This chapter is from Module 2 Matter in Our Surroundings Class 10 Science and Technology (212). This post provides you complete answer of all intext and terminal questions with a complete explanation with diagrams.
Our experienced teachers have provided
easy and accurate answers to all questions that will help you complete your
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Acids, Bases and Salts Questions- Answers
In this lesson form NIOS class 10 Science, students will
gain the knowledge about chemical bond and types, properties of ionic
compounds, properties of covalent compounds.
Intext Questions 8.1 with Answers
Q1. Put the following substances in acid or base bottle.
(a) Milk of magnesia
(b) Gastric juice in humans
(c) Soft drinks
(d) Lime
water
(e) Vinegar
(f) Soap
Answer
Acidic – (b) Gastric juice in humans (c)
soft drinks (e) vinegar
Basic – (a) milk of magnesia (d) lime
water (f) soap
Q2. What will happen if you add a drop of the following on a cut unripe apple, curd, caustic soda solution and soap solution
(i) Phenolphthalein
(ii) Litmus
Answer
(i) Phenolphthalein
It remains colourless in cut unripe and curd (acidic substances)
It turns pink in caustic soda and soap solutions (basic substances)
(ii) Litmus
Blue litmus turns red in cut unripe apple and curd (acidic substances)
Red litmus turns blue in caustic soda and soap solution (basic
substances)
Intext Questions 8.2 with Answers
Q1. Name the substances in which the following acids are present:
(a) Ethanoic acid (b) Tartaric acid
Answer
(a)
Ethanoic
acid – Vinegar
(b)
Tartaric
acid - Tamarind
Q2. Which of
these acids would be partially dissociated in their aqueous solution?
(a) HBr
(b) HCN
(c) HNO3
(d) C2H5COOH
Answer
(a) HCN
and C2H5COOH are weak acids so these partially dissociate
in aqueous solution.
Q3. An acid
reacts with substance ‘X’ with liberation of a gas which burns with a ‘pop’
sound when a burning match stick is brought near it. What is the nature of ‘X’?
Answer
The substance ‘X’s is a metal.
Q4. An acid
reacts with a substance ‘Z’ with liberation of CO2 gas. What can be
the nature of ‘Z’?
Answer
The substance ‘Z’ can be a metal carbonate
or metal hydrogen carbonate
Na2CO3 + 2HCl →2NaCl + H2O
+CO2
NaHCO3 + HCl → NaCl + H2O
+CO2
Q5. Which of the following oxides will react with a base?
(a) CaO
(b) SO2
Answer
SO2 is a non-metal oxide and
non-metal oxides react with bases to form salt and water.
Intext Questions 8.3 with Answers
Q1. Why does the colour of dry blue litmus paper remain unchanged even when it is brought in contact with HCl gas?
Answer
The colour of dry blue litmus paper
remains unchanged in contact with dry HCl gas because dry HCl gas does not
produce H+ ions.
Acids show acidic nature only in the presence of water. When HCl dissolves in water, it forms H+ ions which turns blue litmus red.
Q2. How does water help in dissociation of acids and bases?
Answer
Water helps in the dissociation of acids
and bases by weakening the forces or chemical bond holding the ions together,
due to which free ions are formed in solution.
Acids dissociate in water to give H+ ions
Bases dissociate in water to give OH-
ions.
Only in aqueous solution do acids and bases show their acidic and basic properties.
Q3. Identify the nature of the following aqueous solutions (whether acidic, basic or neutral)
(a) Solution A: [H+] < [OH-]
(b) Solution B: [H+]> [OH-]
(c) Solution C: [H+] = [OH-]
Answer
(a) Solution A: [H+] < [OH-] – Basic in nature
(b) Solution B: [H+]> [OH-] – Acidic in nature
(c) Solution C: [H+] = [OH-] – Neutral
Intext Questions 8.4 with Answers
Q1. POH of a solution is 5.2. what its pH? comment on the nature (acidic, basic or neutral) of this solution.
