Acid Bases and Salts 

CBSE extra question 

class 10



TWO MARKS QUESTIONS

1. Two solutions ‘A’and ‘B’have pH value 3.0 and 10.5 respectively. Which of these will turn
a. Blue litmus solution to red,
b. Phenolphthalein from colourless to pink? Justify your answer in each case.

a. ‘A’with pH = 3, will turn blue litmus red because

The red litmus will turn blue in Na CO solution. 

2. What is the colour of litmus in a solution of ammonium hydroxide?
Red litmus will turn blue green colour in a solution of ammonium hydroxide.

3. On adding dilute hydrochloric acid to copper oxide powder, the solution formed is blue green. Predict the new compound formed which imparts a blue green colour to the solution.
 Copper chloride imparts blue green colour to the solution.

4. How does flow of acid rain water into river makes the survival of aquatic life in the river difficult?
Acidic water makes aquatic species uncomfortable.
Aquatic species are more comfortable in the pH 7 to 7.8.

5. The pH of soil ‘A’is 7.5, while that of soil “B is 4.5. Which of the two soils A or B should be       treated with powdered chalk to adjust the pH and why?
Soil ‘B’is acidic, therefore it needs to be treated with powdered chalk to adjust its pH because chalk is basic, which will make soil neutral.

6. Oxides of metals are basic while those of non-metals are acidic. Explain.
Metal oxides dissolve in water to form base basic in nature. On the other hand non metals dissolve in water to form acids, acidic in nature  
7.Arrange the following in an increasing order of their pH values: NaOH solution, Blood, Lemon juice.
Lemon juice < Blood < NaOH solution.

8. What is the difference between slaked lime and lime water?
  The solid Ca(OH) is slaked lime whereas clear solution of Ca(OH) in water is lime water.

9. During summer season, a milkman usually adds a very small amount of baking soda to fresh milk. Give one reason.
Baking soda is basic in nature, it will not allow milk to turn sour due to the formation of lactic acid.

10. Curd is not kept in copper and brass utensils, why?
Curd contains lactic acid which can make poisonous
compounds with brass and copper vessels.

11. Fresh milk has pH = 6. When it changes to curd will its pH value increase or decrease?
 pH value will decrease when milk changes to curd.

12. At what pH in the mouth is tooth decay faster and why?
 At pH lower than 5.5, tooth decay becomes faster
because calcium phosphate (enamel) reacts with acid and gets corroded.

13. How does the pH change when solution of a base is diluted?
When solution of a base is diluted, its pH decreases


14. Dry HCl gas does not change the colour of dry blue litmus. Give reason to justify it.
 Dry HCl (g) does not form ions, therefore it does not affect dry blue litmus.

15. What are olfactory indicators?
Those indicators whose smell changes in acidic and basic solutions.



16. A white chemical compound becomes hard on mixing proper quantity of water. It is also used to maintain joints in fixed position. Name the chemical compound and write its chemical formula. Write the chemical equation to show what happens when water is added to this compound in proper quantity.
 [CBSE Sample Paper 2018, CBSE 2016]

 CaSO4. 2 H2O is the formula of the compound. The
name of compound is ‘Plaster of Paris’ (Calcium sulphate hemihydrate).
CaSO 4 $ 2 H 2 O + 2 H 2 O $CaSO4 $ 2H 2 O
(Plaster of Paris ) (Gypsum)


17. Write the chemical equation to describe how baking soda is produced on a large scale. Also write the chemical name of the products formed in the reaction.   [CBSE 2016]    
 NH 3 + H 2 O + CO 2 + NaCl $NaHCO 3 + NH 4 Cl
(Sodium hydrogen (Ammonium carbonate) chloride )



18. 15 mL of water and 10 mL of sulphuric acid are to be mixed in a beaker
  a.      State the method that should be followed with reason.
  b.  What is this process called?
Ans : [CBSE 2015]
a. Acid should be added to the water slowly with
constant cooling because the reaction is highly exothermic.
b. This process is called dilution.


