CBSE Class 10 Chapter 2 Acids, Bases and Salts Exercise Questions Answer

 CBSE Class 10 Chapter 2 Acids, Bases and Salts  Exercise Questions Answer 

Q1	A solution turns red litmus blue, its pH is likely to be
	(a) 1                     (b) 4                    (c) 5                        (d) 10
Ans.	(d) 10 Explanation: Because litmus paper turns blue when the solution pH value more than 7.

 

Q2	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
Ans.	(c) HCl Explanation: Eggshells have calcium carbonate. When we mix them with hydrochloric acid, they give off carbon dioxide (CO2). If we pass this gas through lime water, it makes the lime water look milky.

 

Q3	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
Ans.	(d) 16 mL Explanation: If 10 ml of NaOH requires 8 ml of HCl, then 20 ml of NaOH will require 16 ml of HCl because it's double the amount.

 

Q4	Which one of the following types of medicines is used for treating indigestion?
	(a) Antibiotic (b) Analgesic (c) Antacid (d) Antiseptic
Ans.	(c) Antacid Explanation: Indigestion occurs due to overproduction of stomach acid. Medicine used to treat this situation called antacids.

 

Q5

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.

Ans.

(a) Word equation: Dilute sulphuric acid + zinc → Zinc Sulphate + Hydrogen Gas Balanced equation: H2SO4(aq) + Zn → ZnSO4(aq) + H2(g) (b) Word equation: Dilute Hydrochloric + Magnesium → Magnesium Chloride + Hydrogen Gas Balanced equation: 2HCl(aq) + Mg → MgCl2(aq) + H2(g) (c) Word equation: Dilute Sulphuric Acid + Aluminium → Aluminium Sulphate + Hydrogen Gas Balanced equation: 3H2SO4(aq) + 2Al(s) → Al2(SO4)3(aq) + 3H2(g) (d) Word equation: Dilute Hydrochloric Acid + Iron → Ferrous Chloride + Hydrogen Gas Balanced equation: 6HCl(aq) + 3Fe(s) → 3FeCl2(aq) + 3H2(g)

 

Q6	Compounds such as alcohols and glucose also contain hydrogen but are not categorised as acids. Describe an Activity to prove it.
Ans.	Insert two nails into a wooden or rubber cork. Place the cork with the nails in a beaker as shown in the diagram. Connect one of the nails to a light bulb, a 6-volt battery and a wire that is linked to a switch. Pour alcohol or glucose into the beaker until the nails are immersed in the liquid. Turn the switch on to complete the circuit and we will observe that the bulb does not light up, despite the electrical connection. Empty the beaker, removing the alcohol or glucose. Add hydrochloric acid (HCl) solution to the beaker, covering the nails. Turn the switch on again and this time, we will observe that the bulb glows brightly. This experiment demonstrates that the flow of electricity is possible through the HCl solution, indicating that acids can conduct electricity. Conversely, when alcohol or glucose was used, the bulb did not light up, indicatting that these substances do not conduct electricity.

 

Q7	Why does distilled water not conduct electricity, whereas rain water does?
Ans.	Distilled water does not conduct electricity because it is extremely pure and lacks dissolved ions. In other side, rainwater contains a small amount of dissolved ions like- carbon dioxide from air that form carbonic acid, This means that it has hydrogen ions and carbonate ions, which enables it to conduct electricity.

 

Q8

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

Ans.

Acids do not show their acidic behavior in the absence of water because the fundamental process that defines acid behavior is the dissociation or ionization of hydrogen ions (H+) in water. This process is essential for acids to act as acids. In the absence of water, the hydrogen ions (H+) remain tightly bound within the acid molecules and there are no free hydrogen ions available to display acidic properties.

 

Q9

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: A neutral solution has a pH of 7. Solution D has a pH of 7, so it is neutral. (b) Strongly Alkaline: A strongly alkaline solution has a pH greater than 7. Solution C has a pH of 11, so it is strongly alkaline. (c) Strongly Acidic: A strongly acidic solution has a pH less than 7. Solution B has a pH of 1, so it is strongly acidic. (d) Weakly Acidic: A weakly acidic solution has a pH between 7 and 4. Solution A has a pH of 4, so it is weakly acidic. (e) Weakly Alkaline: A weakly alkaline solution has a pH between 7 and 9. Solution E has a pH of 9, so it is weakly alkaline. In increasing order of hydrogen ion concentration, pH 11(C) < pH 9(E) < pH 7 (D) <  pH 4 (A) < pH 1 (B)

 

Q10

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 (CH3COOH) 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?

Ans.

The fizzing or the effervescence, in this case, will occur more vigorously in test tube A, where hydrochloric acid (HCl) is added compared to test tube B with acetic acid (CH3COOH) because Hydrochloric acid (HCl) is a strong acid, while acetic acid (CH3COOH) is a weak acid. The difference in their reactivity with magnesium is due to their ability to donate hydrogen ions (H+). Following reaction are take place: 2HCl + Mg → MgCl2 + H2  -------- vigorous fizzing 2CH3COOH + Mg → Mg(CH3COO)2 + H2 ---------------Slow fizzing

 

Q11	Fresh milk has a pH of 6. How do you think the pH will change as it turns into curd? Explain your answer.
Ans.	When milk turns into curd, its pH decreases because the lactic acid bacteria in the curd-forming process produce lactic acid by lactic acid bacteria. So, the concentration of hydrogen ions (H+) in the milk increases, causing the pH to decrease. It is indicate that the milk becomes more acidic as it turns into curd. Lactose (in milk) → Lactic Acid

 

Q12	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?
Ans.	(a) The milkman shifts the pH of the fresh milk from 6 to slightly alkaline to prevent the milk from souring due to lactic acid production. (b) This milk take a long time to set as curd because this alkaline pH can lead to a longer time for the curd to set due to the slower activity of the bacteria in this environment.

 

Q13	Plaster of Paris should be stored in a moisture-proof container. Explain why?
Ans.	Plaster of Paris should be stored in a moisture-proof container because When it comes into contact with water, it converts in its original form gypsum and become useless. CaSO4.½H2O + 1½H2O → CaSO4·2H2O

 

Q14	What is a neutralisation reaction? Give two examples.
Ans.	A neutralization reaction is a chemical reaction between an acid and a base that results in the formation of water and a salt. In this reaction, the acidic properties of the acid and the basic properties of the base are neutralized. Acid + Base → Salt + Water Examples: HCl + NaOH → NaCl + H2O H2SO4 + Ca(OH)2 → CaSO4 + 2H2O H2CO3 + Mg(OH)2 → MgCO3 + 2H2O

 

Q15	Give two important uses of washing soda and baking soda.
Ans.	Washing Soda Baking Soda 1. Cleaning agent for various surfaces and fabrics. 1. It acts as a leavening agent in baking. 2. Water softener to reduce water hardness. 2. It can be used to neutralize odors in refrigerators, shoes, carpets and other household items.