Answer
We know that
pH + pOH=14
pH= 14- pOH
pH= 14 - 5.2
pH= 8.8
Since pH is higher then 7 , so the solution is basic in nature.
Q2. PH of a solution is 9. What is the concentration of H+ ion in it.
Answer
pH=9
we know pH= -log[H+]
therefore
[H+] =10-pH
[H+] =10-9
[H+] = 1.0 ×10-9 mol L-1
Q3. What is the nature(whether acidic, basic or neutral) of the following solutions?
(a) Solution A: pH = POH
(b) Solution B: pH > POH
(c) Solution C: pH < POH
Answer
(a) Solution A is neutral
(b) Solution B is basic.
(c) Solution C is acidic
Intext Questions 8.5 with Answers
Q1. Identify
acid radical and basic radical in CaSO4.
Answer
Acid radial – SO42-
Basic radical – Ca2+
Q2. CuSO4
was prepared by reacting an acid and a base. Identify the acid and the base
that must have been used in this reaction.
Answer
Copper sulphate can be prepared by H2SO4
and Cu(OH)2
Cu(OH)2 + H2SO4 → CuSO4 + 2H2O
Q3. Which one
of the following is the correct formula of Plaster of Paris?
CaSO4.H2O or 2CaSO4.H2O
Answer
CaSO4.H2O
Terminal Exercise Questions with Answers
A. Objective Types Questions
I. Mark the correct choice
1. Lemon juice contains
(a) Tartaric acid
(b) Ascorbic acid
(c) Acetic acid
(d) Lactic acid
Correct answer- (a) Ascorbic acid
2. Aqueous solution of acids conducts electricity. This shows that
(a) They contain H+ ions
(b) They contain OH- ion
(c) They contain cations and anions
(d) They contain both H+ and OH- ions
Correct answer - (c) They contain cations and anions
3. Which of the following is not a strong acid?
(a) HCl
(b) HBr
(c) HI
(d) HF
Correct answer- (d) HF
4. Self-dissociation of water produces
(a) A large number of H+ ions
(b) A large number of OH- ions
(c) H+ and OH- ions in equal numbers
(d) H+ and OH- ions in unequal numbers
Correct answer- (c)
H+ and OH- ions in equal numbers
5. In any aqueous basic solution
(a) [H+] > [OH-]
(b) [H+] < [OH-]
(c) [H+] = [OH-]
(d) [H+] = 0
Correct answer - (b) [H+] < [OH-]
6. In aqueous solution of HCl which of the following species is not present?
(a) H+
(b) OH-
(c) HCl
(d) Cl-
Correct answer - (b) OH-
7. Which of the following is not a raw material for manufacturing washing soda?
(a) Lime stone
(b) Ammonia
(c) Slaked lime
(d) Sodium chloride
Correct answer - (c) Slaked lime
II. Mark the following statements as true(T) of false (F):
1. Acids furnish H+ ions only in the presence of water.
2. Lime water turns blue litmus red.
3. HF is a strong acid.
4. H2 gas is produced when acids react with metal oxides.
5. Corrosive action of acids is due to H+ ions present in them.
6. When pH of the rain water become more than 5.6. it is called acid rain.
7. Aqueous solutions of all the salts are neutral i.e. neither acidic nor basic in nature.
Answer
1. Acids
furnish H+ ions only in the presence of water. (T)
2.Lime
water turns blue litmus red.(F)
3.HF
is a strong acid. (F)
4.`H_2` gas is produced when acids react with metal oxides. (F)
5. Corrosive
action of acids is due to H+ ions present in them. (T)
6. When
pH of the rain water become more than 5.6. it is called acid rain. (F)
7. Aqueous solutions of all the salts are neutral i.e. neither acidic nor basic in nature.(F)
III. Fill in the blanks:
1.
Acids taste ……………………while bases taste……….
2.
Milk of magnesia turns………………. litmus……….
3.
