DAV Class 7 Science Chapter 4 Question Answer – Acids, Bases and Salts

The DAV Class 7 Science Book Solutions Pdf and DAV Class 7 Science Chapter 4 Question Answer – Acids, Bases and Salts are essential study tools for DAV public school students in Class 7.

DAV Class 7 Science Ch 4 Question Answer – Acids, Bases and Salts

DAV Class 7 Science Ch 4 Solutions – Acids, Bases and Salts

Something To Know

A. Fill in the blanks.

Question 1.
Acids which are present in plants and animals are called ________
Answer:
Organic acid

Question 2.
Bases taste ________ and have a ________ feel.
Answer:
Bitter, soapy

Question 3.
Acid turns the colour of blue litmus paper to ________
Answer:
Red

Question 4.
The products of a neutralization reaction are ________ and ________
Answer:
Salt, Water

Question 5.
Salts of nitric acid (HNO₃) are named as ________
Answer:
Nitrate

Question 6.
Sodium acetate (CH₃COONa) is a basic salt formed by the reaction of ________ and________
Answer:
Acetic acid, Sodium hydroxide

B. Match the following:

Column A	Column B
1. Lemon juice	(a) Oxalic acid
2. Tamarind	(b) Lactic acid
3. Vinegar	(c) Citric acid
4. Red ants	(d) Acetic acid
5. Sour milk	(e) Tartaric acid
6. Guava	(j) Formic acid

Answer:

Column A		Column B
1. Lemon juice	c	(a) Oxalic acid
2. Tamarind	e	(b) Lactic acid
3. Vinegar	d	(c) Citric acid
4. Red ants	j	(d) Acetic acid
5. Sour milk	a	(e) Tartaric acid
6. Guava	b	(j) Formic acid

C. Tick (✓) the correct option.

1. Bases have a
(a) Bitter taste and a rough feel
(b) Sour taste and a rough feel
(c) Bitter taste and a soapy feel
(d) Sour taste and a soapy feel
Answer:
(c) Bitter taste and a soapy feel

2. An example of a natural indicator is
(a) Methyl orange
(b) Ink
(c) Phenolphthalein
(d) Litmus
Answer:
(d) Litmus

3. An acid, that contributes to the sour taste of some fruits, is
(a) Hydrochloric acid
(b) Sulphuric acid
(c) Citric acid
(d) Nitric acid
Answer:
(c) Citric acid

4. Which of the following is a strong acid?
(a) Acetic acid
(b) Citric acid
(c) Nitric acid
(d) Carbonic acid
Answer:
(c) Nitric acid

5. Substances, produced through a chemical reaction between acids and bases, are known as
(a) Salts
(b) Indicators
(c) Antacids
(d) Alkalies
Answer:
(a) Salts

6. An indicator, that turns red in a basic medium, is
(a) Turmeric
(b) Phenolphthalein
(c) Blue litmus
(d) Hibiscus
Answer:
(a) Turmeric

7. The general taste, of acids and bases, is respectively
(a) Sweet and salty
(b) Sour and salty
(c) Sour and sweet
(d) Sour and bitter
Answer:
(d) Sour and bitter

D. Answer the following questions in brief.

Question 1.
What are mineral acids?
Answer:
Acids which are prepared from minerals are called mineral acids.

Question 2.
Give two examples each of mineral acids and organic acids.
Answer:
Mineral acids: Sulphuric acid and nitric acid
Organic acids: Acetic acid and citric acid

Question 3.
Name any two substances that can be used as indicators.
Answer:
Turmeric and litmus

Question 4.
Write the meaning of the term ‘neutralisation reaction.’
Answer:
A reaction between an acid and a base which produces salt and water is called neutralisation reaction.

Question 5.
Give any two properties of salts.
Answer:
Properties of salts:

• Salts are formed after neutralisation reaction.
• Most of the salts are readily soluble in water.
• Salts are bad conductors of electricity in their solid state. Molten salts and solution of salt in water are good conductors of electricity.

Question 6.
Classify the following salts as neutral, acidic or basic. Also, write their names.
(a) Na₃PO₄
(b) K2CO₃
(C) NH₄NO₃
Answer:
(a) Sodium phosphate: neutral salt,
(b) Potassium carbonate: Basic salt,
(c) Ammonium nitrate: Acidic salt

E. Answer the following questions.

Question 1.
‘All alkalies are bases but all bases are not alkalies’, justify this statement.
Answer:
Those bases which are soluble in water are called alkalis, but not all of the bases are soluble in water. Hence, it can be said that all alkalis are bases but all bases are not alkalis.

