Separating Substances 🔥 Flashcards
What is a pure substance?
A substance which consists of a single element or compound which contains no other substances.
What is a mixture?
Two or more elements or compounds that are physically mixed together, they are not chemically bonded.
What is air an example of?
A mixture
What is a characteristic of pure substances?
Melt and boil at specific and sharp temperatures e.g pure water has a boiling point of 100°C and a melting point of 0°C.
What would a pure substance look like on a heating/cooling curve?
The horizontal part of the graph would show a sharp melting point.
E.g https://cdn.savemyexams.co.uk/cdn-cgi/image/w=1280,f=auto/uploads/2020/02/Purity-Pure-Substance-Cooling-Curve.png
What would an impure sample look like on a heating/cooling curve?
Produce a gradual decrease/increase in temperature.
E.g https://cdn.savemyexams.co.uk/cdn-cgi/image/w=1280,f=auto/uploads/2020/02/Purity-ImPure-Substance-Cooling-Curve.png
What is a compound?
Contains two or more types of atom bonded/joined together.
What is simple distillation used to separate?
A liquid and a soluble solid from a solution
OR
A pure liquid from a mixture of liquids
Give a brief outline of simple distillation.
- solution is heated and pure water evaporates producing a vapour which rises.
- the vapour passes through the condenser, where it cools and condenses, turning into the pure liquid that is collected.
- only the solid solute will be left behind.
What is fractional distillation used to separate?
Different liquids from a mixture of liquids.
Give a brief outline of fractional distillation.
- the solution is heated to the temp of the substance with the lowest boiling point.
- this substance will rise and evaporate first, and vapours will pass through a condenser and will be collected.
- this leaves behind the other component(s) of the mixture.
What is filtration used to separate?
An insoluble solid from a liquid.
Give a brief outline of filtration.
- A piece of filter paper is placed in a filter funnel above a beaker.
- The mixture is poured into the filter funnel.
- The filter paper will only allow small liquid particles to pass through a filtrate.
- solid particles are too large so will stay behind as a residue.
What is crystallisation used to separate?
A dissolved solid from a solution
Give a brief outline of crystallisation.
- A solution is placed in an evaporating basin and heated.
- Some water evaporates and solid particles begin to form.
- All the water evaporates which labels solid crystals.
What is paper chromatography used to separate?
Mixtures of soluble substances. (E.g inks)
Why is pencil used in paper chromatography to draw a start line?
Ink would run into the chromatogram along with the samples.
Should the pencil line sit above or below the level of solvent?
Above so the samples don’t wash into the solvent container.
Will substances with higher solubility travel further?
Yes
How many spots will an impure substance show up with?
More than one
What is the stationary phase in paper chromatography?
The paper
What is the mobile phase in paper chromatography?
The solvent
Give a brief outline of paper chromatography.
- pencil line is drawn and spots of ink are placed on it.
- the paper is lowered into the solvent container.
- the solvent travels up the paper taking some coloured substances with it.
- substances will spread apart, showing different components of the ink / dye .
How many spots does a pure substance produce on a chromatogram?
One spot