One mole of sulphuric acid would furnish ……. mole/s of H+
ions and …………. mole of SO42- ions.
4.
………. gas is produced when acids react with metal hydrogen
carbonates.
5.
Lime water turns milky on passing CO2 gas due to the
formation of …………………
6.
The reaction between an acid and a base is known as ……………….
7.
Bee sting injects ………………acid which causes severe pain and
burning sensation.
8.
In NH4NO3 the acid radical is………….and the
basic radical is………………
9.
Chemically baking soda is………………………….
Answer
1. Acids
taste sour while bases taste bitter.
2. Milk
of magnesia turns red litmus blue.
3.One
mole of sulphuric acid would furnish 2 mole/s of H+ ions and 1 mole
of SO4 2- ions.
4. CO2
gas is produced when acids react
with metal hydrogen carbonates.
5. Lime
water turns milky on passing CO2 gas due to the formation of calcium
carbonate.
6. The
reaction between an acid and a base is known as neutralisation reaction.
7. Bee
sting injects methanoic acid which causes severe pain and burning
sensation.
8. In
NH4NO3 the acid radical is NO3-
and the basic radical is NH4+.
9.Chemically baking soda is sodium hydrogen carbonate.
B. Descriptive Questions
Q1. What is an
acid?
Answer
An acid is the substance that produce H+
ions in aqueous solution. They are sour in taste and turn blue litmus red.
Q2. Give two examples
of acids found in food articles.
Answer
Ascorbic acid – found in lemon and citrous
fruits.
Acetic acid – found in vinegar
Q3. What is a
base?
Answer
A base is the substance that produce OH-
ions in aqueous solution. They are bitter in taste and turn red litmus blue.
Q4. Give two
examples of bases.
Answer
Sodium hydroxide (NaOH)
Calcium hydroxide (Ca(OH)2)
Q5. What are
indicators?
Answer
Indicators are substances that show one
colour in acidic medium and another in basic medium. They are used to identify
whether a solution is acidic or basic. Examples - Litmus, phenolphthalein and
methyl orange.
Q6. What is
the colour of methyl oranges indicator in )i) acidic medium (ii) basic medium
Answer
In Acidic medium – Methyl orange gives a
red colour.
In Basic medium – Methyl orange gives a
yellow colour.
Q7. Why do
solution of acids and bases conduct electricity?
Answer
Solutions of acid and bases conduct
electricity because they dissociate in water and produce cations and anions.
These ions carry electric current through the solution.
Q8. Differentiate
between strong and weak acids and give one example of each.
Answer
|
Strong
acids |
Weak
acids |
|
They dissociate
completely in water. |
They dissociate
partially in water. |
|
They produce
large concentration of H+ ions. |
They produce a
relatively small concentration of H+ ions. |
|
Example- HCl |
Example- CH3COOH |
Q9. Write down
the reaction between zinc and sulphuric acid.
Answer
Zn + H2SO4 →ZnSO4 + H2
Q10.
Which gas is evolved when an acid reacts
with metal carbonates? Which other category of compound would produce the same
gas on reacting with acids?
Answer
When an acid reacts with a metal carbonate,
carbon di oxide gas is evolved.
Na2CO3 + 2HCl→ 2NaCl + H2O
+ CO2
The same gas is also produced when acid
reacts with metal hydrogen carbonates.
NaHCO3 + HCl→ NaCl + H2O
+ CO2
Q11. What type
of oxides react with acids? Give one example of this type of oxide and write
down the balanced equation for the reaction.
Answer
Metal oxides (basic oxides) react with
acids and form salt and water.
Example – Copper oxide
CuO + HCl → CuCl2 + H2O
Q12. What is
the name given to the reaction between an acid and a base? What are the
products formed in such reactions?
Answer
The reaction between an acid and a base is
called a neutralisation. Salt and water are formed in this reaction.
`NaOH+ HCl→ NaCl + H_2O`
Q13 “Corrosive
action of acids is not related to their strength”. Justify this statement.
