohol, glucose, two 100 mL beakers, four irons nails, two pieces of cork, two 6 V batteries, two bulbs.

Procedure:

(i) Two nails are fixed on the first cork.

(ii) The cork is placed in two 100 mL beakers.

(iii) The nails are connected to the opposite terminals of a 6 V battery through a bulb and a switch.

(iv) Now pour dilute HCl solution in the beaker and switch on the current. Note the observations.

(v) Repeat the above steps in a separate beaker with alcohol or glucose solution and note the observations.

Observations:

• The bulb glows in case of the dilute HCl solution.
• The bulb does not glow in case of the alcohol or glucose solutions.

Conclusions:

• The electric current is carried through the acidic solution by ions.
• In the first case, electric current passes through the circuit and the bulb glows indicating that acids such as HCl generate H⁺ ions in aqueous solution. Hence, they are categorised as acids.
• In the second case, electric current does not pass through the solution and the bulb does not glow indicating that alcohol and glucose do not generate H⁺ ions in aqueous solution. Hence, they are not categorised as acids.

7. Why does distilled water not conduct electricity, whereas rain water does?
Answer:
Distilled water does not conduct electricity due to the absence of free ions. Rain water conducts electricity because it has dissolved salts and acids in it which dissociates into free ions. The free ions enable rainwater to conduct electricity.

8. Why do acids not show acidic behaviour in the absence of water?
Answer:
The acidic behaviour of acids is due to generation of H⁺ ions, which can only happen in a solution of the acid in water. Hence, acids do not form H⁺ ions in the absence of water and do not show acidic behaviour.

9. Five solutions A, B, C, D and E when tested with universal indicator showed pH as 4,1,11,7 and 9, respectively. Which solution is

(a) neutral?
(b) strongly alkaline?
(c) strongly acidic?
(d) weakly acidic?
(e) weakly alkaline?

Arrange the pH in increasing order of hydrogen-ion concentration.

Answer:

(a) Solution D with pH 7 is neutral.

(b) Solution C with pH 11 is strongly alkaline.

(c) Solution B with pH 1 is strongly acidic.

(d) Solution A with pH 4 is weakly acidic.

(e) Solution E with pH 9 is weakly alkaline.

Hydrogen-ion concentration increases as the solution becomes more and more acidic. Therefore, the pH in increasing order of hydrogen-ion concentration is as follows:

pH 11 < pH 9 < pH 7 < pH 4 < pH 1

10. Equal lengths of magnesium ribbons are taken in test tubes A and B. Hydrochloric acid (HCl) is added to test tube A, while acetic acid (CH3 COOH) is added to test tube B. Amount and concentration taken for both the acids are same. In which test tube will the fizzing occur more vigorously and why?
Answer:
An acid reacts with metal to form salt and hydrogen gas is evolved. Since hydrochloric acid (HCl) is a strong acid, it will react strongly with magnesium and a lot of hydrogen will be evolved and fizzing will occur more vigorously. Since acetic acid is a weaker acid, not much hydrogen will be evolved on reaction with magnesium and fizzing will occur less vigorously.

11. Fresh milk has a pH of 6. How do you think the pH will change as it turns into curd? Explain your answer.
Answer:
Lactic acid is formed when fresh milk turns into curd. Due to formation of the acid the pH will become lesser than 6.

12. A milkman adds a very small amount of baking soda to fresh milk.

(a) Why does he shift the pH of the fresh milk from 6 to slightly alkaline?
(b) Why does this milk take a long time to set as curd?

Answer:

(a) He shifts the pH of the fresh milk from 6 to slightly alkalineto neutralize the acidic nature of milk and thus increases the time for the milk to turn into acidic curd.

(b) Since the nature of the milk is basic, the acids produced are neutralized by the base and hence it takes a long time for milk to turn acidic and form curd.

13. Plaster of Paris should be stored in a moisture-proof container. Explain why?
Answer:
Plaster of Paris mixes with water and form gypsum to form a hard solid mass. Hence, its functionality is lost.

14. What is a neutralisation reaction? Give two examples.
Answer:
The reaction between an acid and a base to give salt and water is known as neutralisation reaction. Two examples are:

NaOH(aq) + HCl(aq) —> NaCl(aq) + H₂O(l)

2NaOH(aq) + H₂SO₄(aq) —> Na₂SO₄(aq) + H₂O(l)

15. Give two important uses of washing soda and baking soda.
Answer:
Two important uses of washing soda are as follows:

(i) It is used in glass, soap and paper industries.

