A. Tick the correct answer:-

1. D 2. A 3.D 4. D 5.A

B. Classify the following changes as physical or a chemical change:-

Chemical change

Burning of a magnesium.

Burning of sugar.

Wool being knitted.

Souring of milk.

Physical change

Dissolving sugar in water.

Melting of butter.

Breaking of glass bottle.

Clothes being ironed.

Drying of wet hair.

C. Give one word answer for each of the following:-

1. Oxidation 2. Crystallization 3. Iron oxide 4. Galvanizing.

D. Match column a with column b

1. Physical change 2 . Chemical change 3. Chemical change 4. Physical change.

E. Give two examples for each of the following:-

1. Elongation of rubber, melting of ice.

2. Burning of magnesium, reaction of alumina(Al₂O₃) with sodium hydroxide(NaOH).

3. Rusting of iron, tarnishing of silver container.

4. Crystallisation of impure alum, crystallisation of nitre(KNO₃).

F. Give reasons for each of the following:-

1. Iron goes into oxidation.

2. Potato contains starch which react with oxygen (atmosphere) goes into a chemical change.

G. Write true or false:-

1. False 2. False 3.False 4. False 5. False

H. Circle the odd one out:-

1. Irreversible 2. Rusting 3. Object.

I. Fill in the blanks:-

1. Physical 2. Chemical 3. Irreversible 4. Reaction 5. Chemical

J. Short answer questions:-

1. A physical change is a change of state.

2. Are chemical change is a change of constitution.

3. Rust is an oxide of iron.

4. Necessary conditions for rusting

(a) air (b) water and moisture.

5. Galvanisation is giving a layer of zinc on iron.

6. Crystallisation is cooling of warm saturated solution usually at room temperature to obtain crystals.

K. Long answer questions:-

1. Physical change

No new substance is formed.

Change of state only

e.g elongation division of rubber, dissolving salt in water.

Chemical change

A new substance is formed.

Change of composition.

e.g all chemical reaction, rusting of iron.

2. Characteristics of physical change

(1). No new substance is formed

(2). Change of state only.

(3). Physical changes affect only the physical properties of a substance such as shape, size and state.

3. Characteristics of  a chemical change

(1). New substance is formed.

(2). Change of composition.

(3). Most of the chemical changes are irreversible.

4. Iron combines with atmospheric Oxygen and moisture to form iron oxide. This is called rust. Rust is nothing but loose skin of iron oxide. This falls off from the iron surface. Thus damages iron objects.

Iron +oxygen ---->Iron oxide (rust)

5. Significance of crystallization process

(1). It gives pure substance.

(2). Have a definite and geometric crystal.

Example crystallization of epsom saltMgSO₄.7H₂O.

Sea water is collected in large number of open concrete tank from sea(CaSO₄,MgSO₄,Nacl,Cacl,Mgcl). Sunrays evaporate various salts. This solves are purified to obtained pure salt (Nacl).