Changing State Mixing Materials Water Cycle Heating and Cooling Separating Solids Burning Materials Evaporation

Mixing Materials When we make changes to materials by dissolving them in water or another liquid, we can sometimes reverse the change. For example, adding salt to water can be reversed by evaporation. Some materials react with a certain liquid (chemical reaction) to make a new material. For example, a new material (concrete) is made by mixing cement with water. You cannot get the cement back once it has been mixed with the water. Other solids may react with a liquid to produce a gas which escapes as bubbles. If we can change the material back it is called a reversible change, if we cannot change the material back it is called an irreversible change

Heating and Cooling Solids, liquids and gases are called the three states of matter. Materials can be changed from one state to another by heating or cooling. Water can be observed as a liquid, a solid (ice), or a gas (water vapour) and moves around the environment in a process known as the water cycle

Water-cycle The water cycle Water on the earth is constantly moving. It is recycled over and over again. This recycling process is called the water cycle. a.Water evaporates into the air The sun heats up water on land, and in rivers, lakes and seas and turns it into water vapour. The water vapour rises into the air. b. Water vapour condenses into clouds Water vapour in the air cools down and changes back into tiny drops of liquid water, forming clouds. c. Water falls as rain The clouds get heavy and water falls back to the earth in the form of rain or snow. d. Water returns to the sea Rain water runs over the land and collects in lakes or rivers, which take it back to the sea. The cycle starts all over again

Separating Solids Solids, liquids and gases have different properties. Liquids and gases can flow. Solids keep their shape. Gases can be squashed. Solids stay in one place and can be held. Solids keep their shape. They do not flow like liquids. Solids always take up the same amount of space. They do not spread out like gases. Solids can be cut or shaped. Even though they can be poured, sugar, salt and flour are all solids. Each particle of salt, for example, keeps the same shape and volume. Heating some solids can turn them into liquids. Liquids can flow or be poured easily. They are not easy to hold. Liquids change their shape depending on the container they are in. Even when liquids change their shape, they always take up the same amount of space. Their volume stays the same. Heating a liquid can turn it into a gas. Gases are often invisible. Gases do not keep their shape or always take up the same amount of space. They spread out and change their shape and volume to fill up whatever container they are in. Gases can be squashed. Heating a liquid can turn it into a gas.

Burning Materials Irreversible changes, like burning, cannot be undone. Reversible changes, like melting and dissolving, can be changed back again. Mixtures can be separated out by methods like filtering and evaporating

Evaporation water-by-evaporation By dissolving salt in water we make a solution. The salt disappears into the water. We can separate the salt from the water by boiling the solution. The water will evaporate until it is all gone. The salt will be left behind. If we collect the water vapour that evaporates we can cool it to form water again.