UNIT 6. MATTER (NATURAL SCIENCE)

UNIT 6. MATTER

PHYSICAL CHANGES

·         Change in state

Water can ba in three states: solid, liquid and gas.  The atoms of water behave differently in each state:

-          In a solid state atoms are packed together and move very little.

-          I a liquid state, atoms are close but they move more.

-          In a gas state, atoms are far and move quickly in all directions.

·         Change in shape

Matter can change its shape but the chemica composition can be the same. Forexample, when we cut a piece of Wood.

·         Change of position or texture

Matter can change its position and texture without chaning its properties.

·         Types of physical changes

Physical changes can be reversible or irreversible.

-          Reversible: matter can be undone and done again.

-          Irreversible: are permanent.

·         Mass, volumen and density

-          Mass is the amount of matter in an object. We measure mass in grams (g) and kilograms (kg) and we use scales.

-          Volume is the space an object occupies.  We measure volumen in mililitres (ml) and litres (l).

-          Density is calculated by dividing the mass of an object by its volume.  It is expressed as grams per mililitre (g/ml) or kilograms per litre (kg/l).

CHEMICAL CHANGES

                Chemical reactions change the properties of the original substance and a new substance is created.  Combustion, oxidation and fermentation are irreversible changes.

·         Combustion

Combustion is a chemical reaction that produces ernergy in the form of heat and light.  It happens when the oxygen reacts with a fuel like gas or oil. When they burn, the atoms  react and form new substances like smoke.

·         Oxidation

Some metals and food (for example, apples and potatoes) react when they are in contact with air.  Atoms are changed into a new substance that has a brown color and is called rust. This process is called oxidation.

·         Fermentation

Fermentation is a chemical reaction in which fungi and bacteria change organic substances into other substances. In the process of fermentation fungi produce alcochol and bacteria produce lactic acid. Fermentation is used to make some food (cheese or bread) and drink (wine) and to preserve food.

SEPARATING MIXTURES

There are two types of mixtures:

-          Heterogeneus mixtures: we distinguish the components of the mixtures and they can be separated easily.

-          Homogeneus mixtures: we do not distinguish the components but we can separate them.

We can separate  mixtures in different ways:

-          Magnetic separation: magnets attract metal. We use this separation when we want to separate mixtures with substances that are attracted by metals and other substances that are not.

-          Decantation: heavy sediments sink to the bottom of the container. When we decant a liquid, we pour off the liquid and and the sediments stay in the container.  We can also use decantation to separate two liquids of different density. The liquid with higher density goes down and the other liquid goes up.

-          Filtration: separates smaller particles from a liquid or gas using a filter.

-          Evaporation: it is used to separate solids that are disolved in water. Using heat, liquid transforms into vapour and the solids can be collected. (For example, to separate sand from water).

-          Distillation: it is used when two liquids evaporate at different rate. For example, ethanol has a lower boiling point than water. It evaporates and forms vapour. This vapour is cooled resulting in pure ethanol. For example, it is used to produce alcohol and in the petrochemical industry.