Chemical analysis

Question 1

Formula for rf values

Answer 1

distance travelled by component divided by distance travelled by solvent

Question 2

Paper chromatography (rp)

Answer 2

Separates mixtures in a solution.

1. Using a ruler draw a pencil line 2cm from the short edge of the chromatography paper.

Mark 5 pencil spots at equal intervals across the line, keeping at least 1cm away from each end.

2. Use a glass capillary tube to put a small spot of each known colouring and the unknown one onto the 5 pencil spots.

Try to make sure each spot is no more than 5mm in diameter. Label each spot in pencil.

3. Pour water into the beaker to a depth of no more than 1cm
4. Attach the edge of the paper furthest from the spots to a glass rod so when the rod is rested o the top edge of the beaker, the bottom edge of the paper dips into the water. Ensure that the pencil line is above the water surface, and that the sides of the paper do not touch the beaker wall.
5. Without disturbing the beaker, wait for the water solvent to travel at least three quarters of the way up the paper. Carefully remove it and draw another pencil line on the dry part of the paper as close to the wet edge as possible.
6. Hang the paper up to dry thoroughly
7. Measure the distance in m between the two pencil lines. This is the distance travelled by the water solvent. Write the same distances for each colouring in a table.
8. For each of the four known colours, measure the distance in from the bottom line to the centre of each spot. Write each measurement i. the table.
9. use the rf equation (insert) to calculate the Rf value for each of the known colours. Write these in the table.
10. match the spots in the unknown sample U with those from A - D using the colour and distance travelled. look for those which match and those which do not.

Question 3

Paper chromatography outlined

Answer 3

Use rectangular chromatography paper suspended in large beaker to separate mixed dyes alongside the pure components of the mixtures, using water, ethanol and/or water-ethanol mixtures as solvent. Dry, take measurements and compare the effect of different solvents on Rf values.

Question 4

In chromatography, what phase is the paper?

Answer 4

the stationary phase

Question 5

In chromatography, what phase is the solvent?

Answer 5

the mobile phase