C4.2 - Identifying The Products Of Chemical Reactions

• You can test for carbon dioxide using limewater (calcium hydroxide solution). • Limewater turns cloudy white when carbon dioxide is bubbled through it. • The change is caused by calcium hydroxide reacting with carbon dioxide to form water and a white precipitate of calcium carbonate.

• Chlorine dissolves in water to form an acidic solution. • Chlorine bleaches dyes. • Use a drop of tap water to dampen a piece of blue litmus paper. • Hold the paper near to a container that holds the substance. • If chlorine is present, the paper turns red then white.

• With the container well away from your nose, breathe in enough air to almost fill your lungs. • Hold the container a few centimetres away from your nose, and waft any smell towards you. • Take a cautious sniff.

Hydrogen - Place a lighted splint near the mouth of the container of gas - If hydrogen is present, a squeaky pop noise will occur. Oxygen - Place a glowing splint near the mouth of the container of gas - If oxygen is present, the splint should relight.

• Metal ions are heated, energy is transferred to their electrons. • This makes their electrons move into higher electron shells. • When the electrons move back to their normal electron shells, energy is transferred to the surroundings as radiation, which you see as light.

• Clean a wire loop attached to a handle several times by dipping it into hydrochloric acid, then rinsing it with distilled water. • Once it is clean, there will be no change in the colour of the Bunsen burner flame when you hold the loop in it. • Dip the clean loop into the test powder or solution. • Use the handle to hold the loop in the edge of a roaring blue flame. • Record the flame colour.

• To ensure it is not contaminated with the previous sample. • So you will not confuse flame colours or mix them.

• Lithium - Li+ - Red • Sodium - Na+ - Yellow • Potassium - K+ - Lilac • Calcium - Ca2+ - Orange/Red • Copper - Cu2+ - Green/Blue

• Different metals produce different coloured precipitates. • Add a few drops of sodium hydroxide solution to a solution containing metal ions. • Note the colour of any precipitate formed.

Iron(II) - Green Iron(III) - Orange/Brown Copper(II) - Brown Calcium - White Zinc - White

• Add excess sodium hydroxide solution. • Zinc hydroxide dissolves to form a colourless solution. • Calcium hydroxide does not dissolve.

• Add a few drops of hydrochloric acid. • Then add a few drops of barium chloride solution. • If sulphate ions are present you would get a white precipitate of barium sulphate.

• Hydrogen ions from dilute acids react with carbonate ions to produce carbon dioxide and water. • Add a few drop of hydrochloric acid. • If carbonate ions are present, bubbles of gas will be produced. • You can confirm the gas is carbon dioxide by bubbling it through limewater.

• Add a few drops of nitric acid. • Then add a few drops of silver nitrate solution. • Chloride ions - Silver chloride - White • Bromide ions - Silver bromide - Cream • Iodide ions - Silver iodide - Yellow

Silver fluoride is soluble in water.

• It works whether the carbonate compound is in the solid state or in a solution. • This is useful because most carbonates are insoluble.

Ba2+ (aq) + SO42- (aq) -> BaSO4 (S) 2H+ (aq) + CO32- (aq) -> CO2 (g) + H2O (l)

A technique for analysing a substance that depends upon a machine.

• Sensitivity - Instruments can analyse very small amounts of substances. Useful if the substance is difficult or expensive to obtain. • Accuracy - Instruments are very accurate. Can be calibrated using internationally accepted standards. • Speed - Instruments can carry out analysis quickly and they can run all the time.

• A gas chromatogram is a chart that represents the different substances in a mixture. • Each peak represents a substance present in the mixture. • The areas under each peak show the relative amount of each substance in the mixture. • The retention time, the time taken for each substance to travel through the chromatography column, is different for different substances.

• A machine that can measure masses of atoms and molecules. • Used to analyse the relative amounts of different isotopes of an element and the structure of molecules.

1) Ionisation - Atoms bombarded with electrons. - The electrons collide with the atoms to give a 1+ charge which makes the fragments unstable. 2) Acceleration - All the fragments are made to have the same KE. 3) Deflection - The fragments are passed through a magnetic field and deflect proportionate to their mass and charge. 4) Detection - The beams of fragments are detection electronically. - It detects how much of the mass is deflected and whether the sample is a pure substance.

• Relative abundance against the mass to charge ratio. • Each peak represents a fragment of the molecule. • The peak on the far right represents the molecular ion. • The mass to charge ratio of the molecular ion peak is equal to the relative formula mass, Mr, of the molecule.