Chapter 2 : Acid , Bases and Salts

Class 10 Chapter 2 : Acid , Bases and Salts Internal Questions and Answers :

Internal Questions :

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 :  To identify the contents of each test tube using red litmus paper:

Immerse the litmus paper in the first test tube. If it remains red, it is distilled water.

Immerse the litmus paper in the second test tube. If it turns blue, it is a basic solution.

Immerse the litmus paper in the third test tube. If it remains red, it is an acidic solution.

Internal Questions :

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

Answer : : Curd and sour substances should not be kept in brass and copper vessels because they contain acids that can react with the metal, leading to the formation of harmful compounds that can be toxic if consumed.

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 : Hydrogen gas is usually liberated when an acid reacts with a metal. For example, when hydrochloric acid reacts with zinc, it produces zinc chloride and hydrogen gas. The presence of hydrogen gas can be tested by bringing a lit splint near the mouth of the test tube, where it will produce a 'pop' 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 : Metal compound A (calcium, ) reacts with dilute hydrochloric acid to produce effervescence () and hydrogen gas ()

      

Internal Questions :

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

Answer : Answer: , , etc., show acidic character in aqueous solutions because they ionize completely, releasing hydrogen ions ( ). Alcohol and glucose, being covalent compounds, do not ionize in water and therefore do not exhibit acidic character.

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

Answer : An aqueous solution of an acid conducts electricity because acids ionize in water, producing positively charged hydrogen ions ( ) and negatively charged ions. These ions allow for the flow of electric current through the solution.

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

Answer : Dry HCl gas does not change the color of dry litmus paper because litmus paper requires the presence of water (moisture) to exhibit a color change. In the absence of water, the dry litmus paper remains unaffected by dry HCl gas.

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

Answer : When diluting an acid, it is recommended to add the acid to water slowly because the reaction is exothermic. Adding water to concentrated acid can cause burns and splash out .

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

Answer : The concentration of hydronium ions ( ) decreases when a solution of an acid is diluted. Dilution reduces the number of acid particles per unit volume, resulting in a lower concentration of hydronium ions in the solution .

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

Answer : The concentration of hydroxide ions () increases when excess base is dissolved in a solution of sodium hydroxide. The additional base contributes more hydroxide ions, raising their concentration in the solution.

Internal Questions :

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 : The pH of solution A is 6 and pH of solution B is 8 . The solution A has more hydrogen ion concentration . The solution A is acidic and solution B is basic .

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

Answer : The concentration of (aq) ions determines the acidity of the solution. Higher concentrations of ions make the solution more acidic, while lower concentrations result in a less acidic or basic solution.

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

Answer : Yes, even basic solutions contain a small concentration of (aq) ions. However, their concentration is significantly lower compared to acidic solutions. Basic solutions are characterized by a higher concentration of ions, which make the solution alkaline or basic in nature.

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 : A farmer would typically treat the soil with quicklime (calcium oxide), slaked lime (calcium hydroxide), or chalk (calcium carbonate) in acidic soil conditions. These substances help neutralize the acidity and raise the level of the soil, making it more suitable for cultivation.

Internal Questions :

1. What is the common name of the compound ?

Answer : Bleaching powder .

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

Answer : Dry Slake lime .

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

Answer : Crystal sodium carbonate (Washing Soda) .

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

Answer :  When Sodium hydrogen carbonate is heated , then produced Sodium carbonate , water and carbon dioxide .

        .

5. Write an equation to show the reaction between Plaster of Paris and water.

Answer : The equation : 

 

(Plaster of Paris)      (Water)      (Gypsum)

Class 10 Chapter 2 : Acid , Bases and Salts Exercises :

1. A solution turns red litmus blue, its pH is likely to be
(a) 1       (b)     4       (c)   5        (d) 10

Answer :  (d) 10  .

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  .

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 .

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 .

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) When dilute sulphuric acid reacts with zinc granules.   

    

(b) When dilute hydrochloric acid reacts with magnesium ribbon.

      
(c) When dilute sulphuric acid reacts with aluminium powder.

    
(d) When dilute hydrochloric acid reacts with iron filings.
    

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

Answer : To demonstrate that compounds like alcohols and glucose do not exhibit acidic properties, you can perform an activity called "Comparison of Conductivity." Set up a circuit with a battery, a bulb, and two electrodes. Test the conductivity of an alcohol or glucose solution and compare it with an acidic solution like lemon juice. The acidic solution will conduct electricity, completing the circuit and lighting up the bulb, while the alcohol or glucose solution will not conduct electricity and keep the bulb off, indicating their non-acidic nature.

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

Answer : Distilled water does not conduct electricity because it lacks ions or impurities that can carry electrical charge. Rainwater, however, contains dissolved gases and impurities, which ionize and enable the conduction of electricity.

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

Answer : Acids require water to exhibit acidic behavior because they ionize in aqueous solutions, releasing hydrogen ions ( ). In the absence of water, acids cannot dissociate into ions and, therefore, do not display their characteristic acidic properties.

9. Five solutions A,B,C,D and E when tested with universal indicator showed 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 in increasing order of hydrogen-ion concentration.

Answer :  Here , the of solution A = 4  ; the of solution B = 1 ; the of solution C = 11  ;  the of solution D = 7 and the of solution E = 9

(a) The solution D is neutral .

(b) The solution C is strongly alkaline .

(c) The solution B is strongly acidic .

(d) The solution A is weakly acidic .

(e) The solution E is weakly alkaline .

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 (  ) is added to test tube B. In which test tube will the fizzing occur more vigorously and why?

Answer : The fizzing will occur more vigorously in test tube A, where hydrochloric acid ( ) is added to the magnesium ribbon. This is because  is a stronger acid compared to acetic acid ( ). Strong acids, like , ionize completely in water, producing a higher concentration of hydrogen ions ( ) . The higher concentration of  ions leads to a more vigorous reaction with magnesium, resulting in increased fizzing.

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

Answer : As milk turns into curd, the will decrease. This is because the fermentation process converts lactose (milk sugar) into lactic acid, which is an acid. The increased concentration of lactic acid lowers the pH of the curd.

12. A milkman adds a very small amount of baking soda to fresh milk.
(a) Why does he shift the of the fresh milk from 6 to slightly alkaline?
(b) Why does this milk take a long time to set as curd?

Answer :  (a) The milkman adds baking soda (sodium bicarbonate) to fresh milk to shift its from 6 to slightly alkaline. Baking soda is a basic compound that raises the pH by neutralizing any acidic components present in the milk.

(b) The addition of baking soda to fresh milk increases its alkalinity, which inhibits the activity of the bacteria responsible for curdling. As a result, the milk takes a longer time to set as curd.
13. Plaster of Paris should be stored in a moisture-proof container. Explain why?

Answer :  Plaster of Paris is a white powder and on mixing with water, it changes to gypsum once again giving a hard solid mass.

 

So, Plaster of Paris should be stored in a moisture-proof container .

14. What is a neutralisation reaction? Give two examples.

Answer : The reaction between an acid and a base to give a salt and water is called a neutralisation reaction .

Example : 

(i) 

(ii) 

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

Answer :  Use of washing soda are :

(i) It is used for removing permanant hardness of water .

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

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

Use of baking soda are :

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

(ii) It is used for making baking powder .

(iii) It is also an ingredient in antacids .