Question 2.
Suggest an activity that can help one to decide whether a given solution is acidic or basic in nature.
Answer:
For this, take blue and red litmus papers and a test tube. Take the given solution in a test tube. Dip the blue and red litmus paper; one by one; in the test tube. If the blue litmus paper changes to red then the given solution is acidic. If the red litmus paper turns blue then the given solution is basic.

Question 3.
Write chemical equations for the following reactions:
(a) Calcium hydroxide reacts with nitric acid.
Answer:
Ca(OH)₂ + 2HNO₃ → Ca(NO₃)₂+ 2H₂O

(b) Acetic acid reacts with calcium hydroxide.
Answer:
2CH₃COOH + Ca(OH)₂ -> Ca(CH₃COO)₂+ 2H₂O

(c) Hydrochloric acid reacts with sodium hydroxide.
Answer:
HCl + NaOH → NaCl + H₂O

(d) Ammonium hydroxide reacts with sulphuric acid.
Answer:
2NH₄OH + H₂SO₄ → (NH₄)₂SO₄ → 2H₂O

Question 4.
State the difference between neutral, acidic and basic salts. Give one example of each.
Answer:

Neutral salt	Acidic salt	Basic salt
Formed after reaction between strong acid and strong base.	Formed after reaction between strong acid and weak base.	Formed after reaction between weak acid and strong base.
Example: Sodium chloride	Example: Ammonium sulphate	Example: Sodium acetate

Question 5.
Describe an activity to show that solutions of salts, in water, can conduct electricity.
Answer:
Take a beaker and fill it half with water. Dissolve some common salt (sodium chloride) in this water. Connect two graphite rods with the two terminals of a battery, with a zero watt LED bulb in between, as shown in the figure. Now dip these graphite rods in the solution of sodium chloride. The bulb starts glowing indicating the flow of electric current. This shows that a solution of sodium chloride can conduct electricity.

Value Based Question

The Physical Training (PT) teacher noticed that two of her students were having very heated arguments with each other. She immediately went to them, calmed them down and made them sit together. She listened patiently to both of them and then explained to them the merits, of the ‘other point of view’ and the impor¬tance of ‘team work’. The students agreed to follow her advice and instructions. The chemistry teacher, who was watching all this, remarked that she sees a lot of similarity between the role of the PT teacher and the ‘neutralisation reactions’ between acids and bases.

Question 1.
State the values displayed by the PT teacher.
Answer:
Concern for students, friendly behaviour towards students

Question 2.
Do you agree with the remarks of the chemistry teacher? Give reason.
Answer:
The chemistry teacher has made correct remark. Just as a neutralisation reaction calms down the acidity and alkalinity of acid and base, the PT teacher is calming down the. anger of her students.

Question 3.
Write the chemical equations for two neutralisation reactions, giving names of all the compounds relevant to the reaction.
Answer:

Something To Do

Question 1.
Common names of some substances are given below. Find out the chemical formulae, chemical names and the uses of these substances, and write them in the table given below:
Answer:

Common name	Formula	Chemical name
Caustic soda	NaOH	Sodium Hydroxide	In industry; for making paper, textiles, detergents, etc.
Caustic potash	KOH	Potassium hydroxide	In soap making
Baking soda	NaHCO3	Sodium bicarbonate	In bakeries; for making bread and cake
Washing soda	NaCO3	Sodium carbonate	In softening of water, for washing clothes and utensils
Limestone	CaCO3	Calcium carbonate	Building material, whitewashing
Quicklime	CaO	Calcium oxide	In industry; for making some chemicals
Lime water	Ca(OH)3	Calcium hydroxide	In industries (as cleansing agent for harmful gases), in making some dishes
Plaster of Paris	CaSO42H2O	Calcium sulphate	In making plaster cast to fix broken bones, in making sculpture, building material
Blue vitriol (neelaa thotha)	CuSO4	Copper sulphate	As fungicide, insecticide and as a dye

Question 2.
Solve the crossword puzzle with the help of the clues given below:

Across:
1. A basic salt present in washing powders.
4. A weak acid present in vinegar.

Down:
2. An acid whose salts are called sulphites.
3. A substance used to reduce acidity in our stomach.
5. An acid present in oranges and lemons.

Question 3.
Some acids, bases and salts are commonly used in our daily life. Find out the names of such substances, specify whether they are acids, bases and salts and write their uses.
Answer:
Do it yourself.

