Chemical Analysis

because if we drew the line in pen, the pen ink would move up the paper with the solvent

After seeing how far the substance has moved and if it is pure : • measure the distance from the pencil line to the centre of the spot to see how far the substance moved • measure the distance that the solvent moved • find the Rf value by dividing the distance moved by the substance over the distance moved by the solvent

distance moved by substance / distance moved by solvent

repeating the experiment using different solvents

• several different substances may have the same Rf values • if the substance has never been analysed, then there will not be an Rf value on the database

the aqueous solution of calcium hydroxide

a substance that consists of only one element or compound

a substance that contains two or more different elements or compounds that are not chemically joined together

a substance that contains one type of atom

a substance that contains two or more types of atom chemically joined together

• a pure substance melts at a specific fixed temperature • a pure substance has a specific boiling point • impure substances melt and boil over a range of temperatures

a mixture which has been designed as a useful product, In a formulation, every chemical has been added in specific amountst. Each chemical has a specific purpose in the formulation.

• fuels • cleaning products • paints • medicines • alloys • fertilisers

to separate mixtures of soluble substances and identify substances present in the mixture, often coloured substances such as food colourings, inks, dyes

• Take a piece of chromatography paper and draw a pencil line near the bottom • Put a dot of your first colour onto the pencil line, and next to that, put a dot of your second colour • Place the piece of paper into a solvent • The solvent moved up the paper and dissolves the ink and the two coloured dots • The colour with only one spot is pure, the colour with more than one is impure

a liquid that’ll dissolve substances

the paper since it does not move

the solvent as it moves up the paper

the results of separating mixtures by chromatography

place a lighted splint into a test tube, if hydrogen is present, you’ll hear a squeaky pop sound

put a glowing splint into the mouth of a test tube, if it relights, oxygen is present

if carbon dioxide is bubbled through limewater, it turns milky or cloudy white

hold damp litmus paper into the mouth of the test tube, chlorine bleaches litmus paper and turns it white

• the colour of the flame could be hard to distinguish, especially if there is a low concentration of the metal compound • sometimes a metal compound contains a mixture of metal ions, which can mask the colour of the flame