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**(i) Temperature**

When the temperature of a substance is increased, it expands hence increasing its volume. The density then decreases.

When the temperature of a substance is reduced, it contracts hence reducing its volume. The density then increases.

**(ii) Pressure**

Pressure only affects the density of gases.

When the pressure of a given mass of a gas is increased, the gas molecules become squeezed and occupy a smaller volume. This increases the density of the gas.

When the pressure of a given mass of a gas is reduced, the gas molecules become occupy a larger volume. This decreases the density of the gas.

**Uses of** **density**

It is used to: -Identify materials for construction

-Test the purity of a substance

-Choose the light gases to fill balloons

**Example 1:**

A Perspex box has a10cm square base containing water to a height of10 cm. A piece of rock of mass 600g is lowered into the water and the level rises to 12 cm.

(a) What is the volume of water displaced by the rock?

V = L x w x h

= 10 x10 x (12-10)

= 200 cm3

(b) What is the volume of the rock?

Volume of rock = volume of water displaced

= 200cm3

**Alternatively,**

Volume of water before adding the rock

V1 = L x W x H

= (10cm x 10cm x 10cm)

= 1000cm3

Volume of water after adding the rock

V2 = L x W x H = (10 x 10 x 12) cm3 = 1200cm3

Volume of water displaced V= V2 – V = (1200 – 1000) cm3

= 200cm3

(c) Calculate the density of the rock

**Example 2:**

(ii) The mass of 24.4cm3 of mercury is 332g. Find the density of mercury.(=13.6 gcm-3)

(iii) An 800g solid measures 10cm by 5cm by 4cm. Determine its density.(= 4 gcm-3)

(iv) A glass stopper of volume 16cm3 weighs 40g. Calculate its density in :

(i) gcm-3 .(=2.5 gcm-3)

(ii) kgm-3. (=2500kgm-3)

(v) The density of copper is 8.9gcm-3. What is the mass of 100cm3 of copper? .(=890 g)

(vi) When a piece of irregular stone of mass200g is lowered in a measuring cylinder, the initial and final volumes were 500cm3 and 600cm3 respectively. Calculate the density of the stone.(=2gcm-3)

(vii) An empty beaker weighs 120g in air and 180g when filled with 75cm3 of methylated spirit. Find the density of methylated spirit. (=0.8gcm-3)

(viii) What is the mass of 1.5litres of water? (= 1.5kg)

- The oil level in a burette is 25cm3.50 drops of oil fall from a burette. If the volume of one drop is 0.1cm3.What is the final oil level in the burette. [30cm3]

3. A measuring cylinder has water level of 13cm.What will be the new water level if 1.6g of a metallic block of density 0.8g/cm3 is added.

- A perspex box having 6cm square base contains water to a height of 10cm.

(a) Find the volume of water in the box [360cm3]

(i) Find the new volume of water? [468cm3]

(ii) Find the volume of the stone? [108 cm3]

(iii) Find the density of the stone. [25 g/cm3]

A steel C.P.U below, has a mass of 560g

Find its density

(i) in g/cm3

(ii) in kg/m3

- 200g of liquid Y of density 4gcm-3. Calculate the density of the mixture.
- Liquids X and Yare mixed to form a solution. If the density of X is 0.8gcm-3 and volume is 100cm3, density of Y 1.5cm-3 and its volume is 300m3.Find the;

(i) mass of liquid X [80g]

(ii) mass of liquid Y [450g]

(iii) Density of a mixture [1.325gcm-3]

- In an experiment to determine the density of a pin, 100pins are gently lowered into a measuring cylinder containing 12cm3 of water. The water in the cylinder rose to 98cm3. Find the;

(i) volume of a pin.

(ii) density of the pin in kgm-3