## शनिवार, 29 जुलाई 2017

### MATTER IN OUR SURROUNDINGS PART-I

(Page No. 15)
1. What is meant by a substance?

Ans. Substance can be defined as that kind of matter where constituent particles cannot be separated from each other by any physical process since they are all similar in chemical properties.

2. List the points of differences between homogeneous and heterogeneous mixtures.

Ans.

(Page No.18)

1. Differentiate between homogeneous and heterogeneous mixtures with examples.

Ans.

2. How are sol, solution and suspension different from each other?

Ans.

3. To make a saturated solution, 36 g of sodium chloride is dissolved in 100 g of water at 293 K. Find its concentration at this temperature.

Ans. Mass of sodium chloride (solute) = 36 g

Mass of water (solvent) = 100 g

Mass of solution = 36 + 100 = 136 g

Therefore, concentration percentage = mass of solute/mass of solution

= 26.47 %

(Page No. 24)

1. How will you separate a mixture containing kerosene and petrol (difference in their boiling points is more than), which are miscible with each other?

Ans. We can separate a mixture containing kerosene and petrol by distillation technique since difference in their boiling points is more than. So through distillation we can get them separated.

2. Name the technique to separate

(i) butter from curd,

(ii) salt from sea-water,

(iii) camphor from salt.

Ans. (i) centrifugation method.

(ii) evaporation method.

(iii) sublimation method.

3. What type of mixtures are separated by the technique of crystallisation?

Ans. From impure samples of solids, pure solid crystals can be obtained by the method of crystallization for eg to obtain pure sugar from impure sample of the same.

(Page No. 24)

1. Classify the following as chemical or physical changes:

• cutting of trees,

• melting of butter in a pan,

• rusting of almirah,

• boiling of water to form steam,

• passing of electric current, through water and the water breaking down into hydrogen and oxygen gases,

• dissolving common salt in water,

• making a fruit salad with raw fruits, and

• burning of paper and wood.

Ans. cutting of trees = chemical change

melting of butter in a pan = physical change

rusting of almirah = chemical change

boiling of water to form steam = physical change

passing of electric current, through water and the water breaking down into hydrogen and oxygen gases = chemical change

dissolving common salt in water = physical change

making a fruit salad with raw fruits = physical change

burning of paper and wood = chemical change

2. Try segregating the things around you as pure substances or mixtures.

Ans. You can do it by yourself like try mixing chalk powder and water then separate them.