(ii) It is used for removing permanent hardness of water.

Two important uses of baking soda are as follows:

(i) It is used as an ingredient in antacids.

(ii) It is also used in soda-acid fire extinguishers.

Solutions to Group Activity of NCERT Class 10 Science Chapter 2 Acids, Bases and Salts

(I) Prepare your own indicator

• Crush beetroot in a mortar.
• Add sufficient water to obtain the extract.
• Filter the extract by the procedure learnt by you in earlier classes.
• Collect the filtrate to test the substances you may have tasted earlier.
• Arrange four test tubes in a test tube stand and label them as A,B,C and D. Pour 2 mL each of lemon juice solution, soda-water, vinegar and baking soda solution in them respectively.
• Put 2-3 drops of the beetroot extract in each test tube and note the colour change if any. Write your observation in a Table.
• You can prepare indicators by using other natural materials like extracts of red cabbage leaves, coloured petals of some flowers such as Petunia, Hydrangea and Geranium.

(II) Preparing a soda-acid fire extinguisher

The reaction of acids with metal hydrogencarbonates is used in the fire extinguishers which produce carbon dioxide.

• Take 20 mL of sodium hydrogencarbonate (NaHCO₃) solution in a wash-bottle.
• Suspend an ignition tube containing dilute sulphuric acid in the wash-bottle (Fig. 2.10).
• Close the mouth of the wash-bottle.
• Tilt the wash-bottle so that the acid from the ignition tube mixes with the sodium hydrogencarbonate solution below.
• You will notice discharge coming out of the nozzle.
• Direct this discharge on a burning candle. What happens?

Answer:

Solution to Group Activity

Solutions to All In-text Activities of NCERT Class 10 Science Chapter 2 Acids, Bases and Salts

1. Complete Activity 2.1 (Page 18).

• Collect the following solutions from the science laboratory hydrochloric acid (HCl), sulphuric acid (H₂ SO₄), nitric acid (HNO₃), acetic acid (CH₃COOH), sodium hydroxide (NaOH), calcium hydroxide [Ca(OH)₂ ], potassium hydroxide (KOH), magnesium hydroxide [Mg(OH)₂], and ammonium hydroxide (NH₄OH).
• Put a drop of each of the above solutions on a watch-glass one by one and test with a drop of the indicators shown in Table 2.1.
• What change in colour did you observe with red litmus, blue litmus, phenolphthalein and methyl orange solutions for each of the solutions taken?
• Tabulate your observations in Table 2.1.

Answer:

Solution to Activity 2.1

2. Complete Activity 2.2 (Page 18).

• Take some finely chopped onions in a plastic bag along with some strips of clean cloth. Tie up the bag tightly and leave overnight in the fridge. The cloth strips can now be used to test for acids and bases.
• Take two of these cloth strips and check their odour.
•  Keep them on a clean surface and put a few drops of dilute HCl solution on one strip and a few drops of dilute NaOH solution on the other.
• Rinse both cloth strips with water and again check their odour.
• Note your observations.
• Now take some dilute vanilla essence and clove oil and check their odour.
• Take some dilute HCl solution in one test tube and dilute NaOH solution in another. Add a few drops of dilute vanilla essence to both test tubes and shake well. Check the odour once again and record changes in odour, if any.
• Similarly, test the change in the odour of clove oil with dilute HCl and dilute NaOH solutions and record your observations.
  
  

Answer:

Solution to Activity 2.2

3. Complete Activity 2.3 (Page 19).

CAUTION: This activity needs the teacher’s assistance.

• Set the apparatus as shown in Fig. 2.1.
• Take about 5 mL of dilute sulphuric acid in a test tube and add a few pieces of zinc granules to it.
• What do you observe on the surface of zinc granules?
• Pass the gas being evolved through the soap solution.
• Why are bubbles formed in the soap solution?
• Take a burning candle near a gas filled bubble.
• What do you observe?
• Repeat this Activity with some more acids like HCl, HNO₃ and CH₃COOH.
• Are the observations in all the cases the same or different?

