3 - Separation and purification Flashcards
Define what is a mixture
Mixture is made up of 2< substances that are NOT chemically combined
Possible states that can be separated from one another in a mixture
- Solid from liquid
- Solids
- Liquid from solution
- Liquids
Describe how filtration is carried out
separating solid from liquid
- Pour mixture into a filter funnel lines with filter paper
- Collect filtrate (the liquid) in a beaker
- Collect residue and dry it on a piece of filter paper
What is TYPICALLY the main aim of filtration?
To get the residue
What is the purpose of ‘evaporate to dryness’ ?
Obtain SOLUBLE SOLID from a solution until all the water is boiled off
(Not always pure as soluble impurities would be left with the solid)
Define the purpose/ aim of crystallisation
Obtain pure (soluble) solid from solution
Describe the procedure of crystallisation (5 steps)
- Dissolve the solid in water
- Filter to remove the excess insoluble substance
- Heat the solution till its saturated (that’s when crystals start forming)
- When solution is saturated, leave it to cool and crystallise
- Filter to collect the crystals, wash it with a little cold distilled water to remove impurities, dry crystals with filter paper
What is a solvent/ solute?
Solute - the solid
Solvent - The liquid that DISSOLVES the solute
What are the common solvents?
Water and ethanol
Purpose of sumbilation
To separate a solid that sublimes from one that does not
Magnet (separation technique, purpose)
A magnet can be used to separate a magnetic substance from a non-magnetic substance
Purpose of simple distillation
Separate a pure solvent (liquid) from a solution
Describe the process of simple distillation
- Solution boils in distillation flask
- Boiling chips added to ensure smooth boiling
- Water vaporise, rises and enters the condenser
- In condenser, water vapour is cooled
- Vapour condenses and changes back into pure water
- Distillate is collected in the receiver (beaker/ flask)
- Solid residue would be left in the flask
Where the thermometer is put in simple distillation, and why it is put there
Procedure: Placed beside the side arm of the distillation flask
Reason: Ensures the thermometer measures the boiling point of the substance that is being distilled, and not the flame
How should a condenser be placed in simple distillation set up
Procedure:
- Condenser should slop downwards
- Cold running water is allowed to enter from the bottom while the water exits from the top
Why does water enter from the bottom of the condenser and exit from the top
To ensure a permanent cool surface to condense the vapour effectively before it leaves the condenser
Procedure and reason for a receiver (thing to collect distillate) in simple distillation
Procedure: If the distillate is volatile (easily evaporated), the receiver can be put in a tub of ice
Reason: Helps to keep the temperature of the distillate low so that it remains in the liquid state
Purpose of a separating funnel
To separate 2 immiscible liquids (e.g water and oil)
Describe the process of using a separating funnel
- Pour the mixture of oil and water into the separating funnel
- Support the separating funnel using a report stand, then put clean beaker below
- Allow liquids to separate completely
- Open tap of the funnel to allow the bottom liquid to drain into the beaker. Close the tap before the top layer runs out.
- Place another clean beaker below and drain the rest of the top layer.
Purpose of fractional distillation
Separate a mixture of miscible liquids with diff BOILING points.
Purpose of tall fractionating column in fractional distillation
It increases TSA for condensation so liquids can be separated effectively (this is cus evaporation exists ._.)
Describe the process of fractional distillation
e.g water and ethanol
- Ethanol vapour and water vapour rise up the column as the solution is heated
- The water vapour condenses in the fractionating column as the solution is heated
- Ethanol, which has a lower boiling point than water, reaches the upper part of the column and is distilled over
- The thermometer shows a constant temp. of [insert temp.] which is the boiling point of ethanol
- In the condenser:
- Hot ethanol vapour condenses as running water cools it;
- Liquid ethanol glows down the inner tube of the condenser and into the receiver - Ethanol is collected as the distillate in the receiver
Purpose of paper chromatography
Method to separate 2< components that dissolve in the same solvent (It’s a mixture i think)
Describer the procedure of paper chromatography
- Draw a line 1cm from the bottom of a strip of filter paper or chromatography
- Put the [dye or smth] on the pencil line and allow the drops to dry
- Dip paper into a glass tank containing the solvent. The solvent would then be soaked up by the paper to dissolve the [dye, or ink or smth]
- Leave the apparatus to stand for a while. The solvent would travel up the paper, carrying the [dye/ ink] along. Which every is more soluble would travel up higher.
Types of solvent for paper chromatopography
- water (universal solvent)
- Ethanol (organic solvent)
How to calculate the Rf value?
AND
What is an Rf value?
Distance travelled by the substance/ distance travelled by the solvent
(Note: 3sf, value is equal to or less than 1)
It is the retention factor of the substance (because the distance the substance travelled is dependent on the duration of experiment)
Why must the level of the solvent be lower than the starting line?
So the sample does not dissolve in the solvent before the separation
Uses of paper chromatography
- Separate the components in a sample
- Identify components present in a sample
- Identify substances
- Determine whether a sample is pure
How to determine the purity of a substance?
Melting point (solid) / boiling point (liquid)
How would impurities affect m.p/ b.p
Lower melting point (solid) Increase boiling point (liquid)
[Note: this applies MOST of the time]