Answer
The corrosive action of acid is due to the
presence of H+ ions and not due to their strength. An acid may be
strong or weak depending on the extent of its dissociation in water but both
strong and weak acids contain H+ ions and can show corrosive
properties.
Q14. Give one
example each of the following (i) a strong base (ii) a weak base
Answer
Strong base – Sodium hydroxide (NaOH)
Weak base – Ammonium hydroxide (NH4OH)
Q15. List
three categories of substances that can react with a base. Give one example of
each and write the chemical reaction involved in each case.
Answer
A base can react with the following three categories of substances:
(i) Acids
Example- Hydrochloric acid (HCl)
NaOH + HCl →NaCl + H2O
(ii) Non -metal oxides
Example – Carbon di oxide (CO2)
2NaOH + CO2 →Na2CO3 +H2O
(iii) Ammonium salts
Example – Ammonium chloride (NH4Cl)
NaOH + NH4Cl →NaCl + H2O
+NH3
Q16. What
happens when a dry strip of each of red litmus paper and blue litmus paper is
brought in contact with HCl gas? In which case a change would be observed if
the strips are moistened and then brought in contact with HCl gas and what
would be the change?
Answer
When dry red litmus and dry blue litmus
paper are brought in contact with HCl gas, no change is observed because HCl
gas does not produce H+ ions in the absence of water.
If the strips are moistened and then brought in contact with HCl gas then
i. Moist red litmus does not show change
ii. Moist blue litmus turn into red because HCl dissolves in water present on the moist litmus paper and produces H+ ions which show acidic properties.
Q17. A small palette of NaOH is kept on dry red
litmus paper. Initially, no change is observed but after some time its colour
starts changing to blue around the place where the palette of NaOH is kept.
Explain these observations.
Answer
Initially, no change is observed because
dry NaOH does not produce OH- ions in the absence of water.
After some time, NaOH absorbs moisture
from the air and dissolves in it. The dissolved NaOH dissociates to produce OH-
ions which show basic character and the red litmus paper turns blue
around the place where the NaOH palette is kept.
Q18. How does
water help in dissociation of acids and bases? Explain.
Answer
Water helps in the dissociation of acids ands bases by weakening the forces that hold their ions together. As a result, acids and bases break up into ions in aqueous solution.
i. Acids dissociate in water to produce H+ ions.
ii. Bases dissociate in water to produce OH- ions.
Therefore, acids and bases show their
acidic and basic properties only in the presence of water.
Q19. What is
‘self-dissociation of water’? Name the resulting species and give their
concentrations at 25ºC.
Answer
The process in which water molecules
dissociate on their own to produce ions in called self-dissociation of water.
The resulting species are – H+ ions
and OH-ions
At 25ºC, the concentration of both ions
are equal
[H+] =[OH-]= 1.0 ×10-7
mol L-1
Thus, pure water contains equal
concentration of H+ and OH- ions at 25ºC.
Q20. What is
ionic product constant of water? Give its value at 25ºC. will the value change
if an acid, base or salt is dissolved in water?
Answer
The product of the concentration of H+
ions and OH- ions in water at a given temperature is called the
ionic product constant of water (Kw).
At 25ºC
Kw = [H+] [OH-]=
1.0 ×10-14
When an acid, base or salt is dissolved in
water, the concentration of H+ and OH- ions may change. But their
product remains constant at a given temperature. Therefore, at 25ºC, the value
of Kw remains 1.0 ×10-14.
21. Give the relationships between the concentrations of
hydrogen ions and hydroxyl ions in (i) pure water (ii) a neutral solution (iii)
an acidic solution and (iv) a basic solution.
Answer
|
Solution |
Concentration |
|
Pure water |
[H+]=[OH-] |
|
Neutral solution |
[H+]=[OH-] |
|
Acidic solution |
[H+]>[OH-] |
|
Basic solution |
[H+]<[OH-] |
At 25ºC, pure water and natural solutions
have equal concertation of both ions. Acidic solutions contain more H+
ions and basic solutions contains more OH- ions.