Answer:

Solution to Activity 2.3

4. Complete Activity 2.4 (Page 20).

• Place a few pieces of granulated zinc metal in a test tube.
• Add 2 mL of sodium hydroxide solution and warm the contents of the test tube.
• Repeat the rest of the steps as in Activity 2.3 and record your observations.

Answer:

Solution to Activity 2.4

5. Complete Activity 2.5 (Page 20).

• Take two test tubes, label them as A and B.
• Take about 0.5 g of sodium carbonate (Na₂CO₃) in test tube A and about 0.5 g of sodium hydrogencarbonate (NaHCO₃) in test tube B.
• Add about 2 mL of dilute HCl to both the test tubes.
• What do you observe?
• Pass the gas produced in each case through lime water (calcium hydroxide solution) as shown in Fig. 2.2 and record your observations.

Answer:

Solution to Activity 2.5

6. Complete Activity 2.6 (Page 21).

• Take about 2 mL of dilute NaOH solution in a test tube and add two drops of phenolphthalein solution.
• What is the colour of the solution?
• Add dilute HCl solution to the above solution drop by drop.
• Is there any colour change for the reaction mixture?
• Why did the colour of phenolphthalein change after the addition of an acid?
• Now add a few drops of NaOH to the above mixture.
• Does the pink colour of phenolphthalein reappear?
• Why do you think this has happened?

Answer:

Solution to Activity 2.6

7. Complete Activity 2.7 (Page 21).

• Take a small amount of copper oxide in a beaker and add dilute hydrochloric acid slowly while stirring.
• Note the colour of the solution. What has happened to the copper oxide?

Answer:

Solution to Activity 2.7

8. Complete Activity 2.8 (Page 22).

• Take solutions of glucose, alcohol, hydrochloric acid, sulphuric acid, etc.
•  Fix two nails on a cork, and place the cork in a 100 mL beaker.
• Connect the nails to the two terminals of a 6 volt battery through a bulb and a switch, as shown in Fig. 2.3.
• Now pour some dilute HCl in the beaker and switch on the current.
• Repeat with dilute sulphuric acid.
• What do you observe?
• Repeat the experiment separately with glucose and alcohol solutions. What do you observe now?
• Does the bulb glow in all cases?

Answer:

Solution to Activity 2.8

9. Complete Activity 2.9 (Page 23).

• Take about 1g solid NaCl in a clean and dry test tube and set up the apparatus as shown in Fig. 2.4.
• Add some concentrated sulphuric acid to the test tube.
• What do you observe? Is there a gas coming out of the delivery tube?
• Test the gas evolved successively with dry and wet blue litmus paper.
• In which case does the litmus paper change colour?
• On the basis of the above Activity, what do you infer about the acidic character of: (i) dry HCl gas (ii) HCl solution?

Answer:

Solution to Activity 2.9

10. Complete Activity 2.10 (Page 24).

• Take 10 mL water in a beaker.
• Add a few drops of concentrated H₂SO₄ to it and swirl the beaker slowly.
• Touch the base of the beaker.
• Is there a change in temperature?
• Is this an exothermic or endothermic process?
• Repeat the above Activity with sodium hydroxide pellets and record your observations.

Answer:

Solution to Activity 2.10

11. Complete Activity 2.11 (Page 26).

• Test the pH values of solutions given in Table 2.2.
• Record your observations.
• What is the nature of each substance on the basis of your observations?

Answer:

Solution to Activity 2.11

12. Complete Activity 2.12 (Page 27).

• Put about 2 g 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 universal indicator paper.
• What can you conclude about the ideal soil pH for the growth of plants in your region?

Answer:

Solution to Activity 2.12

13. Complete Activity 2.13 (Page 28).

• Write the chemical formulae of the salts given below. Potassium sulphate, sodium sulphate, calcium sulphate, magnesium sulphate, copper sulphate, sodium chloride, sodium nitrate, sodium carbonate and ammonium chloride.
• Identify the acids and bases from which the above salts may be obtained.
• Salts having the same positive or negative radicals are said to belong to a family. For example, NaCl and Na₂SO₄ belong to the family of sodium salts. Similarly, NaCl and KCl belong to the family of chloride salts. How many families can you identify among the salts given in this Activity?