19. Name the acid present in the following: 
      a. Tomato,
b. Vinegar, 
c. Tamarind
Ans :
a.        Tomato contains oxalic acid.
b.          Vinegar contains acetic acid. 
c. Tamarind contains tartaric acid.

20. You have two solutions A and B. The pH of solution ‘A’is 6 and the pH of solution ‘B’is 8. Which solution has more hydrogen ion concentration? Which one of this is acidic and which one is basic?    [CBSE 2016]
Ans :
‘A’has more H ion concentration.
‘A’is acidic while ‘B’is basic.



21. Give suitable reasons to justify the following statement: An aqueous solution of sodium chloride is neutral but an aqueous solution of sodium metal is basic.
Ans :
Sodium chloride is made up of a strong base, NaOH and a strong acid, HCl. Therefore, its aqueous solution is neutral in nature.
Sodium metal reacts with water to form NaOH(Base)
22. What is the action of litmus on
a         dry ammonia gas
b       solution of ammonia gas in water?
Ans : [CBSE 2016]
 a. There is no effect of dry litmus on dry ammonia gas.
b. Solution of ammonia will turn red litmus blue.

23. State what does pH of solution signify? Three solutions A, B and C have pH values of 6, 2 and 10 respectively. Which one of these solutions is highly acidic? Which solution will turn red litmus blue?
Ans : [CBSE 2015]
pH of solution signifies the nature of the solution i.e., it is weakly acidic, strongly 1 acidic, neutral, weakly basic, strongly basic.
‘B’with pH = 2 is strongly acidic.
‘C’with pH = 10 will turn red litmus blue.



24. Define an acid and a base. Name one weak acid and one strong acid.
Ans : [CBSE 2015]
Acid is a substance which gives H ions in an aqueous solution.
Base is substance which gives OH ions in the aqueous solution.
CH3COOH is a weak acid, H2SO4 is a strong acid.


  25. What is universal indicator? State the purpose for
which this indicator is used.
Ans : [CBSE 2015]
 Universal indicator is a mixture of a number of indicators. It is used to determine pH of a solution.

26. Name the natural source of each of the following acid:
a       Citric acid,
b     Oxalic acid,
c        Lactic acid,
d        Tartaric acid.
Ans : [CBSE 2014]
 a Citric acid—Lemon, Orange.
b         Oxalic acid—Tomato, Guava
c       Lactic acid—Curd, Sour milk
d    Tartaric acid—Tamarind




27. A student detected the pH of four unknown solutions A, B, C and D as follows: 11, 5, 7 and 2. Predict the nature of these solutions.
pH = 11 is basic
pH = 5 is acidic
pH = 7 is neutral
pH = 2 is strongly acidic

28.    Give two uses of baking soda and washing soda each.  [CBSE 2013]
Ans :
Use of baking soda:
a. It is used in making of bread, biscuits, cakes
b. It is used as an antacid.
Use of washing soda:
a. It is used as a cleansing agent.
b. It is used to remove hardness of water.

29. What is colour of FeSO .7H O crystals? How does this colour change upon heating? Give a balanced chemical equation for the change.
 [CBSE 2011]
Ans :
 FeSO4.7H O is pale green in colour. It becomes dirty
white on heating.
FeSO4.7H O $FeSO4 + 7H O
If it is heated strongly Fe2O3 and SO2 , SO3 gases will be formed .


 30. What are olfactory indicators? Dry HCl gas does not change the colour of dry blue litmus. Give reason.

 [CBSE 2011]
Ans :
Olfactory indicators: They give different smell in acids
and bases.
Dry HCl(g) does not form ions, so there is no effect on litmus.


31. Classify the following salts into acidic, basic and neutral salts: Potassium sulphate, ammonium chloride, sodium carbonate, sodium chloride

[CBSE 2011]
Ans :
       Acidic:  Ammonium chloride,
       Basic:    Sodium carbonate,
       Neutral: Potassium sulphate, sodium chloride.