required practicals

Question 1

Describe a practical to separate an insoluble solid from a liquid.

Answer 1

insoluble solid from liquid:
FILTRATION
1) place filter paper in funnel
2) pour mixture in with beaker underneath
- liquid will pass into beaker, sold will collect in filter paper

Question 2

Describe a practical to separate a soluble solid from a liquid.

Answer 2

soluble solid from liquid:
CRYSTALLISATION
1) put liquid in beaker
2) heat until just boiling
3) add solid and stop when it no longer dissolves
4) heat in evaporating basin until crystallisation point and then for 48 hours to cool
5) scrape out crystals, filter excess and gently dry

Question 3

Describe a practical to separate a soluble solid from a liquid and want to keep the liquid.

Answer 3

soluble solid from liquid:
SIMPLE DISTILLATION
1) place mixture in conical flask, with bung in top with thermometer
2) connect conical flask to condenser (tube with cold water flowing around it) and a beaker at the other end
3) heat conical flask
4) vapour will rise into condenser, condense and collect in beaker

Question 4

Describe a practical to separate a mixture of liquids with different boiling points.

Answer 4

a mixture of liquids:
FRACTIONAL DISTILLATION
1) mixture in conical flask, connected to fractional column (tube with glass balls) with thermometer at top, connected to condenser and beaker
2) gently heat mixture
3) both liquids evaporate, but when hit fractional column, they condense
4) the one with the lowest point goes through fastest as it is the easiest to evaporate
5) when thermometer reads above lowest boiling point, swap beaker
6) repeat for next liquids

Question 5

Describe a practical to separate substances based on their solubilities.

Answer 5

substances (solubilities):
CHROMATOGRAPHY
1) draw pencil line near bottom of chromatography paper (insoluble)
2) draw dots of colour on line
3) place paper in solvent up to line (liquid that will dissolve the substances)
4) the solvent will move up the paper, carrying the ink with it at different speeds due to solubility and attraction to paper
5) end result is a chromatogram

• paper is stationary phase (doesn’t move)
• solvent is mobile phase (moves)
• if forms single spot, a pure substance
• if forms separate spots, mixture

Question 6

Describe a practical to make a soluble solid with a dilute acid and metal oxide or carbonate.

Answer 6

making soluble salts:

1) start with fixed volume of dilute acid
2) gently heat until almost boiling
3) use spatula to add metal oxide or carbonate and stir with glass rod
4) stop when no more base dissolves as neutralisation is complete
5) filter
6) place in evaporating basin whilst gently heating over boiling water
7) heat until half solution remains
8) leave for 24 hours in a cool place
9) scrape crystals onto paper towel and gently pat
- forms dry salt crystals

Question 7

Describe a practical to find the exact volume of acid needed to neutralise a fixed volume of alkali. What are the different indicators and what colour do they turn in alkalis and acids?

Answer 7

titrations:

1) use pipette to transfer 25 cm cubed of alkali to conical flask
2) add indicator
3) place on white tile to see colour change more clearly
4) fill burette with acid (variable volume)
5) add acid to alkali until neutral (colour change), swirl
6) read volume of acid on burette

• phenophthalein - colourless in acid, pink in alkali
• litmus - red in acid, blue in alkali
• methyl orange - red in acid, yellow in alkali

Question 8

Describe a practical to investigate electrolysis and the products from it.

Answer 8

electrolysis:

1) pour 50 cm cubed of ionic compound into beaker
2) place plastic petri dish over beaker with two holes for the electrodes
3) place electrodes into each hole
4) attach crocodile clips to rods and connect to low voltage power supply
5) select 4V and switch on

• chlorine will bleach damp litmus paper
• hydrogen will pop lit splint
• oxygen will relight glowing splint

Question 9

Describe a practical to investigate variables that affect temperature changes in chemical reactions.

Answer 9

investigating temperature changes:

1) measure 30 cm cubed of acid
2) transfer to polystyrene cup (insulator) and put cup into beaker
3) use thermometer to measure initial temperature
4) measure 5 cm cubed of reactant
5) transfer to polystyrene cup and place lid on with hole for thermometer
6) gently stir
7) record highest temperature reached
8) repeat with more reactant
9) plot graph