Answer:

Solution to Activity 2.13

14. Complete Activity 2.14 (Page 29).

• Collect the following salt samples – sodium chloride, potassium nitrate, aluminium chloride, zinc sulphate, copper sulphate, sodium acetate, sodium carbonate and sodium hydrogencarbonate (some other salts available can also be taken).
• Check their solubility in water (use distilled water only).
• Check the action of these solutions on litmus and find the pH using a pH paper.
• Which of the salts are acidic, basic or neutral?
• Identify the acid or base used to form the salt.
• Report your observations in Table 2.4.

Answer:

Solution to Activity 2.14

15. Complete Activity 2.15 (Page 32)

• Heat a few crystals of copper sulphate in a dry boiling tube.
• What is the colour of the copper sulphate after heating?
• Do you notice water droplets in the boiling tube? Where have these come from?
• Add 2-3 drops of water on the sample of copper sulphate obtained after heating.
• What do you observe? Is the blue colour of copper sulphate restored?

Answer:

Solution to Activity 2.15

Extra Questions to Complement Solutions to NCERT Class 10 Science Chapter 2 Acids, Bases and Salts

Very Short Answer Type:

1. Sodium chloride is an acidic, basic or neutral salt?
Answer:
Sodium chloride is a neutral salt.

2. What is an aqueous solution of sodium chloride called?
Answer:
Brine.

3. Sodium hydrogencarbonate is an acidic, basic or neutral salt?
Answer:
Basic salt.

4. Give the formula of washing soda.
Answer:
Na₂CO₃.10H₂O

5. What is the chemical formula of gypsum?
Answer:
CaSO₄.2H₂O

6. What is the formula of blue vitriol?
Answer:
CuSO₄.5H₂O

7. What is the colour of anhydrous copper sulphate?
Answer:
White.

8. Which gas is evolved at anode in chlor-alkali process?
Answer:
Chlorine.

9. What is the colour of pure water on pH paper?
Answer:
Green.

10. What is the colour change of turmeric in contact with soap?
Answer:
Red.

Multiple Choice Questions (MCQ):

1. Aqueous solution of CH₃COONa has a pH of:

(A) >7
(B) <7
(C) = 7
(D) pH of a salt cannot be measured

Answer: (A) >7

CH₃COONa dissolves in water to form weak acetic acid CH₃COOH and strong sodium hydroxide (NaOH) base. Therefore, its pH must be > 7.

2. Which of the following is used as an ingredient in antacids?

(A) Baking soda
(B) Washing soda
(C) Bleaching powder
(D) Sodium hydroxide

Answer: (A) Baking soda

3. Which of the following is used in soda-acid fire extinguishers?

(A) Baking soda
(B) Washing soda
(C) Bleaching powder
(D) Sodium hydroxide

Answer: (A) Baking soda

4. Borax contains which of the following elements?

(A) Ca
(B) Na
(C) Fe
(D) Al

Answer: (B) Na

5. Common salt is used as a raw material for making which of the following:

(A) Sodium hydroxide
(B) Baking soda
(C) Gypsum
(D) Washing soda

Answer: (A), (B) and (D)

6. Which of the following solutions does not conduct electricity?

(A) Brine
(B) Glucose in water
(C) Dilute hydrochloric acid in water
(D) Sodium hydroxide in water

Answer: (B) Glucose in water

Glucose does not form ions in water. Hence, it does not conduct electricity.

The rest of the options all form ions in water and hence conducts electricity.

7. Which of the following is the equivalent of H₃O⁺?

(A) H⁺
(B) H₂O
(C) H⁺(aq)
(D) H₃O

Answer: (C) H⁺(aq)

8. Which of the following acids is weaker than the other three?

(A) H₂CO₃
(B) HCl
(C) HNO₃
(D) H₂SO₄

Answer: (A) H₂CO₃

9. Which of the following is a non-metallic oxide?

(A) CuO
(B) SO₂
(C) MgO
(D) FeO

Answer: (B) SO₂

Sulphur is a non-metal, hence sulphur dioxide (SO₂) is a non-metallic oxide.

10. Which of the following is not an alkali?

(A) NaOH
(B) KOH
(C) Ca(OH)₂
(D) Zn(OH)₂

Answer: (D) Zn(OH)₂

Alkalis are water soluble bases. The only base that is not soluble in water here is Zn(OH)₂. Therefore, it is not an alkali.

