Combined Chemistry - C8 Chemical Analysis

Question 1

What is the chemical meaning of a ‘pure’ substance?

What is the every day meaning of a ‘pure’ substance?

Answer 1

In Chemistry: A single element or compound that is not mixed with any other substance.

In everyday language: A substance that hasn’t had anything added to it, e.g. pure milk.

Question 2

What data can be used to prove a substance is ‘pure’ and not a mixture?

Answer 2

Melting and Boiling points (because pure substance melt and boil at specific temperatures)

Question 3

What is a formulation?

Answer 3

A mixture that has been designed as a useful product.

Question 4

Give three examples of formulations

Answer 4

Any three from:

Fuels, cleaning agents, paints, medicines, alloys, fertilisers and foods.

Question 5

Name the two phases in chromatography.

Answer 5

• Stationary Phase
• Mobile Phase

Question 6

In Chromatography, how do you calculate the R_f value for a substance?

Answer 6

R_f = distance moved by substance / distance moved by solvent

Question 7

What will the chromatogram of a pure substance look like?

Answer 7

A pure substance will only show a single spot on the chromatogram.

Question 8

Explain how paper chromatography can be used to separate a mixture.

Answer 8

• A substance is added to the chromatography paper (stationary phase).
• Molecules within a substance dissolve in the solvent and move up the paper (mobile phase).
• The molecules within the substance separate because different chemicals spend different amounts of time in the mobile and stationary phases and therefore move different distances up the paper.

Question 9

Describe how you would test for Hydrogen.

Answer 9

• Collect gas in a test tube
• Hold a burning splint at the open end of a test tube.
• You will hear a ‘pop’ sound if Hydrogen is present

Question 10

Describe how you would test for Oxygen.

Answer 10

• Collect gas in a test tube
• Insert a glowing splint into the test tube
• The splint will relight if oxygen is present

Question 11

Describe the test for Carbon dioxide.

Answer 11

• Bubble the gas through limewater (calcium hydroxide solution)
• If the limewater turns milky (cloudy) then carbon dioxide is present

Question 12

Describe the test for Chlorine.

Answer 12

• Collect gas in a test tube
• Place damp litmus paper in the test tube
• If chlorine is present, the litmus paper is bleached and turns white