Chem paper2

REQUIRED PRACTICAL 6 - Determine the colours present in an unknown mixture of food colouring using chromatography - possible method

1. Use a ruler to draw a horizontal pencil line 2 cm from a short edge of the chromatography paper.

Mark five pencil spots at equal intervals across the line. Keep at least 1 cm away from each end.

2. Use a glass capillary tube to put a small spot of each of the known colourings on four of the pencil spots. Then use the glass capillary tube to put a small spot of the unknown mixture on the 5th pencil spot.

Try to make sure each spot is no more than 5 mm in diameter.

Label each spot in pencil.

3. Pour water into the beaker to a depth of no more than 1 cm.

4. Tape the edge of the chromatography paper to the glass rod. The paper needs to be taped at the end furthest from the spots.

Rest the rod on the top edge of the beaker. The bottom edge of the paper should dip into the water.

Ensure that the:

• Pencil line is above the water surface

• Sides of the paper do not touch the

beaker wall

5. Wait for the water solvent to travel at least three quarters of the way up the paper. Do not disturb the beaker during this time.

Carefully remove the paper. Draw another pencil line on the dry part of the paper as close to the wet edge as possible.

6. Hang the paper up to dry thoroughly.

7. Measure the distance in mm between the two pencil lines. This is the distance travelled by the water solvent.

8. For each of the four known colours, measure the distance in mm from the bottom line to the centre of each spot.

9. Determine the Rf value for each substance.

10. Match the Rf value of the spots from the unknown mixture with the known values of the other colourings to determine which of them are present and if any unknown substances are present.

REQUIRED PRACTICAL 6 - Determine the colours present in an unknown mixture of food colouring using chromatography - risk assessment

• Safety goggles should be worn throughout

REQUIRED PRACTICAL 7 - Testing for ions - Method for a carbonate test

1. Pour around 1 cm depth of each of the labelled sodium solutions (sodium salts containing carbonate) into five test tubes in the rack.

2. Place 2 cm depth of limewater in a sixth test tube.

3. Add 1 cm depth of dilute hydrochloric acid to each sodium salt in turn.

Only if you see bubbles, quickly use the teat pipette to transfer the gas produced to the limewater. Your teacher may show you how to do this.

You will need to take several pipettes of the gas to get a change in the limewater.

4. Record your results.

5. Empty and clean the test tubes.

REQUIRED PRACTICAL 7 - Testing for ions - Method for a flame test

1. Pour around 1 cm depth of each of the labelled chloride solutions into five test tubes in the rack. (Chloride solutions of lithium, sodium, potassium, calcium and copper).

2. Dip the nichrome wire into the first solution. Then hold the tip of the wire in a blue Bunsen burner flame.

3. Record your observations.

4. Clean the wire carefully.

5. Repeat steps 2‒4 for each of the other four solutions.

6. Empty and clean the test tubes.

REQUIRED PRACTICAL 7 - Testing for ions - Method for a halide test

1. Pour around 1 cm depth of each of the labelled sodium solutions (sodium salts containing chloride, bromide and iodide) into five test tubes in the rack.

2. Add a few drops of dilute nitric acid to each solution. Then add 1 cm depth of silver nitrate solution.

3. Record your observations.

REQUIRED PRACTICAL 7 - Testing for ions - Method for a sulfate test

1. Pour around 1 cm depth of each of the labelled sodium solutions (sodium salts containing sulfate) into five test tubes in the rack.

2. Add a few drops of dilute hydrochloric acid to each solution. Then add 1 cm depth of barium chloride solution.

3. Record your observations.

4. Empty and clean the test tubes.

REQUIRED PRACTICAL 7 - Testing for ions - Method for determining an unknown ion

1. Repeat the flame, carbonate, sulfate and halide tests on the unknown salt solution.

2. Compare to your previous results to determine the substance.

REQUIRED PRACTICAL 7 - Testing for ions - risk assessment

• Safety goggles should be worn throughout

• Some of the substances are irritants and harmful (e.g. barium chloride solution)

Activation energy

This is the minimum energy required for a reaction to take place.

Addition polymerisation

Alkenes can be used to make polymers such as poly(ethene) and poly(propene) by addition polymerisation. In addition polymerisation reactions, many small molecules (monomers) join together to form large molecules (polymers). The repeating unit has the same atoms as the monomer because no other molecule is formed in the reaction. To name the polymer, it is just the alkene in brackets with poly in front e.g. poly(butene).

Addition reactions of alkenes

Alkenes can react with:

• Hydrogen

• Water

• Halogens

Advantages of instrumental methods over practical methods

They are a faster and more accurate/sensitive method of detecting and identifying elements and compounds

Alcohols

• A homologous series of hydrocarbons

• They have an -OH bond, which is their functional group

• This -OH must be represented when writing out the formula, and is usually kept at the end

Alkanes

• These are saturated, meaning there are only single bonds between atoms

• They are relatively unreactive, although they do combust

• Their single bonds are quite strong

• They are a homologous series of hydrocarbons (organic compounds with the same functional group and similar chemical properties)

• There are trends in their physical properties

Alkenes

• A homologous series of hydrocarbons

• They have a double carbon (C=C) bond, which is their functional group

• They are unsaturated because they have two fewer hydrogen atoms than the alkane with the same number of carbon

• They are more reactive than alkanes

Alternative methods of extracting copper

• Phytomining

• Bioleaching

Aluminium additional information

Aluminium is naturally low in density and is used for aluminium foil. It naturally forms a layer of aluminium oxide in air, which makes it resistant to corrosion.

Amino acids

An amino acid contains two different functional groups: a basic amino group (NH₂) and a carboxyl group (COOH), e.g. glycine, the smallest amino acid.

Amino acids can form polypeptides via condensation polymerisation. The amino acid group can react with the acid group of another (continuously) forming a polymer chain. For every new bond formed another water molecule is lost.

Atmospheric pollutants that come from combustion of fuels

• Carbon dioxide

• Water vapour

• Carbon monoxide

• Sulfur dioxide

• Oxides of nitrogen

Bioleaching

This uses bacteria which convert copper compounds into soluble copper compounds. This produces a leachate (the solution made by the process) that contain metal compounds.

Carboxylic acid and water

They dissolve to form acidic solutions.