Short Answer Type:

1. If excess 1 M NaOH is mixed with 1 M CH₃COOH would the pH of the solution be acidic, basic or neutral? Why?
Answer:
NaOH is a strong base and CH₃COOH is a weak acid. Hence, if equal concentrations of NaOH and CH₃COOH are mixed, the pH of the solution will be basic because more OH^– ions will be formed than H⁺ ions.

2. Why is lemon juice suitable for cleaning tarnished copper vessels?
Answer:
Lemon juice in acidic which dissolves the basic copper carbonate formed on tarnished copper vessels via neutralisation reaction. Hence, it is suitable for cleaning the tarnished copper vessels.

3. Describe how chlorine gas and hydrogen gas are formed from sodium chloride?
Answer:
When electricity is passed through an aqueous solution of sodium chloride (called brine), it decomposes to form sodium hydroxide, chlorine gas and hydrogen gas. The process is called the chlor-alkali process because of the products formed – chlor for chlorine and alkali for sodium hydroxide. 2NaCl(aq) + 2H₂O(l) → 2NaOH(aq) + Cl₂(g) + H₂(g)

4. Copper oxide is a basic oxide. Explain with an example.
Answer:
Copper oxide reacts dilute hydrochloric acid to form copper (II) chloride salt and water. The reaction can be written as:
CuO + 2HCl —> CuCl₂ + H₂O
Since this is similar to the reaction between acid and a base, copper oxide is said to be a basic oxide.

5. Is the molecule Na₂CO₃.10H₂O wet?
Answer:
Despite containing water molecules, Na₂CO₃.10H₂Oappears as a solid under normal conditions. It is not wet in the sense of being a liquid or having free water on its surface. This is because the water molecules are integrated into the crystalline structure of the solid.

6. Why does dough rise when baking powder is added? Give the corresponding reaction that occurs.
Answer:
Baking powder is a mixture of baking soda and a mild edible acid such as tartaric acid. When baking powder is heated or mixed in water the following reaction takes place:
NaHCO₃ + H⁺ (from acid) —> CO₂ + H₂O + sodium salt of the acid

The carbon dioxide produced causes dough to rise.

7. Name the compound used for removing permanent hardness of water. What is it commonly known as? Give two more uses of this compound.
Answer:
The compound used for removing permanent hardness of water is sodium carbonate. It is commonly known as washing soda. Two more uses of this compound are:

(i) It is used in preparation of borax.

(ii) It is used as a cleaning agent for domestic purposes.

8. State whether the pH of the following compounds in water are greater, less than or equal to 7:

(i) NaCl
(ii) H₂CO₃
(iii) CuCl₂
(iv) HCl

Answer:

(i) NaCl: This is a neutral salt because it is made of strong base NaOH and strong acid HCl. So pH is = 7.

(ii) H₂CO₃ is a weak acid, so pH < 7.

(iii) CuCl₂ is an acidic salt because it is made of weak base Cu(OH)₂ and strong acid HCl. Hence pH < 7.

(iv) HCl is a strong acid, so pH < 7.

9. Give the reaction for producing baking soda.
Answer:

NaCl + H₂O + CO₂ + NH₃ —> NH₄Cl + NaHCO₃

10. Give two ways of determining pH of a solution.
Answer:
Two ways of determining pH of a solution are:

(i) Using paper impregnated with universal indicator.

(ii) Using pH meter.

Long Answer Type:

1. Sodium hydrogencarbonate when heated produces a compound A and a gas C in addition to water.

(i) What are A and C?
(ii) If compound A is dissolved in water, what kind of solution will it form: acidic, basic or neutral?
(iii) What will happen when the gas C is passed through lime water?
(iv) Give the common name of sodium hydrogencarbonate.

Answer:

(i) A is Sodium carbonate (Na₂CO₃) and C is carbon dioxide (CO₂).

(ii) If Na₂CO₃ is dissolved in water, strong base NaOH and weak acid H₂CO₃ is formed. Hence, the solution will be basic.

(iii) If carbon dioxide (CO₂) passed through lime water, it will turn lime water milky.

(iv) Sodium hydrogencarbonate is commonly known as baking soda.

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