Wednesday, 30 September 2015

TEXTBOOK ANSWERS AND SOLUTIONS CBSE CLASS X SCIENCE Chapter-2 Acids Bases And Salts



Exercise:- (page-34-35)

1)    A solution turns red 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

(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

(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

(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.

ANSWER: 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.

Observation-The bulb wil start glowing in the HCl solution whereas it doesnot glow in the glucose solution.

Result:-HCl dissociates into H+and Clions. 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)

7.Why 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.

8.Why do acids not show acidic behaviour in the absence of water?

ANSWER:

The dissociation of hydrogen ions from an acid
occurs in the presence of
water only 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
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 oder of hydrogen-ion concentration.

ANSWER:Neutral Solution D with pH 7
(b) Strongly alkaline Solution
C with pH 11
(c) Strongly acidic Solution
B with pH 1
(d) Weakly acidic Solution A
with pH 4
(e) Weakly alkaline Solution
E with pH 9



The pH can be arranged in the
increasing order of the
concentration of hydrogen ions
as:- 11 < 9 < 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?

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.

11.Fresh milk 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 .

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 time to set as curd?

ANSWER:-

a) The milkman shifts the pH of the fresh milk
from 6 to slightly 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.

13.Plaster of 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.

CaSO4.1/2H2O +1 1/2 H2O-->CaSO4.2H2O (refer to pg-33)

CaSO4.2H2O-Gypsum


14.What is a neutralization reaction? Give two examples.

ANSWER:-

 A reaction in which an acid and base react with
each other to give a salt and water is termed as neutralization reaction.
Examples- NaOH+HCl-->NaCl+H2O

HNO3+KOH-->KNO3+H2O

15.Give two important uses of
washing soda and baking soda.

ANSWER:-

Two uses of washing soda are- used for removing permanent hardness of water,
It is used in glass,soap and paper industries.

Two uses of baking soda- It is used in soda-acid fire
extinguishers,used as baking powder.




Written By Badal Paul
The author is a passionate blogger, writer and educationalist. This blog is created to ease troubles of the Cbse students. The author holds multiple blogs and the writer of the Novel KALCHAKRA, OOM AND THE CHOSEN FIVE.