Class 10 Science Chapter 2 Acids-Bases and Salts

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Class 10 Science Chapter 2 Acids-Bases and Salts

Also, you can read the SCERT book online in these sections Solutions by Expert Teachers as per SCERT (CBSE) Book guidelines. These solutions are part of SCERT All Subject Solutions. Here we have given Assam Board Class 10 Science Chapter 2 Acids-Bases and Salts Solutions for All Subjects, You can practice these here…

Acids-Bases and Salts

Chapter – 2

GENERAL SCIENCE

TEXTUAL QUESTIONS AND ANSWERS

Page -18 

Q.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 ? 

Ans :- First we have divided the red litmus paper in to three parts. We can dip each paper in the three test tubes separately. The test tubes in which the red litmus paper turns blue is basic solution. The test tube in which red litmus paper turns light red is distilled water. The test tube in which red litmus paper has no change in colour is acidic solution. 

Page No -22 

Q.1. Why should curd and sour substances not be kept in a brass and copper vessels ? 

Ans :- Curd and sour substances contains acids and acids react with brass and copper. So curd and sour substances not be kept in a brass and copper vessels. 

Q.2. Which gas is usually liberated when an acid react with a metal. Illustrate with an example. How will you test for the presence of the gas ? 

Ans :- (i) H₂ gas is liberated when an acid reacts with a metal. 

(ii) Illustration :- Set up an apparatus. Take some Zinc granules in the test tube. Add about 5 ml dilute hydrochloric acid slowly. Soon the reaction between Zinc and hydrochloric acid starts and hydrogen gas is evolved.

(iii) Test for H₂ gas :- H₂ gas is not soluble in water. When passed through soap solution, it gets trapped into bubbles which burn with explosion. 

Q.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. 

Ans :- Since the end product is calcium chloride and the gas formed extinguishes a burning candle, it is Co₂ . The metal compound must be calcium carbonate.

Hence, the reaction between calcium carbonate and hydrochloric acid is as follows :- 

C aCO₃ + 2HCI → CaCl₂ + CO₂ + H₂O 

Page -25 

Q.1. Why do HCI, HNO₃ etc., show acidic characters in aqueous solutions while solutions of compounds like alcohol and glucose do not show acidic character ? 

Ans :- HCI, HNO₃ etc, are produced H⁺ ions in the presence of water. Therefore they show acidic characters in aqueous solutions. While alcohol and glucose do not produce H⁺ ions and therefore they do not show acidic character. 

Q.2. Why does an aqueous solution of an acid conduct electricity ? 

Ans :- Acids give ions in aqueous solution and the electric current is carried through the solution by ions. Therefore aqueous solution of an acid conduct electricity. 

Q.3. Why does dry Hcl gas not change the colour of the dry litmus paper ? 

Ans :- Dry Hcl gas does not contain H⁺ ions and hence does not change the colour of the dry litmus paper. 

Q.4. While diluting au acid, why is it recommended that the acid should be added to water and not water to the acid ? 

Ans :- 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.

Q.5. How is the concentration of hydronium ions (H₃O⁺) affected when a solution of an acid is diluted ?

Ans :- Mixing an acid with water results in decrease in the concentration of H₃O⁺ ions per unit volume. 

Q.6. How is the concentration of hydroxide ions (OH⁻) affected when excess base is dissolved in a solution of sodium hydroxide ? 

Ans :- The concentration of hydroxide ions will increase when excess base is dissolved in a solution of sodium hydroxide because the amount of hydroxide ions per unit volume increases. This happens only when base added dissolved in water. If the base is not soluble in water, the concentration of hydroxide ions remains constant. 

Page -28 

Q.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 ? 

Ans :- Solution A has more hydrogen ion concentration. Solution A is acidic and solution is basic. 

Q.2. What effect does the concentration of H⁺ (aq) ions have on the nature of the solution ? 

Ans :- Acids that give rise to more H⁺ ions are strong acids and acids that give less H⁺ ions are weak acids. 

Q.3. Do basic solutions also have H⁺ (aq) ions ? If yes, then why are these basic ? 

Ans :-  Basic solution also have H⁺ ions. But these are farless in number than OH⁻ ions. For more number of OH⁻ ions the solution is basic. 

Q.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) ? 

Ans :- When the soil become acidic farmers treat the soil fields with bases like quick lime, slaked lime or chalk. 

Page -33

Q.1. What is the common name of the compound CaOcl₂ ? 

Ans :- Bleaching powder. 

Q.2. Name the substance which on treatment with chlorine yields bleaching powder. 

Ans :- Lime water. 

Q.3. Name the sodium compound which is used for softening hard water. 

Ans :-  Sodium carbonate. 

Q.4. What will happen if a solution of sodium hydrocarbonate is heated ? Give the equation of the reaction involved. 

