Chapter 2 Acids, Bases and Salts
.jpg "RBSE Solutions for Class10 Science Chapter 2 Acids ,Bases and Salts")
If you are preparing
for RBSE class 10 board exams, then these solutions of intext and end exercise
questions will help you a lot.
All answers have been
explained in detail.
|
Board |
RBSE |
|
Subject |
Science |
|
Chapter |
Acids, Bases and Salts |
|
No. of Intext
questions |
19 |
|
No. of End exercise
questions |
15 |
|
Prescribed Book |
NCERT Science |
Acids,Bases and Salts Questions - Answers
Answers of Questions on Page 18
Q.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?
Ans- We can follow these steps to identify the
contents of each test tube.
1. We will dip the red litmus paper in all the
test tubes.
2. The test tube in which red litmus changes to
blue, contains basic solution.
3. Now we dip the so changed ‘blue litmus paper’
in other two tests tubes.
4. The
test tube in which blue litmus changes
to red is acidic solution.
5. The third
test tube will contain distilled water.
Answers of Questions on Page 22
Q.1 Why
should curd and sour substances not be kept in brass and copper vessels?
Ans.:- When they are kept in brass and copper vessels,
the metal reacts with the ‘acid’ present in curd and other sour substances
liberate hydrogen gas and harmful products and food items get spoiled, that’s
why it is advised not to store curds and other sour substances in the brass or
copper vessels.
Q.2 Which
gas is usually liberated when an acid reacts with a metal? Illustrate with an
example. How will you test the presence of the gas?
Ans.When an acid reacts with a metal, Hydrogen gas is
liberated.
We will take
few pieces of zinc granules and add 5 ml of dilute H2SO4.
After some time a gas is produced which is passed into a soap solution. The
bubbles of the soap solution are formed. These soap bubbles contain hydrogen gas.
.webp "reaction of acids with metals produces hydrogen")
When we take a burning candle near bubbles, they burst
with pop sound which prove that evolving gas is Hydrogen.
Zn + 2H2SO4 → Zn(SO4)2+
2H2↑
Q.3 A
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 when one of the compounds formed is calcium chloride.
Ans.Metal compound ‘A’ reacts with dilute hydrochloric
acid to form a gas which extinguishes burning candle means produced gas is carbon
dioxide. Other product is calcium chloride, so compound A is carbonate of
calcium.
CaCO3
+ 2HCl → CaCl2 + H2O
+ CO2
Answers of Questions on Page 25
Q.1 Why
do HCl, HNO3 etc. show acidic character in aqueous solutions while solutions of
compounds like C2H5OH and glucose do not show acidic character?
Ans. HCl,
HNO3 show acidic character in aqueous solutions because they produce
H+ (aq) ions, although aqueous solutions of glucose and alcohol contain
hydrogen but they do not produce hydrogen
ions in water. That’s why they do not
show acidic character.
The dissociation of HCl or HNO3 to form hydrogen ions
always occurs in the presence of water. Hydrogen ions (H+) combine with H2O to
form hydronium ions (H3O+).
HCl(aq) → H+ + Cl-
H+ + H2O → H3O+
Q.2 Why
does an aqueous solution of acid conduct electricity?
Ans.An aqueous solution of an acid has cations and
anions, that conducts electricity. These ions are responsible for conduction of
electricity.
Q.3 Why
does dry HCl gas not change the colour of dry litmus paper?
Ans. Hydrogen ions (H+) are formed in the presence of
water only and these ions are responsible for acidic character of HCl and
change of litmus paper. So dry HCl does not produce H + with dry litmus paper, that’s why, dry HCl
gas cannot change the colour of dry litmus paper.
Q.4 While
diluting the acid why is it recommended that acid should be added to water and
not the water to the acid?
Ans. The diluting of an acid is an exothermic
reaction. When small amount of water is added to acid, water gets converted
into vapours due to heat.
So acid with water vapour spill and may cause injury
That’s why it
is always recommended that acid should be added to water.
Q.5 How
is the concentration of hydronium ions (H3O+ ) affected when a
solution of an acid is diluted?
