Core practicals

Question 1

What happens during paper chromatography? (method)

Answer 1

1) ink spots are drawn on a pencil line at the bottom of a piece of paper
2) The piece of paper is dangles in the solvent, ensuring that the solvent is below the pencil line
3) Leave the solvent to travel up the paper and then remove before the solvent reaches the top of the paper.
4) mark the point at which the solvent reaches of the paper.
5) calculate the Rf value (distance travelled by spot/distance travelled by solvent)

Question 2

What is the stationary phase and mobile phase in chromatography?

Answer 2

Stationary phase: It is the substance which does not move e.g. the paper
Mobile phase: the substance that moves through the stationary phase e.g. the solvent

Question 3

Why do some substances travel further up the paper than other substances in chromatography?

Answer 3

Because some substance form stronger bonds with the stationary phase (solvent) whereas others from stronger bonds with the mobile phase (solvent).

Question 4

What is the salts from insoluble bases practical?

Answer 4

1) Add a base in excess to an acid
2) Filter out the unreacted base ( copper oxide)
3) slowly evaporate the water to be left with salt crystals

Question 5

What is a titre?

Answer 5

The exact amount of acid added to exactly neutralise an alkali

Question 6

How do you perform a titration?

Answer 6

1) put an acid in a burette
2) use a pipette to put a known volume of alkali into a conical flask
3) put a few drops of suitable indicator solution such as phenolphthalein into the alkali
4) record the burette level and start reading
5) add acid to the alkali and swirl the flask until the colour changes and record the burette end reading
6) use the start and end point to calculate the exact volume of acid used

Question 7

Why must a titration be used to produce a salt from a soluble base?

Answer 7

Titration lets you find the correct proportions of acid and alkali to mix together to produce a solution that contains only a salt and water as otherwise there will be excess alkali.

Question 8

How can you make your titre more accurate?

Answer 8

• swirl the flask contain the alkali continuously
• near the end point, add the acid drop by drop
• clamp the burette vertically at eye level and take the meniscus into consideration