Topic 8- Chemical analysis

Question 1

What is a pure substance?

Answer 1

A pure substance is a single element or compound, not mixed with any other substance.

Question 2

What is a formulation and how is it made?

Answer 2

• A formulation is a mixture of compounds in measured quantities that has been designed as a useful product.
• Examples: paints, medicines, alloys, fertilisers.

Question 3

Describe paper chromatography

Answer 3

1) A line is drawn at the bottom of the paper with spots of ink on the line.
2) A beaker is filled with a small amount of solvent (it cannot touch the line)
3) Paper is hung on a rod and placed in a beaker.
4) Solvent travels up the paper, thus separating the components.
5) Before solvent reaches the end, the paper is taken out and the finish line is marked, paper is dried.
6) paper stationary phase, solvent mobile phase.

Question 4

How is Rf calculated?

Answer 4

distance moved by the spot ÷ distance moved by solvent

Question 4

Describe the test for:

1) Chlorine
2) Oxygen
3) Carbon dioxide
4) Hydrogen

Answer 4

1) litmus paper, turns white
2) glowing splint, relights
3) shakes with lime water, cloudy
4) lit splint, end of tube, pop sound

Question 4

Describe the flame test result:

Answer 4

Lithium compounds- crimson red flame
sodium compounds- yellow flame
potassium compounds- lilac flame
calcium compounds- orange red flame
copper compounds- green flame

Answer 5

Instrumental methods of analysis are faster, and more accurate and sensitive than simple chemical tests.

Question 6

Describe the test for carbonate ions:

Answer 6

Add dilute acids e.g Hcl

fizzing is observed, as co2 is released

Question 7

Describe the test for sulphate ions:

Answer 7

Add a solution containing ba2+ cations, e.g. a solution of BaCl2
White precipitate of BaSo4 forms
e.g. K2So4 + Bacl2 = 2kcl +Baso4