Ans. When a
solution of an acid is diluted, the concentration of hydronium ions (H3O+) is decreased.
Q.6 How
is the concentration of hydroxide ions (OH-) affected when excess base is
dissolved in a solution of sodium hydroxide?
Ans. When
excess base is dissolved in a solution hydroxide, the concentration of hydroxide (OH-) ions would increase.
Answers of Questions on Page 28
Q.1 You
have two solutions A and B. pH of solution A is 6 and pH of solution B is 8.
Which solution has more hydrogen ion concentration? Which of these is acidic
and which one is basic?
Ans. According to PH scale , the pH value less than 7 indicates an acidic solution,
while greater than 7 indicates a basic solution.
So, the
solution with PH = 6 is acidic and the solution of PH =
8 is basic. Concentration of hydrogen
ions increases with PH below 7
So solution A
with PH 6 has more hydrogen
ions than solution B .
Q.2 What
effect does the concentration of H+ (aq) have on the acidic nature of the
solution?
Ans.The concentration of H+ (aq) is directly
proportional to the acidic nature of the solution. More concentration of H+
(aq) ions, means more acidic nature and less concentration of H+ (aq) ions
means less acidic nature of solution.
Q.3 Do
basic solution also have H+ (aq) ions? If yes, then why are they basic?
Ans.Yes, basic solution also has H+ ions. But their concentration is less as
compared to the concentration of OH- ions, that’s why they are basic in nature.
Q.4 Under
what soil conditions do you think a farmer would spread or treat the soil of
his fields with quick lime (calcium oxide) or slaked lime (calcium hydroxide)
or chalk (calcium carbonate).
Ans. If the
soil is acidic and improper for cultivation, then to increase the basicity of
soil, the farmer would treat the soil with quick lime or slaked lime or chalk
because Quick lime, slaked lime and chalk are basic in nature
Answers of Questions on Page 33
Q.1 What
is the common name of compound CaOCl2?
Ans. Bleaching
powder.
Q.2 Name
the substance which on treatment with chlorine, yields bleaching powder?
Ans. Dry
slaked lime [Calcium hydroxide (Ca (OH)2]
Q.3 Name
of sodium compound which is used for softening of hard water.
Ans. Washing
soda [sodium carbonate (Na2CO3.10H2O)] is used
for softening of hard water.
Q.4 What
will happen if the solution of sodium hydrogen carbonate is heated?
Ans. On
heating sodium hydrogen carbonate changes to sodium carbonate.
2NaHCO3 → Na2CO3 +H2O + CO2↑
Q.5 Write
an equation to show the reaction between plaster of Paris and water.
Ans. CaSO4 .
(Plaster
of Paris) ( Gypsum)
Answers of Questions End EXERCISES
Q.1 A solution turns red litmus blue, its pH is likely to be
(a) 1 (b) 4 (c) 5 (d) 10
Ans. (d) 10
Q.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
Ans. (d) HCl
Q.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 same solution of NaOH, the amount of
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
Q.4 Which
one of the following types of medicines is used for treating indigestion?
(a) Antibiotic (b) Analgasic
(c) Antacid (d) Antiseptic
Ans. (d) Antacid
Q.5 Write
word equation and then balanced equation 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) Sulphuric
acid + Zinc → Zinc sulphate + Hydrogen
H2
SO4(aq) + Zn(s) → ZnSO4(aq) + H2(g)
(b) Hydrochloric acid + Magnesium → Magnesium
chloride + Hydrogen
2HCl(aq) + Mg(s) → MgCl2(aq) + H2(g)
( c) Sulphuric
acid + Aluminium → Aluminium sulphate + Hydrogen
3H2SO4(aq) +
2Al(s) → Al2(SO4)3
(aq) + 3H2(g)
(d)Hydrochloric
acid + Iron → Ferric chloride + Hydrogen
6HCl(aq)
+ 2Fe(s) →
2FeCl3(aq) + 3H2(g)
Q.6 Compounds
like alcohol and glucose also contain hydrogen but are not catergorised as
acids. Describe an activity to prove it.
