purity, formulations and chromotography (topic 8)

Question 1

describe how the student can use the apparatus to find out which colour dyes are in the ink sample: chromatography paper, pencil, ruler, container of water, ink sample (4)

Answer 1

• draw a pencil line 1-2 cm from the bottom of the chromatography paper
• put a drop of the ink sample on the pencil line
• suspend the chromatography paper so that the bottom of the paper is dipped in a container of water
• leave until water front has reached the top of the paper
• observe separated ink sample and compare to known inks

Question 2

why sample made of brand b ink (2)

Answer 2

• brand B has spots of dye at the same height
• brand A and C do not have an identical pattern of spots

Question 3

state two measurements the student should take to calculate the Rf value of the 3rd spot in the sample (2)

Answer 3

• the distance moved by the dye
• the distance moved by the water

Question 4

Answer 4

Question 5

plan an investigation to determine the Rf value for the dye in a food colouring sample (6)

Answer 5

• draw pencil start line on chromatography paper 1-2 cm from bottom of paper
• place spot of food colouring on start line
• use of a suitable solvent
• place solvent in beaker/container
• suspend chromatography paper so that the bottom of the paper is in the solvent
• wait for the solvent to travel up the chromatography paper (until near the top)
• mark solvent front
• dry the chromatography paper
• measure distance between start line and centre of spot
• measure distance between start line and solvent front
• then Rf value calc

Question 6

explain why the start line is pencil and not ink (2)

Answer 6

• ink dissolves in solvent
• and travels up the chromatography paper
• the pencil line will not be affected by the solvent travelling up the paper

Question 7

the student measures the solvent front and distance to the colouring to be 3.2 and 4.9 cm respectively, calculate the Rf value for the food colouring

Answer 7

Question 8

Answer 8

Question 9

Answer 9

Question 10

and stationary phase

Answer 10

• mobile, water
• stationary, chromatography paper

Question 11

(2)

Answer 11

• ink A and ink C are in the sample
• they have spots of dye at the same distance as those in the sample
• it cant be ink B because the distances don’t completely match

Question 12

the student mixes ink A and ink B together, describe how the overall Rf value of the new sample compares to that in part c (3)

Answer 12

• new Rf value is lower
• as ink B contains a dye with a low Rf value
• as shown by a spot of dye low on the chromatography paper

Question 13

explain what is meant by the term formulation (3)

Answer 13

• mixture designed as a useful products
• made by mixing the components in carefully measured quantities
• each component has a particular purpose
• and the overall mixture has the desired properties

Question 14

give one example of a formulation

Answer 14

• paint
• medicines
• fuels

Question 15

describe the role of the pigment in paint

Answer 15

provides colour

Question 16

describe the role of the solvent in paint (2)

Answer 16

• helps the pigment and binder spread well during painting
• by thinning them out

Question 17

sample A is a sample of water which also contains salt impurities, describe how to obtain pure water from sample A (4)

Answer 17

• distillation
• heat the sample using a bunsen burner
• vapour/steam enters the condenser and steam condenses into water
• collect the condensation in a container
• the liquid collected will be pure water

Question 18

rf value equation

Answer 18

dye/water