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VI.Thermal conduction
| Good thermal conductors | Bad thermal conductors | |
| Definition | They allow heat to pass through them. | They dont allow heat to pass through them. |
| Examples | Metals such as copper, aluminium & iron. | Wood & plastic. |
| Uses | Aluminum is used in making cooking pots. | Wood & plastic are used in making handles of cooking pots. |
VII. Rusting of metals:
When different metals are exposed to humid air for some time, some of them rust , others dont rust.
| The ability of the metal to react with oxygen(rust) in the presence of water | High (active) | Low (inactive) |
| Examples | Sodium Potassium | Gold, silver platinum |
| Uses |  Making jewellery
|
Explain why:
Metallic parts of bridges, cars & light posts are painted periodically.
Painting prevents the reaction between the metal & oxygen & protects them against rust.
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I. Complete the following statements:
1. The unit of mass is .while the unit of volume is .
2. Density is the .of a unit volume of a substance & its unit is .
3. Some examples of good electric conductors are .& .
4. 
.doesnt conduct heat or electricity.
II. Explain why:
1. A piece of lead sinks in a basin of water while a piece of wood floats on the surface.
.
2. A piece of ice which left at room temperature becomes water.
3. Metallic parts of bridges & light posts can stand for long time without rust.
III. Problems :
1. In the lab , the mass of a piece of iron was measured to be 87 g. When the piece was immersed in a graduated cylinder that contains 90 cm3 , water level increased up to 100 cm3. Calculate the density of iron.
2. The mass of an object is 8g. its density = 0.5 g/ cm3 . calculate the volume of the object.
IV. Whats meant by:
1. Matter
.
2. Melting point
..
3. Electric conductivity
V. Write the scientific term:
| 1. The temperature at which a substance changes from the liquid state to the gaseous state. | |
| 2. Substances which dont allow heat to pass through them. |
open a bottle of perfume the smell of the perfume spreads in the room indicating that the perfume consists of tiny particles called molecules . they have the smell of the perfume & spread in the air.
Activity 1:
With a dropper , put a drop of liquid colour in a beaker of water.
Ø Observation:
The colour spreads in the water
Ø Conclusion :
Molecules are in continuous motion.
Activity 2:
Measure 50 ml of water with a graduated cylinder.
Measure 50 ml of vinegar then pour it in the cylinder that contains water..
Ø Observation:
The volume of water & vinegar is less than 100 ml.
Ø Conclusion :
Some vinegar molecules occupy the spaces between water molecules.
Matter consists of molecules. The spaces between the molecules are called intermolecular spaces .
Attraction forces keep molecules together .
Comparison between the 3 states of matter.
| Points of comparison | Solid state | Liquid state | Gaseous state |
| Volume | Definite | Definite | Not Definite |
| Shape | Definite | Not Definite, they take the shape of their containers | |
| Examples | Ice , iron , aluminiumm. | Water, alcohol, oil | Water vapour , oxygen , carbon dioxide |
| intermolecular forces | Very strong | Weak | Dont exist |
| intermolecular spaces | Tiny | Bigger | Very large |
| Motion of molecules | Limited | More free | Completely free |
Explain why:
Date: 2015-12-24; view: 1922
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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. | | | A molecule consists of atoms. |