Elements, Compounds and Mixtures

• A pure substance made up from the same type of atom (same number of protons) • Examples: O and Mg₂ If there is only one atom in the substance, than it is just an atom, if it has more than one bonded together, it is a molecule. In this case, both are elements.

• A pure substance made up of two or more different elements bonded together, which cannot be seperated by physical means • Examples: NH₄ and MgO A compound must have different elements, if it is the same element bonded together than it is a molecule (although molecules can have different elements too).

• A combination of two or more substance (elements or compounds) which are not bonded together and can be seperated by phsyical means • Examples: Air

• A substance which only contains one kind of compound or element If anything else is added, it becomes a mixture

As long as it is the same pure mixture, it will always be the same

Unfixed as each substance will have a different melting/boiling point inside of the mixture, broadening its range

• Slowly heat a substance, and compare its melting/boiling point to data books • The closer it is to the value, the purer the substance is

A liquid from a soluble solid (that has dissolved to form a solution) Important: This process is more favourable for obtaining the liquid, while crystallisation is more favourable for obtaining the solute

• The solution is heated, and the liquid will evaporate, producing a vapour which rises and is filtered into a vapour condenser • In the condenser, the vapour condenses and turns into the pure version of the liquid which is collected in a beaker • The pure solute will be left behind The condenser just cools the vapour to its condensation point, and it does this by having a constant stream of water running through it

Two or more liquids with different boiling points from a mixture

• The solution is heated to the temperature of the liquid with the lowest boiling point, which evaporates and produces a vapour which rises and is filtered into a vapour condenser • It will then condense and the pure version of this liquid will be collected in a beaker • If there are more than two liquids to seperate, you can repeat this with the liquid that has the 2nd lowest boiling point and so on, collecting each liquid in a different beaker • Once done you will be left with the pure and unmixed versions of the liquids

A liquid from an insoluble solid (which has not dissolved)

• A piece of filter paper is placed in a funnel above a beaker • The mixture of the insoluble solid and the liquid are poured onto the filter paper • The small liquid particles will pass through the filter paper as a filtrate, leaving the larger insoluble solid molecules behind

A soluble, dissolved solid from a liquid (in a solution)

• The solution is heated, evaporating the solvent which increases the concentration of solute, leading to it becoming a saturated solution • The saturated solution is left to cool, and crystals of the solute will begin to form due to decreasing solubility (caused by the temperature drop) • Seperate the crystals and the remaining solvent/solution by decanting • Wash them with water and leave them to dry in a warm place • The new crystals only form because the solution is saturated - which is the why the solvent is evaporated at the start to form the saturated solution • On top of that, the reason why the solute is dissolved at the starting temperature before the experiment is because there is enough solvent so the solution is not saturated

Different soluble substances that have a different solubility in a mixture

• Draw a pencil line on the chromatography paper, and place spots of the different samples across it • Lower the paper into solvent, but make sure the pencil line sits above the solvent so the samples do not dissolve into the solvent (stationary phase) • The solvent will travel up the paper by capillary action, taking some of the samples with it (mobile phase) • The parts of the samples with a higher solubility will travel further up the paper than the parts with a lower solubility

There will only be one spot

There will be multiple spots up the chromatogram, the distance travelled of each depending on solubility

The line at the top of the solvent indicating how far the solvent has travelled

Distance travelled by substance/distance travelled by solvent • The value will always be between 0-1, higher meaning higher solubility • The distances travelled are always between the baseline (pencil line) and the substance/solvent front respectively

Comparing the Rf value of an unknown substance to that of a known substance to identify the substance