This document contains 17 questions and answers about acids, bases and salts. Some key points covered include: - Milk has a pH of 6, which decreases when it turns to curd due to lactic acid production. - Solutions with pH values of 4, 7, 9, 11 and 1 are identified as weakly acidic, neutral, weakly alkaline, strongly alkaline and strongly acidic respectively. - Toothpastes neutralize excess acid in the mouth and prevent tooth decay. - Heating copper sulfate changes its color from blue to white as it loses water of crystallization.

1. Class10
ACIDS , BASES , SALTS
IMPORTANT QUESTIONS AND
ANSWERS

2. 1.Fresh milk has a pH of 6. When it changes into curd (yogurt), will
its pH value increases or decreases? Why?
Ans:
When milk change into curd, its pH will decrease. Because curd
contains lactic acid, so H+ ion concentration increases and thus pH
will decrease.
2. 11 and 9 respectively when tested with universal indicator. Which
solution is:
i) Neutral ii) Strongly alkaline iii) Strongly alkaline iv) Weakly
acidic and v) Weakly alkaline.
Arrange the pH in increasing order of hydrogen ion concentration.
Ans:
(i) B 7 (ii) D 11 (iii) C 1 (iv) A 4 (v) E 9
Arrangement: D,E,B,A,C or 11,9,7,4,1.

3. 3.Sweet tooth may lead to tooth decay. Explain why? What is the
role of tooth paste in preventing cavities?
Ans:
Sweet tooth leads to tooth decay, which is caused by the action
of bacteria on food particles remaining in the mouth and acid
is formed. As a result, the pH of the mouth falls below 5.5 and
the tooth enamel dissolves resulting in cavities. Toothpastes
are generally basic, they neutralize the excess acid produced in
the mouth and prevent tooth decay.

4. 4.A metal is treated with dilute sulphuric acid. The gas evolved
is collected by the method shown in the figure:
(i) Name the gas (ii) Is the gas soluble or
(ii) insoluble in water? (iii) Is the gas lighter or
Heavier than air? (iv) How will you test the gas?
(v) If the metal used above is zinc then write the chemical
equation for the evolution of gas.
(vi) Write one industrial use of the gas evolved.
Ans:
(i)Hydrogen gas (ii) Is soluble in water (iii) It is lighter than air
(iv) Test for H2 Gas: Bring a burning matchstick near the gas jar.
It burns with a pop sound.
(v) Zn(s) + H2SO4(dil) ZnSO4(aq) + H2(g)
(vi) Liquid hydrogen is used as a fuel in rockets.

5. 5.A few crystal of copper sulphate are heated in dry boiling tube:
(i) What is the colour before and after heating?
(ii) What is the reason for the colour change?
(iii) Can its original colour be restored? How?
Ans:
(i) Blue and white respectively.
(ii) Water of crystallization is lost on heating.
(iii) Yes, by adding water.

6. 6.(a) Rahul has been stung by a honey bee and is in great pain. (i)
what could be the reason for this burning pain? (ii) State the
type of chemical compound that can be applied on the
affected area to give relief to Rahul.
(b) Write the name and formula of each of the following:
i) An acidic salt
ii) A basic salt
iii) A neutral salt.
Ans:
(a) i) Bee – sting injects methanoic acid.
ii) A mild base like baking soda will give relief.
(b) i) Ammonium chloride, NH4Cl
ii) Sodium carbonate, Na2CO3
iii) Sodium chloride, NaCl.

7. 7.(a)In a tabular form, write the colours of the following indicators in presence of
acid and bases: Litmus solution, Phenolphthalein solution, methyl orange
solution.
b) Classify the following given solutions A and B into acidic and basic,giving
reason.
Solution A: [H+] (<) [OH]-
Solution B: [H+] (>) [OH]-
Ans:
(a)
(b) Solution A: Basic solution
Because,[H+] is lesser than 1.0 x 10-7
Solution B: Acidic solution
Because,[H+] is greater than 1.0 x 10-7 m
Indicators Acid Base
Litmus solution Blue to Red Red to Blue
Phenolphthalein Colourless Pink
Methyl orange Yellow Pink

8. 8. (i) A local magician was showing magic in a village street. He took egg shell and
poured a solution over it. As a result, effervescence were formed. When he took a
burning matchstick over it, it went off:
(a) Identify the solution poured and the substance present in egg shell.
(b) What is the reason behind effervescence?
(c) Write its balanced chemical equation.
(d) Give the common name of the substance present in the egg shell.
(ii) Draw a labelled diagram to show that acid solution in water conducts electricity.
Ans:
(i) a) Solution is an acid. Substance in egg shell is calcium carbonate.
b) Effervescence is due to the evolution of CO2 gas.
c) 2HNO3 + CaCO3 2Ca(NO3)2 + H2O + CO2
d) Lime stone.
ii) 6 Volt battery

