## December 1, 2014

### 10th Class Important Questions - Physical Sciences New Syllabus

Q: You are given a cylindrical vessel with a frictionless movable
piston. Water is taken in the vessel and it is heated by putting
weights on the piston.
a) How can you know when the boiling process of water started?
b) If the weights on the piston are increased what happens to the
boiling point of water?

A: a) The weights fall down when the boiling process starts.
b) There is no change in the boiling point of water, when the weights on the
piston are increased. This is because, as the piston is a frictionless
movable one, any increase in pressure in water pushes the piston
upwards.

Q: How much energy is released or absorbed when 1 gm. of water at 0°C
freezes to ice at 0°C?
A: Given: m = 1 gm.
Latent heat of fusion of ice L = 80 Cal/gm (We know)
Formula: Energy released Q = mL Cal.
Substituting the values: Q = 1 × 80 = 80 Cal.

Q: Why is slaked lime used for white washing walls?
A: A solution of slaked lime produced is used for white washing of walls.
Slaked lime (Calcium hydroxide Ca (OH)2) reacts slowly with the Carbon
dioxide in air to form a thin layer of Calcium Carbonate on the walls.
After two to three days of white washing, Calcium Carbonate formed
gives a shiny finish to the walls.

Q: Are the process of evaporation and boiling the same? (1 Mark)
A: Boiling of a liquid differs essentially from evaporation.
Evaporation takes place at any temperature while boiling occurs at a
definite temperature called the boiling point.

Q: Mention the uses of Propane, giving its formula. (1 Mark)
A: Propane is a colourless and odourless gas often used as a heating
and cooking fuel. ★ Its chemical formula is C3H8.