chemical analysis (p2)

Question 1

What is a pure substance?

Answer 1

A single element or compound that is not mixed with any other substance

Question 2

What type of substances melt and boil at specific temperatures?

Answer 2

Pure substances

Question 3

If a substance boils between 55 and 58 ᵒC, will it be pure or impure?

Answer 3

impure

Question 3

What type of substances melt and boil over a range of temperatures?

Answer 3

Impure substances

Question 4

Is carbon dioxide pure or impure?

Answer 4

pure

Question 5

Is oxygen pure or impure?

Answer 5

pure

Question 6

What is a formulation?

Answer 6

A mixture that has been designed as a useful product

Question 6

Is water from a tap pure or impure?

Answer 6

Impure as contains dissolved salts

Question 7

Are formulations pure or impure?

Answer 7

Impure

Question 8

What is chromatography used to separate?

Answer 8

Mixtures of soluble susbtances

Question 9

Name the two phases in chromatography

Answer 9

Stationary phase - where molecules can’t move
Mobile phase - where molecules can move

Question 10

What phase is the paper in chromatography?

Answer 10

Stationary phase

Question 11

What phase is the water in chromatography?

Answer 11

Mobile phase

Question 12

Why do substances separate in paper chromatography?

Answer 12

Substances move up the paper when they are dissolved in the solvent
The different substances have different solubilities in the solvent
Therefore they travel different distances up the paper

Question 13

How could you tell if a substance was impure by looking at a chromatogram?

Answer 13

There would be more than one spot in a vertical column above the original spot

Question 14

How could you tell if a substance was pure by looking at a chromatogram?

Answer 14

There would be only one spot in a vertical column above the original spot

Question 15

Why should the baseline be drawn in pencil?

Answer 15

Pencil is insoluble
If it was drawn in pen the ink would dissolve and so the line would run

Question 16

Why should the level of water be below the baseline?

Answer 16

If it was above the baseline the spots would wash off the paper

Question 17

What is the solvent front?

Answer 17

The distance travelled by the solvent

Question 18

When should you remove the chromatography paper?

Answer 18

When the solvent has nearly reached the top

Question 19

Why is the chromatography paper often attached to a glass rod when carrying out chromatography?

Answer 19

So that it stands up in the water

Question 20

Why should a lid be placed on the beaker during chromatography?

Answer 20

To saturated the atmosphere in the beaker with solvent vapour

prevent evaporation

Question 21

The higher the Rf value the ………. the distance travelled by the substance

Answer 21

Greater

Question 22

What equation is used to calculate Rf values?

Answer 22

Rf value = distance travelled by spot ÷ distance travelled by solvent

Question 23

How many spots will a pure susbtances produce on a chromatogram?

Answer 23

one

Question 24

Describe how you would set up a chromatogram

Answer 24

- Draw a baseline in pencil near the bottom of a piece of filter paper - Add a spot of ink to this line and allow it to dry - Place the paper in a beaker of solvent (usually water), make sure the level of solvent is below the baseline - Add a lid to the beaker to stop the solvent evaporating - Allow the solvent to run up the paper - Remove the paper from the beaker just before the solvent reaches the top of the paper

Question 24

What is the test for oxygen?

Answer 24

- Use a glowing splint - If oxygen gas is present the glowing splint will relight

Question 25

What is the test for hydrogen?

Answer 25

- Use a burning splint - If hydrogen is present it will burn with a squeaky pop

Question 26

What is the test for carbon dioxide?

Answer 26

- Bubble gas through limewater (calcium hydroxide solution) - If the gas is carbon dioxide the limewater will turn from colourless to milky

Question 27

What is the test for chlorine?

Answer 27

- Add damp litmus paper - If chlorine gas is present the litmus paper is bleached and turns white