DAV Class 7 Science Chapter 4 Solutions – Acids, Bases and Salts

I. Fill in the blanks.

Question 1.
An acid tastes ________
Answer:
Sour

Question 2.
A base tastes ________
Answer:
Bitter

Question 3.
Litmus is made from ________
Answer:
Lichen

Question 4.
Blue litmus turns red in ________ solution.
Answer:
Basic

.

Question 5.
Red litmus turns blue in ________ solution.
Answer:
Blue

Question 6.
Chemical name of caustic soda is ________
Answer:
Sodium hydroxide

Question 7.
Chemical name of baking soda is
Answer:
Sodium bicarbonate

Question 8.
Bases taste ________and acid tastes
Answer:
Bitter, Sour

Question 9.
Bases which are soluble in water are called _______
Answer:
Alkali

Question 10.
Acids present in plants and animals are called ________
Answer:
Organic acid

II. Tick (✓) the correct option.

1. Which of these is a strong acid?
(a) Nitric acid
(b) Citric acid
(c) Acetic acid
(d) Formic acid
Answer:
(a) Nitric acid

2. Which of these is a weak acid?
(a) Sulphuric acid
(b) Sulphurous acid
(c) Carbonic acid
(d) Tartaric acid
Answer:
(d) Tartaric acid

3. Alkali is a base which is soluble in which of these solvents?
(a) Kerosene
(b) Water
(c) Milk
(d) Limewater
Answer:
(b) Water

4. What is the colour of turmeric in basic solution?
(a) Red
(b) Blue
(c) Green
(d) Colourless
Answer:
(a) Red

5. What is the colour of phenolphthalein in acidic solution?
(a) Purple
(b) Red
(c) Blue
(d) Colourless
Answer:
(d) Colourless

6. Plaster of Paris is a salt of which acid?
(a) Sulphuric acid
(b) Nitric acid
(c) Hydrochloric
(d) Carbonic acid
Answer:
(a) Sulphuric acid

III. Answer the following questions.

Question 1.
What do you understand by organic acids?
Answer:
Acids which are naturally occurring and are found in plants and animals are called organic acids. Examples: Formic acid (HCOOH), Acetic acid (CH₃COOH). Organic acids are weak acids.

Question 2.
What is an acid base indicator?
Answer:
An indicator is a substance which shows different colours in an acidic and a basic medium. Indicators help in identifying acids and bases.

Question 3.
What is a neutral salt?
Answer:
Neutral Salts: When a salt is formed after the reaction between a strong acid and a strong base, it is called a neutral salt. The aqueous solution of a neutral salt is neutral, i.e. it shows neither acidic nor basic property. Sodium chloride (NaCl), Potassium chloride (KCl), Potassium nitrate (KNO₃), Sodium sulphate (Na₂SO₄), etc. are examples of neutral salt.

Question 4.
What is an acidic salt?
Answer:
Acidic Salt: When a salt is formed after the reaction between a strong acid and a weak base, it is called an acidic salt. The aqueous solution of an acidic salt is acidic. Aluminium chloride (AlCl₃), Ammonium nitrate (NH₄NO₃), Zinc sulphate (ZnSO₄) and Copper chloride (CuCl₂) are examples of acidic salt.

Question 5.
What is a basic salt?
Answer:
Basic Salt: When a salt is formed after the reaction between a weak acid and a strong base, it is called a basic salt. The aqueous solution of a basic salt is basic. Sodium acetate (CH₃COONa), Sodium formate (HCOONa) and Sodium carbonate (Na₂CO₃) are examples of basic salt.

Question 6.
What is a neutralisation reaction? Give an example.
Answer:
The reaction between an acid and a base is called neutralisation reaction. Salt and water are formed after neutralisation reaction. One example of neutralisation reaction is given below.

In this reaction, sodium hydroxide (a base) is reacting with hydrochloric acid. As a result, sodium chloride (a salt) and water are formed.

IV. What happens when

Question 1.
Calcium oxide reacts with hydrochloric acid?
Answer:
Calcium chloride and water are formed.

Question 2.
Aluminium hydroxide reacts with hydrochloric acid?
Answer:
Aluminium chloride and water are formed.

Question 3.
Acetic acid reacts with calcium hydroxide?
Answer:
Calcium acetate and water are formed.

Question 4.
Hydrochloric acid reacts with sodium hydroxide?
Answer:
Sodium chloride and water are formed.

V. Projects

Question 1.
Make indicator paper strips by using turmeric solution. With this, test various acids and bases in your kitchen and write your observations.
Answer:
Do it yourself.

Question 2.
Make a report on olfactory indicators. Give their definition, name and benefits.
Answer:
Do it yourself.