Exercise:- (page-34-35)
1) A solution turns red
litmus blue, its pH is likely to be
litmus blue, its pH is likely to be
(a) 1 (b) 4 (c) 5 (d) 10
ANSWER:
Itz pH is likely to b 10 basic solution has a pH value
more than 7.
2. A solution reacts with crushed egg-shells to give a gas that
turns lime-water milky. The solution contains
turns lime-water milky. The solution contains
(a) NaCl (b) HCl (c) LiCl (d) KCl
ANSWER:
The solution contains 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 of HCl solution (the same
solution as before)required to neutralise it will be
take 20 mL of the same solution of NaOH, the amount of HCl solution (the same
solution as before)required to neutralise it will be
(a) 4 mL (b) 8mL (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 is used for treating indigestion
5. Write word equations and then balancedequations for the
reaction taking place when –
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) Sulphuric acid + Zinc → Zinc sulphate +Hydrogen
H2SO4+Zn—>ZnSO4+H2
(b) Hydrochloric acid + Magnesium →Magnesium chloride + Hydrogen
2HCl+Mg—>MgCl+H2
(c) Sulphuric acid + Aluminium → Aluminium sulphate + Hydrogen
3H2SO4+2Al—->Al2SO4+3H2
(d) Hydrochloric acid + Iron → Ferric chloride +Hydrogen
6HCl+2Fe—>2FeCl3+3H2
6. Compounds such as alcohols and glucose also contain hydrogen
but are not categorized as acids. Describe an activity to prove it.
but are not categorized as acids. Describe an activity to prove it.
ANSWER:
Apparatus:-Two nails are fitted on a rubber cork in a dilute HCl solution . The
nails are are connected to the two
Apparatus:-Two nails are fitted on a rubber cork in a dilute HCl solution . The
nails are are connected to the two
terminals of a 6-volt battery
through a bulb and a switch.Put on d current.the same is repeated
with alcohol and glucose solution.
with alcohol and glucose solution.
Observation-The
bulb wil start glowing in the HCl solution whereas it doesnot glow in the
glucose solution.
bulb wil start glowing in the HCl solution whereas it doesnot 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. Therefore,
it does not conduct electricity
( for
diagram refer to page number-22 figure num-2.3)
diagram refer to page number-22 figure num-2.3)
7.Why does
distilled water not conduct electricity, whereas rain water does?
distilled water not conduct electricity, whereas rain water does?
ANSWER: Distilled water is a
pure form of water it doesnot contain ions wheras rain water is an impure form
of water and contains ions therfore distilled water doesnot conduct
electricity.
pure form of water it doesnot contain ions wheras rain water is an impure form
of water and contains ions therfore distilled water doesnot conduct
electricity.
8.Why do acids
not show acidic behaviour in the absence of water?
not show acidic behaviour in the absence of water?
ANSWER:
The dissociation
of hydrogen ions from an acid
of hydrogen ions from an acid
occurs in the
presence of
presence of
water only
therefore acids do not show acidic behaviour in the absence of water.
therefore acids do not show acidic behaviour in the absence of water.
9. Five
solutions A, B, C, D and E when tested with universal
solutions A, B, C, D and E when tested with universal
indicator
showed pH as 4, 1,11 ,7 and 9, respectively.
showed pH as 4, 1,11 ,7 and 9, respectively.
Which solution
is
is
(a) neutral?
(b) strongly
alkaline?
alkaline?
(c) strongly
acidic?
acidic?
(d) weakly
acidic?
acidic?
(e) weakly alkaline?
Arrange the pH
in increasing oder of hydrogen-ion concentration.
in increasing oder of hydrogen-ion concentration.
ANSWER:Neutral →Solution
D with pH 7
D with pH 7
(b) Strongly
alkaline →Solution
alkaline →Solution
C with pH 11
(c) Strongly
acidic →Solution
acidic →Solution
B with pH 1
(d) Weakly acidic
→Solution A
→Solution A
with pH 4
(e) Weakly alkaline
→Solution
→Solution
E with pH 9
The pH can be
arranged in the
arranged in the
increasing order
of the
of the
concentration of
hydrogen ions
hydrogen ions
as:- 11 < 9
< 7 < 4 < 1
< 7 < 4 < 1
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?
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?
ANSWER:-
The fizzing occur more vigorously in test
tube A on which HCl is added as because HCl is stronger than CH3COOH and
produces hydrogen gas at a faster rate
and therfore freezing occurs.
tube A on which HCl is added as because HCl is stronger than CH3COOH and
produces hydrogen gas at a faster rate
and therfore freezing occurs.
11.Fresh milk
has a pH of 6. How do you think the pH will change as it turns into curd?
Explain your
has a pH of 6. How do you think the pH will change as it turns into curd?
Explain your
answer.
ANSWER:- As the
curd is acidic in nature the pH will reduce .
curd is acidic in nature the pH will reduce .
12.A milkman
adds a very small amount of baking soda to fresh milk.
adds a very small amount of baking soda to fresh milk.
(a) Why does he
shift the pH of the fresh milk
shift the pH of the fresh milk
from 6 to
slightly alkaline?
slightly alkaline?
(b) Why does
this milk take a long time to set as curd?
this milk take a long time to set as curd?
ANSWER:-
a) The milkman
shifts the pH of the fresh milk
shifts the pH of the fresh milk
from 6 to slightly
alkaline because in alkaline condition, milk does not set as curd easily.
alkaline because in alkaline condition, milk does not set as curd easily.
b) Since this
milk is slightly basic than usual milk acids produced to set the curd are
neutralized by the base. Therefore, it takes longer time for the curd to set.
milk is slightly basic than usual milk acids produced to set the curd are
neutralized by the base. Therefore, it takes longer time for the curd to set.
13.Plaster of
Paris should be stored in a moisture-proof container. Explain why?
Paris should be stored in a moisture-proof container. Explain why?
ANSWER:-
Plaster of paris
is a white powder and on mixing with powder changes to gypsum therefore it
should be stored in a moisture proof container.
is a white powder and on mixing with powder changes to gypsum therefore it
should be stored in a moisture proof container.
CaSO4.1/2H2O +1
1/2 H2O–>CaSO4.2H2O (refer to pg-33)
1/2 H2O–>CaSO4.2H2O (refer to pg-33)
CaSO4.2H2O-Gypsum
14.What is a
neutralization reaction? Give two examples.
neutralization reaction? Give two examples.
ANSWER:-
A reaction in which an acid and base react
with
with
each other to
give a salt and water is termed as neutralization reaction.
give a salt and water is termed as neutralization reaction.
Examples-
NaOH+HCl–>NaCl+H2O
NaOH+HCl–>NaCl+H2O
HNO3+KOH–>KNO3+H2O
15.Give two
important uses of
important uses of
washing soda
and baking soda.
and baking soda.
ANSWER:-
Two uses of
washing soda are- used for removing permanent hardness of water,
washing soda are- used for removing permanent hardness of water,
It is used in
glass,soap and paper industries.
glass,soap and paper industries.
Two uses of
baking soda- It is used in soda-acid fire
baking soda- It is used in soda-acid fire
extinguishers,used
as baking powder.
as baking powder.