Matter-Nature and its Behaviour (Long Answer Type Questions)

Question 1. Classify the following as physical change or chemical change.

(i) Burning of magnesium ribbon in air

(ii) Burning of sulphur in air

(iii) Electrolysis of water

(iv) Purification of copper sulphate from impure copper sulphate by crystallization,

(v) Preparation of sugar solution

(vi) Conversion of milk into curd

(vii) Evaporation of alcohol

(viii) Burning of coal Ans.

Answer.

(i) Chemical change (oxide of magnesium is formed)

(ii) Chemical change (oxide of sulphur formed)

(iii) Chemical change (hydrogen and oxygen formed)

(iv) Physical change (no new substance formed)

(v) Physical change

(vi) Chemical change

(vii) Physical change

(viii) Chemical change (carbon dioxide formed)

Question 2. Differentiate between True solution, Colloidal Solution, and suspension with respect to there properties in tabular form.

Answer.

Property	True solution	Colloidal Solution	Suspension
1. Appearance	They are clear and trans parent	Thy are translucent	They are opaque.
2. Visibility	These particles are visible	Scattering of light by particle is observed under ultra-microscope.	Particles are visible to naked eye.
3. Particle size	It is less than 1 nm (nanometer)	It is between 1 nm and 100 nm.	Particles size is more than 100 n .m.
4. Diffusion	They diffuse quickly	They diffuse slowly	They do not diffuse.
5. Setting	They do not settle	They do not settle	They settle on standing
6. Filterability	They can pass through ordinary filter paper as well as animal membrane.	They pass through filter paper but not through animal membrane.	They do not pass through filter paper or membrane.

Question 3. Suggest a scheme for the separation of constituents of the following mixture: Sulphur + sand + sugar + iron filings

Answer.

 A magnet is moved several times over the mixture : containing sulphur, sand, sugar and iron filings. The iron filings are attracted by the magnet, they stick to the magnet and get separated.

The remaining mixture of sugar, sulphur and sand is stirred with water when sugar dissolves in it. On filtration sugar solution is obtained as a filtrate from which sugar can be recovered by evaporation. The residue contains sulphur and sand.

Sulphur and sand mixture is shaken with carbon disulphide when sulphur dissolves in it but sand remains undissolved. On filtration, sulphur is obtained as a filtrate from which solid sulphur can be recovered by evaporating carbon disulphide. Sand is left behind as a residue on the filter paper.