What is the composition of a pure substance?
- Cannot be changed
- Is the same in all parts of a piece of the substance
What is a substance’s melting point an example of?
A physical property.
What is crystallisation?
The process of evaporating a solvent to leave solutes behind.
What is a saturated solution?
A solution that contains the maximum amount of solute that can dissolve in that amount of solvent at that temperature.
What is the apparatus required for filtration?
- Filter paper
- Suspension
- Solid residue
- Filter funnel
- Filtrate
What is the process of filtration?
- Filter funnel is lined with filter paper
- Solvent and solute pass through the fine holes of the filter paper to form the filtrate
- Bits of insoluble substances cannot fit through the holes and so leave a residue in the filter paper
- A Bunsen burner is used to evaporate the filtrate carefully
- This must be done with care as to not overheat the solution once it is saturated because hot crystals may spit out. Further heating may also cause crystals to change chemically
What is the apparatus required in crystallisation?
- Filtrate
- Evaporating basin
- Boiling water
- Gauze
How can we reduce the risk of a hazard during crystallisation?
- Wear eye protection to reduce risks from spitting
- Remove Bunsen burner before solution is completely dry and/or use steam to heat the evaporation basin gently
What can we use paper chromatography for?
- Distinguishing between pure and impure substances
- Identifying substances by comparing the pattern on the chromatogram with the patterns formed by known substances
- Identifying substances by calculating their Rf values
How do we calculate the Rf value in chromatography?
distance moved by the spot
Rf = _________________________________
distance moved by the solvent
What is the apparatus required for the ‘investigating inks’ chromatography experiment?
- Conical flask
- Collecting tube
- Boiling tube
- Thermometer
- Tripod
- Gauze
- Bunsen burner
- Large beaker of ice
- Anti-bumping granules
- Ink solution
- Chromatography paper attached to pencil or glass rod
- Beaker
- Water soluble pens
- Pencil and ruler
What is the method used to perform simple distillation on the ink solution?
- Add anti-bumping granules to a conical flask
- Add ink solution and place the flask on a tripod and gauze
- Attach collecting tube which leads into a boiling tube in an ice bath
- Heat so that the temperature remains at about 100°C and until a colourless liquid appears in the boiling tube
- You should have collected a sample of distilled water with no colour from the ink within the sample
What is the method used to perform chromatography?
- Take chromatography paper and draw a pencil line 2cm from the bottom of the page
- Put one or two small ink marks on the line
- Attach the other end to a pencil or rod that is long enough to go over the edges of a beaker
- Fill the beaker up to 1cm and place in the chromatography paper so that the water level is below that of the pencil line
- Wait until the water solvent has run up the paper and dry before the ink reaches the top of the paper
- Calculate the Rf value by dividing distance of solute from the pencil line over distance of solvent (should be less than 1 and different for different colours in ink)
What are possible issues and improvements to the method?
- Ensure about 3/4 of the boiling tube is submerged in the ice water
- Control temperature of the ink solution using thermometer and closing the gas tap when required
- Use small ink spots which are well spread out on pencil line to ensure colours don’t run into each other
- Measure distance of solute from the centre of the ink spot
What are the control variables of the simple distillation in the chromatography experiment?
Temperature should remain at 100°C.
What are safety precautions for the chromatography experiment?
- Wear eye protection to protect against splashes from boiling water
- Use anti-bumping granules to prevent solution boiling over
What is the apparatus required for a distillation experiment?
- Distillation flask
- Condenser
- Distillate
- Thermometer
- Anti-bumping granules
What do anti-bumping granules do?
They make the liquid boil more smoothly - small bubbles of vapour form on the corners of the granules and reduce the risk of the liquid boiling over.
Where can fractional distillation be used?
- To separate the different products in crude oil
- To make alcoholic drinks such as whisky and vodka
- To separate out the gases in the air, after the air has been cooled and turned into a liquid at -200°C
What is the apparatus required in fractional distillation?
- Round bottom flask
- Fractionating column
- Condenser
- Distillate
- Thermometer
What is desalination?
Producing pure water from sea water using simple distillation.
Why is desalination not usually suitable for producing large volumes of drinking water?
Lots of energy must be transferred to sea water during simple distillation. It is mainly carried out on a large scale where energy resources are cheap or plentiful and where there is an abundant supply of sea water.
What does fresh water stored in reservoirs contain?
- Objects (such as leaves and twigs)
- Small insoluble particles (such as grit and silt)
- Soluble substances (such as salts, pesticides and fertilisers)
- Bacteria and other microorganisms that may be harmful to health
What processes are used to remove things in fresh water?
- Screening using a sieve
- Sedimentation
- Filtration
- Chlorination
