Solutions-Class 8-Science-Chapter-12-Introduction to Acid and Base-Maharashtra Board

Introduction to Acid and Base

Maharashtra Board Class 8- General Science - Chapter-12

Solution

Question 1:

Identify the following solutions, whether they are acid or alkali.

Solution Change in Indicator Acid/Alkali
  Litmus Phenolphthalein Methyl orange  
1. ... No change ...  
2. ... ... Orange colur turns red  
3. Red litmus turns blue ... ...  

Answer

 

Solution Change in Indicator Acid/Alkali
  Litmus Phenolphthalein Methyl orange  
1. No change Acid
2. Orange colour turns red Acid
3. Red litmus turns blue Alkali

Question 2:

Write chemical names from given formulae.
H2SO4,   Ca(OH)2,    HCl,  NaOH,  KOH, NH4OH

Answer

H2SO4 = Sulphuric Acid

Ca(OH)2 = Calcium hydroxide
HCl = Hydrochloric Acid

NaOH = Sodium hydroxide

KOH = Potassium hydroxide

NH4OH = Ammonium hydroxide

Question 3:

Sulphuric acid has highest importance in chemical industry. Why?

Answer

Sulphuric acid has highest importance in chemical industry because

  • Sulphuric acid is used in manufacturing fertilizers such as super phosphate, ammonium sulphate etc.
  • Sulphuric acid is used in the manufacture of dyes.
  • Sulphuric acid is used in the manufacture of Nitric acid, Hydrochloric Acid, Tannic acid.
  • Sulphuric acid is used in the manufacture of drugs.
  • Sulphuric acid is used in the manufacture of explosives.
  • Sulphuric acid is used in batteries, which is used in all type of vehicles.
  • Hydrochloric acid is used to make aqua regia, which is used to dissolve noble metals such as gold and platinum.
  • Sulphuric acid is used in the manufacture of jet fuel, kerosene and leather.

Question 4:

Give answers
1. Which acid is used for getting chloride salt ?

Answer

Hydrochloric Acid (HCL) is used for getting chloride salt because this acid provides chloride ion to form chloride salt.
For example :
HCl + NaOH→ NaCl + H2O

2. By squizzing lemon on a piece of rock the gas liberated turned lime water milky. which compound is present in the rock ?

Answer

Metal Carbonate presents in the rock. Because Acids react with carbonate or bicarbonate and liberate CO2. This carbon dioxide turns lime water milky.

3. The label on the bottle of chemical is spoiled. How will you find whether the chemical is acidic or not ?  

Answer

We can find out the chemical is acidic or not, by two ways :
1.By use of litmus paper :

  • If the given solution is acidic, it turns blue litmus  to red litmus. 
  • If the given solution is basic, it turns red litmus  to blue litmus.
  • If the given solution is neutral, there is no effect on litmus paper.

2.By use of indicators :

  • If the given solution is acidic, it turns methyl orange to red.
  • If the given solution is basic, it turns methyl orange to yellow.
  • If the given solution is neutral, there is no effect on methyl orange indicator.

Question 5:

Answer the following questions.
i. Explain the difference between acid and alkali.

Answer

Difference between acid and alkali :

Acid Alkali
1. Acid has sour taste. 1. Alkali has bitter taste.
2. Acid turns blue litmus red. 2. Alkali turns red litmus blue.

 
3. An acid in an aqueous solution gives H+ ions. 3. An alkali in an aqueous solution gives OH+ ions.
4. Oxides of non-metals form acids. 4. Oxides of metals form bases.

ii. Why indicator does not get affected by salt?

Answer

  • Mostly indicators are organic compounds which do not react with salt.
  • Indicators do not get affected by salts because salts are neutral in nature.
  • Indicators work only with acidic and basic substances.

iii. Which substances are produced by neutralization process?

Answer

Water and a salt are produced in neutralization process.

When an acid reacts with an alkali to form a salt and water, it is called neutralization.

Acid + Base → Salt + Water

HCl + NaOH→ NaCl + H2O

iv. Which are the industrial uses of acids ?

Answer

Acids which are used in the industry are :

(1) Sulphuric acid (2) Hydrochloric acid (3) Nitric acid.

Sulphuric acid: Sulphuric acid is used

  • in the manufacture of chemical fertilizers like ammonium sulphate,
  • for cleaning gold and silver articles and
  • in car batteries.

Hydrochloric acid : Hydrochloric acid is used

  • to clean toilets and
  • to obtain glucose from starch and also for producing gelatine.

Nitric acid : Nitric acid is used

  • in the manufacture of perfumes.
  • for engraving on copper, brass or silver and
  • in the manufacture of paints and explosives.

Question 6:

Select proper word given in bracket and fill in the blanks.

a. Main constituent of acid is......................

b. Main constituent of alkali is...................

c. Tartaric acid is a................ acid.

Answer

a. Main constituent of acid is H+ ion.
b. Main constituent of alkali is OH- ion.
c. Tartaric acid is a weak acid.

Question 7:

Match the pairs. 

  Group A  Group B
1. Tamarind  a. Acetic acid
2. Curd  b. Citric acid
3. Lemon  c. Tartaric acid
4.Vinegar d. Lactic acid

Answer

 

  Group A  Group B
1. Tamarind  Tartaric acid
2. Curd  Lactic acid
3. Lemon  Citric acid
4. Vinegar  Acetic acid

Question 8:

State true of false

i. Oxides of metals are alkaline in nature.

ii. Salt is acidic

iii. Metal corrodes due to salts

iv. Salts are neutral.

Answer

i. Oxides of metals are alkaline in nature = True

ii. Salt is acidic = False (Salt is neutral)

iii. Metal corrodes due to salts = False (Acids and Bases corrodes metals)

iv. Salts are neutral = True

Question 9:

Classify following substances into acidicm basic and neutral group-
HCl,   NaCl,  MgO,  KCl,  H2SO4,  HNO3,  H2O,  Na2CO3

Answer

 

Group Substances
Acid HCl, H2SO4, HNO3
Base MgO, Na2CO3
Neutral NaCl, KCl, H2O




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