GCSE OCR Gateway Science C2

A colloid is a mixture of tiny particles of one thing mixed in another.

In the case of paint it is a mixture of the pigment particles in the binding agent. The solid particles are not dissolved they are simply suspended in the oil. The particles stay like this because they are very small. Only paint which has been left for a very long time and not stirred will settle out.

There are two types of paint : oil based ones which we more commonly call GLOSS PAINTS and ones with less solvent and water based paints which we called EMULSION PAINTS.

WHAT HAPPENS AS AN OIL BASED PAINT DRIES

1. Apply paint to a surface.

2. The solvent in the paint is volatile and easily evaporates in to the air.

3. The binding agent and pigment particles remain on the surface.

4. The oxygen in the air reacts with the oil to form a skin which remains stuck to the surface.

The crust is 'cracked' into huge pieces called tectonic plates. Oceanic plates lie beneath the oceans and continental plates form the continents. The tectonic plates are less dense than the mantle and float on top of it.

Convection Currents in the mantle transfer energy to the plates, causing them to move very slowly.

In a volcano the magma is forces out onto the surface of the Earth as a stream of lava.

The lava cools quickly to form igneous rock with small crystals.

When magma is forced up through cracks in the crust but does not reach as far as the surface, it cools more slowly. This forms igneous rocks with large crystals.

Iron rich magma, which is runny and gives lava that runs slowly from the volcano, forms basalt. Silica-rich magma, which gives lava that is ejected explosively, forms rhyolite.

Electrolysis

Impure copper can be purified in the laboratory using an electrolysis cell.

In an electrolysis cell the anode is impure copper. The anode dissolves into the electrolyte and pure copper coats the cathode. The cathode is 'plated' with new copper.

An alloy is a mixture of two elements, at least one of which is a metal.

ALLOY-------------------MAIN METAL-----------------------USE--------------------------------------------------

amalgam----------------mercury-------------------------------tooth fillings----------------------------------------

brass---------------------copper and zinc--------------------hinges, screws, ornaments------------------

solder--------------------lead and tin--------------------------joining wires and water pipes----------------

Rusting

iron + water + oxygen → hydrated iron(III) oxide

Materials used to make Cars

Each part of the car is made from a material that has properties that make it suitable for use in that part of the car. For example:

• the body is made of steel becuase it is strong and can be shaped easily
• seat covering are made of fibres because they are flexible and hardwearing, but it is strengthened by fibres or steel mesh
• the windscreen is made of glass because it is transparetn and scratch resistant.

Common Air Pollutants

Carbon monoxide - incomplete combustion of petrol or diesel in car engines

Oxides of nitrogen - in car engines from the reaction of nitrogen and oxygen

Sulfur dioxide - combustion of fossil fuels containing sulfur, for example, coal

Catalytic converters

Car exhaust systems have catalytic converters. These convert carbon monoxide into carbon dioxide:

carbon monoxide + nitrogen oxide → nitrogen + carbon dioxide

2CO + 2NO → N₂ + 2CO₂