Ans :- Sodium hydro carronate on heating gives sodium carbonate and Co₂ gas. 2NaHCO₃ → Na₂Co₃ + Co₂+ H₂O 

Q.5. Write an equation to show the reaction between plaster of paris and water. 

Ans :- CaSO₄. ½ H₂O + 1½ H₂O → CaSO₄. 2H₂O

EXERCISES

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

(a) 1  (b) 4   (c) 5   (d) 10   

Ans :- (d) 10. 

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

(a) Nacl    (b) Hcl     (c) Licl     (d) Kcl 

Ans :- (b) Hcl. 

Q.10 ml of solution of NaOH is found to be completely neutralized 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 solution as before) required to neutralize it will be

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

Ans :- (d) 16 ml. 

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

(a) antibiotic.

(b) Analgesic. 

(c) Antacid.

(d) Antiseptic.

Ans :- (c) Antacid. 

Q.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.

(c) dilute sulphuric acid reacts with aluminium powder. 

(d) dilute hydrochloric acid reacts with iron filings. 

Ans :- (a) Dil.Sulphuric acid + zinc → zinc sulphate + Hydrogen H₂SO₄ + zn ZnSO₄ + H₂

(b) Dil hydrochloric acid + Magnesium → Magnesium chloride + Hydrogen. 

Hcl + Mg → Mgcl₂ + H₂ 

⇒ 2HCl + Mg → Mgcl₂ + H₂

(c) Aluminium powder + dil sulphuric acid → Aluminium sulphate + Hydrogen Al + H₂SO₄ → Al₂(SO₄)₃ + H₂ 

⇒ 2AI + 3H₂SO₄ → Al₂ (SO₄)₃ + H₂ 

(d) Dil. hydrochloric acid + Iron → Iron chloride + Hydrogen Hcl + Fe → FeCl₃ + H₂ 

⇒ 6Hcl + 2Fe → 2Fecl₃ +3H₂ 

Q.6. compounds such as alcohols and glucose also contain hydrogen beet are not categorised as acids. Describe an activity to prove it.

Ans :- Take solutions of glucose and alcohols in a beaker. Fix two nails on a cork and place the cork in the beaker.connect the nails to the two terminals of a 6 volt battery through a bulb and a switch. Switch on the current. The bulb does not glow. That means current does not pass through the circuit. This show that no H⁺ ions are present in the solution. This experiment shows that alcohol and glucose are not acid.

Q.7. Why does distilled water not conduct electricity, whereas rain water does? 

Ans :- There are not ions in distilled water, So distilled water not conduct electricity. But rain water contains ions and so conduct electricity. 

Q.8. Why do acids not show acidic behaviour in the absence of water ? 

Ans :- The separation of hydronium ions from acid molecules cannot occur in the absence of water. Therefore acids cannot show acidic behaviour in the absence of water. 

Q.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. 

Ans :- (a) Neutral solution is D 

(b) Strongly alkaline is C 

(c) Strongly acidic is B 

(d) Weakly acidic is A 

(e) Weakly alkaline is E 

Pᴴ values in increasing order of hydrogen ion concentration 11<9<7<4<1 

Q.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 be fizzing occur more vigorously and why ? 

Ans :-  Hydrochloric acid is stronger acid than acetic acid and reaction between magnesium ribbon and Hcl is faster than between magnesium ribbon and CH₃ COOH. So fizzing will occur more vigorously in test tube A. containing hydrochloric acid. 

Q.11. Fresh milk has a pH of 6. How do you think the Pᴴ will change as it turns into curd ? Explain your answer. 

Ans :- The Pᴴ value of fresh milk falls below 6 when it turns into curd due to the formation of lactic acid during the process. 

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

(a) Why does the 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 ? 

Ans :- (a) The milkman adds a little baking soda to fresh milk to make it slightly alkaline so that milk can be preserved for a longer time. 

(b) The lactic acid is used for neutralize the base initially and when more lactic acid is formed then the milk sets as curd. 

Q.13. Plaster of paris should be stored in a moisture-proof container. Explain why ? 

Ans :-  If plaster of paris will store in a moisture then it changes to gypsum giving a hard solid mass. Which does not have the required selting property. 

Q.14. What is a neutralisation reaction ? Give two example. 

Ans :- The reaction between an acid and a base to give a salt and water is known as neutralisation reaction.

Examples :- (i) Hcl  +  NaOH  →  Nacl  +   H₂O

                       (acid)    (Base)     (Salt)    (Water)

Q.15. Give two important uses of washing soda and baking soda.

Ans :- 

Uses of washing soda.Uses of baking soda
(i) Washing soda is used in glass, soap and paper paper industries.(i) For making baking powder, which is a mixture of baking soda and a mild edible acid such as tartaric acid.
(ii) It is used for removing permanent hardness of water.(ii) It is used in soda-acid fire extinguishers.

See Next Page No Below…

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