9. 9.(i) Name the gas which is liberated when an acid reacts with a metal.
How will you test the presence of this gas?
(ii) Write the chemical equation for the reaction of zinc metal with:
(a) Hydrochloric acid and (b) With sodium hydroxide. Write the
chemical name of salt obtained in each case.
iii) Identify the acid and base for ammonium chloride salt. What would be
the nature of this salt? Mention the pH range of this salt.
Ans:
i) Hydrogen gas. It burns with pop sound.
ii) (a) Zn(s) + 2HCl(aq) ZnCl(aq) + H2(g)
Zinc chloride
b) Zn(s) + 2NaoH (aq) Na2ZnO2(aq) + H2(g)
Sodium Zincate
iii) HCl, NH4OH NH4OH + HCl NH4Cl + H2O
Nature of salt – acidic as it is formed by neutralization of strong acid and
weak base.
Its pH value will be less than 7 (pH range 1-6)

10. 10.(a) Five solution A,B,C,D and E when tested with universal indicator
showed pH as 4,1,11,7 and 9 respectively. Which solution is:
(i) Neutral (ii) Strongly alkaline (iii) Strongly acidic (iv) Weakly
acidic (v) Weakly alkaline?
Arrange the solutions in increasing order Of H+ ion concentration.
b) Name the acid and base from which the following salts have been formed.
(i) Sodium accetate.
Ans.
a) i) solution d ii) solution c iii) solution B iv) solution A v)
solution E
Increasing order C,E,D,A,B
b) i) Acid - CH3COOH (Acetic acid)
Base - NaOH (Sodium hydroxide)
ii) Acid - HCl (Hydrochloric acid)
Base - NH4OH (Ammonium hydroxide)

11. 11.Write balanced chemical equations only for the following
chemical properties of acids:
(a) When an acid reacts with a metal.
(b) When an acid reacts with a metal bicarbonate.
(c) When an acid reacts with a base.
ii) Three solution A,B and C has pH values 5,8 and 10
respectively. Amongst the three, which solution has
maximum hydrogen ion concentration? Classify the nature of
the three solutions as acidic or basic.
Ans:
i) a) Zn + H2SO4 ZnSO4 + H2
b) HCl + NaHCO3 NacL + H2O + CO2
C) HCl + NaoH NaCl + H2O
ii) A has maximum [H+] concentration A is acidic B and C are
basic in nature.

12. 12.What is meant by water of crystallization ? How many
molecules of water are present in hydrated copper sulphate?
Write its formula. What colour change do you observe when it
is heated?
Ans:
Water of crystallization is the fixed number of water molecules
present in one formula unit of salt.
i) Five molecules of water.
ii) Formula: CuSO4 5H2O
iii) When heated its colour changes from blue to white.

13. 13.Write the chemical formula of bleaching powder. Write
balanced chemical equation involved in the preparation of
bleaching powder and write its three uses.
Ans:
Chemical formula : CaOCl2
Chemical equation:
Ca(OH)2 + Cl2 CaOCl2 + H2O
Uses:
i) For bleaching cotton and linen in textile industry
ii) As an oxidizing agent in a chemical industry.
iii) For disinfecting water.

14. 14.Sodium hydrogen carbonate is a basic salt. Justify the
statement. How is it converted into washing soda? Explain
Ans:
It is a salt produced by the neutralization reaction between a
strong base (NaOH) and a weak acid (H2CO3) hence it is a
basic salt.
It is heated strongly to produced sodium carbonate.
2NaHCO Na2CO3 + H2O + CO2
Sodium carbonate is recrystallized to produce washing soda.
Na2CO3 + 10H2O Na2CO3.10H2O

15. 15.i) Write the chemical formula of each of the following:
a) Plaster of pairs b) Gypsum
ii) How can plaster of pairs be converted into gypsum?
iii) List any one use of plaster of pairs.
Ans:
i) CaSO4.½H2O B) CaSO4.2H2O
ii) By mixing with water
CaSO4.½H2O + 1½ H2O CaSO4.2H2O
iii) For making toys, for supporting fractured bones.

16. 16.Name the three products of ‘chlor – alkali’ process. Write one
commercially or industrially important material each that can
be prepared from each of these products.
ANS:
The three products are:
Sodium hydroxide (NaOH) chlorine (Cl2) and hydrogen(H2).
NaOH - for soaps and detergents and paper making or artificial
fibers.
Cl2 – PVC, pesticides, CFCs.
H2 – fuels, margarine, NH3 for fertilizers.

17. 17.a) For the preparation of cakes, baking powder is used. If at
home your mother uses baking soda instead of baking powder,
how will it affect the taste of the cake and why?
b) How is baking soda be converted into baking powder?
c) What makes the cake soft and spongy?
Ans;
a) The cake will have a bitter taste because of the formation of
Na2CO3/sodium carbonate while baking/heating.
b) By adding tartaric acid.
c) The liberated Co2 gas.