Separating and purifying substances Flashcards
What is pure mean
If a substance is completely made up of a single element or compound
What is a mixture
He substance that is made up of more than one element or compound
What is a pure substance’s melting point like
It has a specific, sharp melting and boiling point
How can you use melting and boiling points to test the purity of a substance
By comparing the actual melting point of the sample to the expected value
What is a mixture’s melting and boiling point like
It will melt gradually over a range of temperatures rather than having a sharp melting point
What mixtures can be separated using simple distillation
It is used to separate out a liquid from solution
What mixtures can be separated using fractional distillation
If you have a mixture of many different liquids
What mixtures can be separated using filtration
An insoluble solid from a liquid
What mixtures can be separated using crystallisation
A soluble solid from a solution
What substances can be separated using paper chromatography
A mixture of soluble substances (like ink)
What is paper chromatography
The separation of mixtures of soluble substances by running a solvent through the mixture of the paper which causes the substance to move at different rates over the paper
What is the mobile phase in paper chromatography
Where the molecules can move up the paper and separate (due to the solvent)
What is the stationary phase in paper chromatography
When the Molecules can no longer move up the paper (solvent has been used up.) You are left with a thick liquid or solid
What does a pure substance look like on a chromatogram
It will be a single spot (colour) of ink and nothing else
What will an impure substance look like on a chromatogram
It will be many different spots (colours)
showing the different molecules in the solution
what is Rf value
The ratio between the distance travelled by the dissolved substance and the distance travelled by the solvent.
What equation do you use to calculate the Rf value
Rf =
distance travelled by solute/distance travelled by solvent
How do you measure the distance travelled by the solute
Measure from the baseline to the centre of the spot
How do you measure the distance travelled by solvent
Measure from the baseline to the solvent line
What can Rf values tell you
🏮If you need to see if a certain substance present in the mixture you can run a pure sample of the substance alongside the sample of the mixture.
🏮If the sample has the same Rf values as one of the spots they are likely to be the same
