8.1 Purity, formulations, and chromatography

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.

Question 3

Give examples of formulations.

Answer 3

● Fuels
● Cleaning agents
● Paints
● Medicines
● Alloys
● Fertilisers
● Foods

Question 4

Describe paper
chromatography

Answer 4

1. A start line is drawn near the bottom of the paper. The mixture is spotted on the line.
2. A beaker is filled with a small amount of solvent (it cannot touch or go above the start line when paper is placed in a beaker)
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 level reaches the end, the paper is taken out and the finish line is
   marked. The paper is dried.
6. The procedure works when different compounds have different affinities for the solvent/paper. Stronger attraction for the paper - travels slowly with the solvent etc.
7. Paper is called the stationary phase - it doesn’t move. Solvent is the mobile phase.

Question 5

How is Rf
calculated?

Answer 5

Distance moved by the spot / distance moved by solvent

Question 6

In a paper chromatography experiment,
a compound A was found to have an Rf value of 0.85 - what does it tell you about
the compound?

Answer 6

It has a higher affinity for the solvent than for the paper.