Science In Everyday Life Solutions for Class 7 Science Chapter 4 Chemicals And Chemical Changes are provided here with simple step-by-step explanations. These solutions for Chemicals And Chemical Changes are extremely popular among class 7 students for Science Chemicals And Chemical Changes Solutions come handy for quickly completing your homework and preparing for exams. All questions and answers from the Science In Everyday Life Book of class 7 Science Chapter 4 are provided here for you for free. You will also love the ad-free experience on Meritnation’s Science In Everyday Life Solutions. All Science In Everyday Life Solutions for class 7 Science are prepared by experts and are 100% accurate.

Page No 62:

Question 1:

Write the symbols for the following.

1. Aluminium
2. Fluorine
3. Barium
4. Potassium
5. Iodine
6. Nickel
7. Helium
8. Hydrogen

Answer:

  1. Al
  2. F
  3. Ba
  4. K
  5. I
  6. Ni
  7. He
  8. H

Page No 62:

Question 1:

The smallest particle of a substance is called

(a) a molecule
(b) an atom
(c) an element
(d) a compound

Answer:

(b) an atom.
An atom is the smallest particle of a substance.

Page No 62:

Question 2:

Which one of the following is the symbol of an element?

(a) CO2
(b) Ca
(c) H2O
(d) HCI

Answer:

(b) Ca.
Ca is the symbol of the element calcium.

Page No 62:

Question 3:

Which one of these symbols is not that of an element?

(a) C
(b) Ca
(c) Cu
(d) CO2

Answer:

(d) CO2

CO2 is the symbol of carbon dioxide, which is compound consisting of carbon and oxygen.

Page No 62:

Question 4:

Changes, in which new substances with different properties are formed, are called

(a) physical changes
(b) chemical changes
(c) irreversible changes
(d) reversible changes

Answer:

(b) Chemical changes.

The changes which produce new substance with different properties from that of the earlier substance is called a chemical change.

Page No 62:

Question 5:

The gas which turns lime water milky is

(a) oxygen
(b) carbon dioxide
(c) hydrogen
(d) nitrogen

Answer:

(b) Carbon dioxide.
When carbon dioxide gas is made to pass through the lime water, it turns milky.

Page No 62:

Question 1:

Differentiate between an atom and a molecule.

Answer:

Atom

Molecule

An atom is the smallest particle of a substance.

When two or more atoms are joined together, they form a molecule.

Atoms may or may not exist independently.

Molecules can exist independently.

Page No 62:

Question 2:

State major differences between a compound and a mixture.

Answer:

Compounds

Mixtures

These are the substances formed due to the chemical combination of two or more elements.

These are the substances that are formed when two or more elements are mixed together without undergoing any chemical change.

Properties of the compounds differ from its constituent elements.

Mixture retains the properties of its constituent elements.

Constituents of a compound cannot be separated by physical means. Constituents of a mixture can be separated easily.

Page No 62:

Question 3:

What is valency? Give the valencies of the following: oxygen, hydrogen, sodium, magnesium, chlorine.

Answer:

Valency is the capacity of an atom to combine with the other atoms to form compounds. The valencies of the following atoms are:

  1. Oxygen (O) : 2

  2. Hydrogen (H) : 1

  3. Sodium (Na) : 1

  4. Magnesium (Mg) : 2

  5. Chlorine (Cl) : 1

Page No 62:

Question 4:

Classify the following as elements and compounds: water, nitrogen, carbon, hydrogen chloride, magnesium, aluminium oxide, calcium carbonate.

Answer:

Elements

Compounds

Nitrogen

Water

Carbon

Hydrogen chloride

Magnesium

Aluminium oxide

 

Calcium carbonate

Page No 62:

Question 5:

What are the two essential conditions for rusting? How does oiling of iron objects prevent rusting?

Answer:

Rusting of iron involves the formation of a layer of iron oxide on the surface of iron objects in the presence of moisture. Thus, for rusting to occur, water and oxygen are essential.
Oiling the surface of the iron objects protects the surface from direct contact from the atmospheric oxygen and moisture and prevents from rusting.

Page No 62:

Question 6:

Why does the cut surface of brinjal turn brown?

Answer:

When the cut surface of brinjal, comes in contact with the air, the compounds present in brinjal undergo a chemical change with the oxygen present in the atmosphere. Due to this reaction, a brown substance called melanin is produced, which turns the cut surface to brown colour.

Page No 62:

Question 7:

What are crystals? How can the crystals of sodium chloride be prepared from common salt?

Answer:

Crystals are the purest solid forms of a substance, having a natural geometric shape.
To prepare the crystals of sodium chloride, a solution containing maximum amount of common salt is dissolved in boiling water, which is then filtered to remove the insoluble impurities. This filtered solution is allowed to sit for few hours, without disturbing it. The sodium chloride accumulate to form crystals with definite geometric shapes, leaving behind the impurities in the solution.

Page No 62:

Question 1:

Match the following.

Column A Column B
Monoatomic MgO
Diatomic NaCI
Tetraatomic H2
Magnesium oxide He
Sodium chloride P4

Answer:

Column A

Column B

Monoatomic

He

Diatomic

H2

Tetra atomic

P4

Magnesium Oxide

MgO

Sodium Chloride

NaCl



Page No 63:

Question 1:

What is the difference between 2O and O2?

Answer:

The chemical symbol of oxygen is O. Here 2O simply represents that there are two oxygen atoms. O2 means the combination of two oxygen atoms. Therefore, O2 represents molecular oxygen.

Page No 63:

Question 2:

C is the symbol of carbon. What else does it represent?

Answer:

C not only represents the symbol of the carbon, but also tells the atomicity of the carbon element. Atomicity of carbon is the number of carbon atoms present in one molecule of carbon element depending on which the molecules are classified as monoatomic or diatomic or tetra atomic.

Page No 63:

Question 3:

Balance the following equations:

(a) CH4 + O2 → CO2 + H2O
(b) Na2O + H2O → NaOH
(c) Ca(OH)2 + HCI → CaCI2 + H2O
(d) Na + H2o → NaOH + H2
(e) Na + CI2 → NaCI

Answer:

  1. CH4 + 2O2 → CO2 + 2H2O
  2. Na2O + H2O → 2NaOH
  3. Ca(OH)2 + 2HCl → CaCl2 + 2H2O
  4. 2Na + 2H2O → 2NaOH + H2
  5. 2Na + Cl2 → 2NaCl

Page No 63:

Question 4:

Complete the following equations.
 

(a) Iron + Oxygen + Water → ....................
(b) Vinegar + Baking soda → ....................
(c) Carbon dioxide + Lime water → ....................
(d) Copper sulphate + Iron → ....................

Answer:

(a) Iron oxide.

(b) Carbon dioxide + Water + Other substances.

(c) Calcium carbonate + Water

(d) Iron sulphate + Copper



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