Ans. Object-
Hydrogen ion present in acids is ionic while hydrogen ion in alcohol, glucose
is not ionic
Method- At first we
prepare aqueous solutions of alcohol, glucose, hydrochloric acid. Now we take a
100ml capacity beaker and two nails are fitted on a cork and in it. The nails are then connected to the two
terminals of a 6-volt battery, ammeter, a torch bulb and switch through a bulb
and a switch. Some dilute HCl is poured in the beaker and the current is
switched on. The same experiment is then performed with glucose solution and
alcohol solution.
.webp "acids,bases and salts questions answers")
Observations:
It will be observed that the bulb glows in the HCl
solution and does not glow in the glucose solution.
Result:
HCl dissociates into H+ and Cl- ions. These ions
conduct electricity in the solution resulting in the glowing of the bulb. On
the other hand, the glucose solution does not dissociate into ions. So, it does
not conduct electricity.
Q.7 Why
does distilled water not conduct electricity whereas rain water does?
Ans. Distilled
water is a pure form of water and it does not have any ions in it and ions are responsible for conduction of
electricity. Therefore, it does not conduct electricity but on the other hand rain-water dissolve
atmospheric carbon dioxide to form carbonic acid (H2CO3) which form H+ ions and
due to presence of H+ ions, rain water conducts electricity, but a distilled
water cannot.
Q.8 Why
do acids do not show acidic behaviour in the absence of water?
Ans. Hydrogen ions are responsible for acidic
character. Acids produce Hydrogen
ions in water only and these ions are not produced in dry acids. so, acid do
not show acidic behavour in the absence of water.
Q.9 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.
|
Solutions
|
Showing
PH |
|
Neutral |
7 (solution –D) |
|
Strongly
alkaline |
11(solution- C) |
|
Strongly acidic |
1(solution – B) |
|
Weakly acidic |
4 (solution – A) |
|
Weakly alkaline |
9 (solution – E) |
PH in increasing order of hydrogen ion
concentration 11 < 9 < 7 < 4 < 1.
Q.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 (CH3COOH) is added to test tube
B. in which test tube will the fizzing occur more vigorously and why?
Ans. The
fizzing will occur more vigorously in test tube A because HCl is a strong acid
and it produces more number of H+ ions whereas acetic acid is a week acid.
Q.11 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 changes to curd it pH will decrease below the value of 6 due to the
formation of lactic acid.
Q.12 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 to set as curd?
Ans.
(a)The milkman shifts the pH of the fresh milk from 6
to slightly alkaline by adding small amount of baking soda, because in alkaline
condition, milk does not set as curd easily.so that it may take time to
lower pH of lactic acid.
(b)By the
action of microorganisms, lactic acid is formed which has pH about 3, but
When baking
soda is added to this, pH of milk goes above 7, due to this acid in the milk is
neutralized by the base. Therefore, it
takes a longer time for the curd to set.
Q.13 Plaster
of Paris should be stored in a moisture-proof container. Explain why?
Ans. Plaster of Paris changes to a hard substance reacting with water. That’s why; it is stored in a moisture-proof container.
CaSO4
.
(Plaster of
Paris) ( Gypsum- Hard solid
substance)
Q.14 What
is a neutralization reaction? Give two examples.
Ans. When
an acid and base react with each other to give a salt and water istermed as
neutralization reaction. In this reaction, energy is evolved in the form of
heat.
NaOH + HCl →
NaCl + H2O
Q.15 Give
two important uses of washing soda and baking soda.
Ans.
1) Washing soda (Na2CO3.10H2O)
It is used in glass, soap, and paper industries.
It is used to remove permanent hardness of water.
(2) Baking soda (NaHCO3)
It is used as baking powder. Baking powder is a
mixture of baking soda and a mild acid known as tartaric acid.
It is used in soda-acid fire extinguisher
These RBSE solutions are based on NCERT Class 10
Science book so these can be very useful those students who are studying through
NCERT books.
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