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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:
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.
Density =
A solved example: An object’s mass is measured in the 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.
= = 2 g/ cm3
The density of this object is bigger than water 1 g/ Cm3 therefore it sinks.
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 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. f. Metals have high melting points. Explain why: 1. Metals are molten to make machines from them.
2. Cooking pots are made of stainless steel alloy. Bec. Both aluminum & stainless steel are good conductor of heat and have high melting points.Stainless steel also doesn’t rust when water is heated inside it.
An alloy is a mixture of 2 metals or more, metals are mixed to improve their characteristics.
a. Gold & copper alloy used in making jewellery. b. 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. Date: 2015-12-24; view: 1204
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Put a nail, the piece of wood, some oil & an ice cube in a beaker of water.
Density is calculated by the rule
Solution:
Density =
Explain why:
Bec. Molten metals are easily shaped or mixed into alloys.
Examples are :
Nickel chrome alloy used in making the heating coils of electric heaters & boilers.