IV. The boiling point is the temperature at which a substance begins to change from the liquid into the gaseous state.

II. Density

Activity 1:

Put a nail, the piece of wood, some oil & an ice cube in a beaker of water.

Ø Observation :

a. The nail sinks in the water.

b. The ice , the piece of wood & oil float on the surface of water.

Ø Conclusion:

a. The nail is denser than water, therefore it sinks.

b. The ice , candle & oil are less dense than water & therefore they float.

1 cm3 Oil Mass = 0.82g
1 cm3 Iron Mass = 7.87g
1 cm3 Water Mass = 1g


Density is calculated by the rule

Density =

Unit Mass Volume Density
g cm3 g/ cm3

A solved example:

An object’s mass is measured in the IV. The boiling point is the temperature at which a substance begins to change from the liquid into the gaseous state. lab. & found to be 50g.

The volume was also measured & found to be 25 cm3.

Can you find through calculations if this object floats or sinks in water.

Solution:

Density =

= = 2 g/ cm3

The density of this object is bigger than water 1 g/ Cm3 therefore it sinks.

Explain why:

1. Balloons filled with helium rise upwards. That’s because the density of helium is less than that of air.

2. Burning oil & flaming petroleum oil aren’t extinguished with water.

The density of oil is lower than water, therefore oil floats on top of water & keeps burning.

III. Melting point:

a. Melting is IV. The boiling point is the temperature at which a substance begins to change from the liquid into the gaseous state. the change of the state of an object from solid to liquid.

b. Melting needs heating to occur.

c. The temperature at which melting of a substance begins is called melting point.

d. Metals such as iron, copper & aluminium have high melting points.

e. Ice, wax & butter have low melting points.

Explain why:

1. Metals are molten to make machines from them.

Molten metals are easily shaped or mixed into alloys.

2. Cooking pots are made of stainless steel alloy.

Both aluminum & stainless steel have high melting points.

Stainless steel also doesn’t rust when water is heated inside IV. The boiling point is the temperature at which a substance begins to change from the liquid into the gaseous state. it.

An alloy is a mixture of 2 metals or more, metals are mixed to improve their characteristics.

Examples are :

a. Gold & copper alloy used in making jewellery.

b. Nickel chrome alloy used in making the heating coils of electric heaters & boilers.

IV. The boiling point is the temperature at which a substance begins to change from the liquid into the gaseous state.

Different substances have different boiling points.


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Документ IV. The boiling point is the temperature at which a substance begins to change from the liquid into the gaseous state.