Elements consist of atoms of a single type, they must have the same number of protons. An example of an element is hydrogen which has one proton and no neutrons. Hydrogen is the most abundant element in the universe, which, along with the second most abundant element helium, makes up more than 95% of all normal matter.
All elements are listed in the periodic table.
Mixtures have two or more kinds of elements or compounds but are not chemically bonded. The air around us is a compound and it allows us to exchange carbon dioxide and oxygen with our lungs, which in turn drives respiration and gives us energy in the form of ATP.
Test your knowledge of elements, compounds and mixtures in one of the quizzes below.
Mixtures can be separated in one of 4 ways depending on the type of substance and its state of matter.
- Filtration and crystallisation – separating soluble and insoluble solids e.g. sand and salt
- Paper chromatography – separating soluble compounds like inks and dyes
- Simple distillation – separating solvents from dissolved salts to purify solvents like water
- Fractional distillation – separating mixtures of liquids with different boiling points e.g. hydrocarbons
How to separate salt and sand
When salt and sand have been mixed together in a beaker it is possible to separate the mixture using filtration, followed by crystallisation.
First, you will have to add water to the mixture and stir it to dissolve the water using a stirring rod. Then the salt will have dissolved and a piece of filter paper should be prepared and placed into a funnel. The funnel can then be placed into another beaker and the sand and salt solution should be carefully poured into the funnel.
The water and salt solution will slowly drain through the filter paper into the beaker. The sand will stay in the filter paper as it is insoluble and cannot fit through the holes in the paper. The sand is then known as the residue. The salt since it is soluble and dissolved in the water will go through the filter paper.
Now we have separated the sand from the salt, but now we need to separate the water from the salt. To do this we will use a different process, known as crystallisation.
It is possible to leave the beaker containing the salt and water solution until the water evaporates through evaporation. If we need the salt sooner we can use heat and boil away the water. We will need a heatproof mat, a bunsen burner, gauze, a tripod and an evaporating basin to do this.
Place the heatproof mat on a counter and then place the bunsen burner on top of it. Place the tripod over the bunsen burner and the gauze on top of the tripod.
The salt and water solution should then be poured into an evaporating basin. A beaker containing water should be placed on top of the gauze with the evaporating basin on top of the beaker. When this setup is ready the bunsen burner should be turned on to a blue flame in order to heat the beaker of water. The water in the beaker will heat the solution until the water evaporates away, leaving crystals of salt.
There is a risk of spitting from the solution when it is nearly dry so the heat should be removed before the water in the solution is fully evaporated.
Distillation involves using a still (the apparatus) to first boil liquids and then condense them and collect them in a beaker or larger tank in the case of industrial distillation for processes like making distilled water for sale and desalination to remove salt and make water potable.
Fractional distillation is a process that is able to separate similar liquids with different boiling points. The process is as follows:
- Place the mixed liquids in a boiling flask.
- Raise the temperature to the boiling point of the liquid with the lowest boiling point.
- The fractionating column serves to condense any liquid molecules which were not supposed to boil.
- The boiled liquid will condense in the condenser and drip into the collection beaker.
- Raise the temperature to the boiling point of the next liquid and repeat.
Test your knowledge of separating mixtures in one of the quizzes below.