22. What is pH? What happens to the pH if the hydroxyl ion
concentration in the solution increases?
Answer
pH is the negative logarithm of the
hydrogen ion concentration of a solution. It is a measure of the acidic or
basic nature of a solution.
pH= -log[H+]
if the hydroxyl ion concentration in a
solution increases, the concentration of hydrogen ions decreases. As a result,
the pH increases and the solution becomes more basic.
23. Predict whether a given aqueous solution is acidic, basic
or neutral if its pH is
(a) 7.0, (b) 11.9 and (c)
3.2.
Answer
pH 7.0 = Neutral
pH 11.9 = Basic
pH 3.2 = Acidic
24. Calculate the pH of 1.0 ×10–4 molar solution of HNO3.
Answer
HNO3 is a strong acid and
dissociates completely in water.
Therefore
[H+]= 1.0 ×10-4 mol
L-1
pH=
-log[H+]
pH= -log[1.0 ×10-4]
pH= 4
25. What is the pH of 1.0 × 10-5 molar solution of
KOH?
Answer
KOH is a strong base and dissociates
completely in water.
Therefore
[OH-] = 1.0 × 10-5
mol L-1
pOH = -log [OH-]
pOH = -log [1.0 × 10-5] =5
pH+pOH =14
pH = 14-5=9
The pH of the 1.0 × 10-5 molar
solution of KOH is 9.
26. What is the pH of 1.0 × 10-2 mol L-1
solution of NaCl?
Answer
NaCl is a salt formed from a strong acid
and a strong base. Its aqueous solution is neutral.
In a neutral solution
[H+]=[OH-]= 1.0 × 10-7
mol L-1
Therefore
pH= -log(1.0 ×10-7)=7
The pH of 1.0 × 10-2 mol L-1
NaCl solution is 7.
27. What do you understand by the term ‘universal indicator’?
Answer
A
universal indicator is a mixture of several indicators that shows a different
characteristic colour at different pH values. It is used to determine the
approximate pH of a solution and whether the solution is acidic, basic or
neutral.
28. What is acid rain?
Answer
Acid rain is rainwater whose pH is less
than 5.6 due to the presence of acidic pollutants in the atmosphere. It is
harmful to plants, animals, buildings and the environment.
29. What is the importance of pH for humans and animals, and
our digestive system?
Answer
i. Most of the biochemical processes in humans and animals takes place in pH range of 7.0 to7.8. The change in pH disturbs these processes.
ii. Hydrochloric acid is produced in our stomach which give acidic medium for the functioning of digestive enzymes.
Q30.Which chemical causes pain and burning sensation when somebody accidentally touches ‘nettle plant’?
Answer
Methanoic acid (Formic acid)
31.What is a salt? Give two examples.
Answer
A salt is an ionic compound made up of a cation (other than H+) and anion (other than OH-). Salts are generally formed during a neutralisation reaction between acid and a base.
Examples – NaCl and CuSO4
32. How are salts obtained from an acid? Mention four types of substances that can be used for it.
Answer
Salts are obtained from an acid by reacting it with different substances. The following four types of substances can be used:
i. Metals
ii. Bases
iii. Metal oxides
iv. Metal carbonates/ metal hydrogen carbonates
These reactions produce salts along with
other products such as hydrogen gas, water or carbon dioxide depending on the
substances used.
Example
Acid + metal → salt + hydrogen
Acid +
Base → salt + water
Acid + metal oxide → salt + water
Acid + metal carbonate → salt + water +
carbon dioxide
33. Give chemical formula of (i) baking soda and (ii) washing
soda.
Answer
(i) Baking soda- NaHCO3
(ii) Washing soda- Na2CO3.10H2O
34. List the raw materials required for the manufacture of
baking soda and describe the process with the help of suitable chemical
equations.
