Separating and purifying substances

Question 1

What is pure mean

Answer 1

If a substance is completely made up of a single element or compound

Question 2

What is a mixture

Answer 2

He substance that is made up of more than one element or compound

Question 3

What is a pure substance’s melting point like

Answer 3

It has a specific, sharp melting and boiling point

Question 4

How can you use melting and boiling points to test the purity of a substance

Answer 4

By comparing the actual melting point of the sample to the expected value

Question 5

What is a mixture’s melting and boiling point like

Answer 5

It will melt gradually over a range of temperatures rather than having a sharp melting point

Question 6

What mixtures can be separated using simple distillation

Answer 6

It is used to separate out a liquid from solution

Question 7

What mixtures can be separated using fractional distillation

Answer 7

If you have a mixture of many different liquids

Question 8

What mixtures can be separated using filtration

Answer 8

An insoluble solid from a liquid

Question 9

What mixtures can be separated using crystallisation

Answer 9

A soluble solid from a solution

Question 10

What substances can be separated using paper chromatography

Answer 10

A mixture of soluble substances (like ink)

Question 11

What is paper chromatography

Answer 11

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

Question 12

What is the mobile phase in paper chromatography

Answer 12

Where the molecules can move up the paper and separate (due to the solvent)

Question 13

What is the stationary phase in paper chromatography

Answer 13

When the Molecules can no longer move up the paper (solvent has been used up.) You are left with a thick liquid or solid

Question 14

What does a pure substance look like on a chromatogram

Answer 14

It will be a single spot (colour) of ink and nothing else

Question 15

What will an impure substance look like on a chromatogram

Answer 15

It will be many different spots (colours)

showing the different molecules in the solution

Question 16

what is Rf value

Answer 16

The ratio between the distance travelled by the dissolved substance and the distance travelled by the solvent.

Question 17

What equation do you use to calculate the Rf value

Answer 17

Rf =

distance travelled by solute/distance travelled by solvent

Question 18

How do you measure the distance travelled by the solute

Answer 18

Measure from the baseline to the centre of the spot

Question 19

How do you measure the distance travelled by solvent

Answer 19

Measure from the baseline to the solvent line

Question 20

What can Rf values tell you

Answer 20

🏮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