Science - chemistry

Dissolving

dissolving is one way to mix mixtures.

Chromatography

paper chromatography is a method for separating dissolved substances from one another.

Mixtures

- A mixture contains different substances that are not chemically joined to each other. - A mixture of iron filings and sulfur powder can easily be separated using a magnet. The iron filings are attracted to the magnet but the sulfur powder is not.

What is carbon?

- Carbon is a non-metal element and is solid at room temperature. - Carbon exists in different forms, including graphite, diamond and graphene. - Depending on its form carbon has different properties.

what are elements?

- An element is a substance that cannot be broken down into any other substance. - Every element is made up of its own type of atom. - Everything in the universe contains the atoms of at least one or more elements. - The periodic table lists all the known elements and groups together those with similar properties. - Most elements are metals, which are shiny and conduct electricity well. - Metals include gold, aluminium and iron which are all solid at room temperature. Mercury is the only metal that is liquid at room temperature. - Some elements are non-metals. Most non-metals are gases at room temperature and do not conduct electricity. -Non-metal elements with these properties include oxygen, hydrogen and chlorine. A few non-metals, such as carbon and sulphur, are in a solid state at room temperature.

What is nitrogen?

- Nitrogen is an element. It's a gas at room temperature. - Nitrogen makes up about 78% of the Earth's atmosphere. - Liquid nitrogen is very cold, so it is often used to freeze food.

What is oxygen?

- Oxygen is a non-metal element that is a gas at room temperature. Its molecules contain two oxygen atoms. - Oxygen is vital for respiration, which is the process that transfers energy from glucose to cells. - Oxygen is necessary for burning to occur. However, burning will only happen when the mixture of fuel and oxygen is hot enough.

Compounds

A compound is a substance that contains atoms of two or more different elements, and these atoms are chemically joined together. For example, water is a compound of hydrogen and oxygen. Each of its molecules contains two hydrogen atoms and one oxygen atom. There are very many different compounds.

Different forms of carbon

Diamond: - Diamond is used in jewellery because it will sparkle and reflect light in an attractive way. Diamond's hardness and high melting point make it useful for cutting tools, such as the diamond-tipped discs used to cut bricks and concrete. Graphite: - The carbon atoms in graphite are arranged in layers that slide over each other. This makes graphite slippery. It is sometimes used instead of oil to lubricate locks. Graphite is the only non-metal element that conducts electricity. Graphene: - Graphene is a recently discovered material. It has been found to be 300 times stronger than steel and much harder than diamonds. Unlike graphite, graphene only contains a single layer of carbon atoms. - Scientists are still working out how we could use it, but in the future it could be used to make better gloves, sportswear and medical devices.

Diffusion

Diffusion is another way to make a mixture. Particles of different substances mix together during diffusion. This happens: • quickly in gases, because their particles are able to move quickly in all directions • slowly in liquids, because their particles can move around each other, and they can push other particles around • not at all in solids because their particles can only vibrate on the spot

Chemical symbols

Each element is given its own chemical symbol, like H for hydrogen or O for oxygen. Chemical symbols are usually one or two letters long. Every chemical symbol starts with a capital letter, with the second letter written in lower case.

Evapouration

Evaporation is used to separate a soluble solid from a liquid. For example, copper sulfate is soluble in water - its crystals dissolve in water to form copper sulfate solution. During evaporation, the water evaporates away leaving solid copper sulfate crystals behind.

atoms

Everything is made from atoms, including you. Atoms are tiny particles that are far too small to see, even with a microscope. If people were the same size as atoms, the entire population of the world would fit into a box about a thousandth of a millimetre across.

fractional distillation

Fractional distillation is a method for separating a liquid from a mixture of two or more liquids.

What is hydrogen?

Hydrogen is an element; it exists naturally as a molecule. Each hydrogen molecule is made up of two hydrogen atoms. In petrol and diesel cars, the burning of fuel produces carbon dioxide and water. Extra carbon dioxide in the air promotes global warming. In hydrogen cars hydrogen reacts with oxygen in a fuel cell, making electricity to run the car. The only waste product of this process is water vapour.

filtration

If a substance does not dissolve in a solvent, we say that it is insoluble. For example, sand does not dissolve in water - it is insoluble. Filtration is a method for separating an insoluble solid from a liquid. When a mixture of sand and water is filtered: • the sand stays behind in the filter paper (it becomes the residue) • the water passes through the filter paper (it becomes the filtrate)

Pure chemical substances

In science, a pure substance contains only one element or compound.

How is nitrogen used?

Nitrogen has just one type of atom, so it is an element. It's found naturally as a molecule, each containing two nitrogen atoms. This gives it a chemical formula of N₂. Nitrogen has a low melting and boiling point and is a gas at room temperature. The Earth's atmosphere is made up of 78% nitrogen. The next most common gas is oxygen, at 21%. Nitrogen isn't very reactive, but it can react with oxygen at high temperatures, such as in car engines. These reactions make nitrogen oxides. The boiling point of nitrogen is −196 °C, so liquid nitrogen is very cold indeed. This means liquid nitrogen is ideal for freezing food, such as vegetables, very quickly, allowing them to stay fresher for longer.

How is oxygen useful?

Oxygen is a non-metal element and is found naturally as a molecule. Each molecule is made up of two oxygen atoms that are strongly joined together. Oxygen has low melting and boiling points, so it is in a gas state at room temperature.

simple distillation

Simple distillation is a method for separating the solvent from a solution.

Elements

There are over a hundred different elements. The atoms in a particular element are the same as each other, and they are different from the atoms of all other elements. For example, lead and gold are elements. A piece of pure gold contains only gold atoms. A piece of pure lead contains only lead atoms. The atoms of some elements do not join together, but instead they stay as separate atoms. Helium is like this. The atoms of other elements, such as hydrogen and oxygen, join together to make molecules.

more uses of oxygen

When animals breathe in, oxygen molecules enter the lungs and pass through the lung walls into the blood. The blood carries oxygen to the cells of the body, where it takes part in a chemical reaction with glucose. This chemical reaction is called respiration. Respiration happens all the time in every living thing: it is how the cells receive energy. If an animal or plant does not have enough oxygen, it will not be able to respire and will die. Burning If the temperature is high enough, many substances will burn in oxygen. When a substance burns, it reacts with oxygen: this happens in wood fires and also in car engines, which burn petrol. The chemical reaction transfers energy in order to make the engine work. The scientific word for burning is combustion.

Compounds

a compound contains atoms of different elements, chemically joined together.