Answer
Raw Materials
Sodium
chloride
Ammonia
Carbon dioxide
Water
Process of Manufacture
A concentrated solution of sodium
chloride(Brine) is saturated with ammonia gas.
Carbon dioxide is passed through ammoniated
brine. As a result, sodium hydrogen carbonate is formed which is separated as
precipitate.
NaCl + NH3 +CO2 + H2O→NaHCO3
+ NH4Cl
The precipitated sodium hydrogen carbonate
is filtered, washed and dried to obtain baking soda.
35. Distinguish between baking powder and baking soda. Why is
baking powder preferred for making cakes?
Answer
|
Baking soda |
Baking powder |
|
It is sodium
hydrogen carbonate. |
It is a mixture
of sodium hydrogen carbonate and a mild tartaric acid. |
|
On heating, it produces
CO2 along with sodium carbonate. |
On heating or
mixing with water, it produces CO2 without leaving a bitter
residue. |
|
It may leave a
bitter taste due to formation of sodium carbonate |
It does not
leave a bitter taste because the acid neutralizes the sodium carbonate. |
36. Give any two uses of baking soda.
Answer
i. Used in making cakes, bread and other bakery products soft and spongy.
ii. Used as antacid to relieve acidity and indigestion.
37. What is washing soda? Give its chemical formula. How is
it manufactured by Solvay’s method?
Answer
Washing soda is sodium carbonate
decahydrate. It is an important sodium salt used as a cleaning agent.
Chemical Formula : Na2CO3.10H2O
Manufacture Method (Solvay’s method)
Sodium hydrogen carbonate is prepared by
passing carbon dioxide through ammoniated bring(NaCl solution).
NaCl + NH3 +CO2 + H2O→NaHCO3
+ NH4Cl
The sodium hydrogen carbonate is heated to
form sodium carbonate.
2NaHCO3 →Na2CO3
+ CO2 +H2O
Finally, sodium carbonate is crystallised with
water to obtain washing soda.
Na2CO3 + 10H2O → Na2CO3.10H2O
38. Give two uses of washing soda.
Answer
i. As a cleansing agent for washing clothes and household items.
ii. For removing permanent hardness of water.
39. What is the chemical formula of ‘plaster of Paris’? How
is it manufactured? What precaution is taken during its manufacture?
Answer
Plaster of Paris is calcium sulphate hemihydrate.
Chemical formula: CaSO4.
Manufacture of Plaster of Paris
Plaster of Paris is manufactured by heating
gypsum at about 373K(100ºC)
2CaSO4.2 H2O → 2CaSO4.
H2O + 3H2O
Precaution during Manufacture
The temperature should not be allowed to rise
much above 373K. on strong heating, Plaster of Paris loses all its water of
crystallization and forms anhydrous calcium sulphate, which does not set into a
hard mass when mixed with water.
40. List any four uses of ‘plaster of Paris’.
Answer
i. For making statues, toys and decorative articles.
ii. For making moulds and casts used in pottery and ceramics.
iii. For setting fractures bones in hospitals.
iv. For making false ceilings and wall finishes in buildings.
41. What is bleaching? Chemically, what is
bleaching powder? Give its any four uses.
Answer
Bleaching is the process of
removing colour form-coloured substances to make them white or colourless.
Bleaching powder is calcium oxychloride
Chemical formula: CaOCl2
Uses of bleaching powder
i. For bleaching cotton and linen in textile industry.\
ii. For bleaching wood pulp in the paper industry.
iii.For disinfecting drinking water and swimming pools.
iv. As an oxidising agent in chemical industries.
42. List the raw materials required and the method of
manufacture of bleaching powder. Write the equation for the reaction involved.
Answer
Raw materials
Slaked lime
Chlorine gas
Method of Manufacture
Bleaching powder is manufactured by
passing chlorine gas over dry slaked lime in a special chamber. Chlorine reacts
with slaked lime to form bleaching powder.
Ca(OH)2 + Cl2 → CaOCl2
+ H2O
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