Chemical Analysis

define pure substance

An element or compound that is not mixed with any substances

Give three example of a pure substance

1. gold

2. water

3. oxygen gas

A pure substance melts at

Specific fix temperature

What is a formulation and how is it made? Give examples

- A formulation is a mixture of compounds in measured quantities that has been

designed as a useful product.

- Formulations include fuels, cleaning agents, paints, medicines, alloys,

fertilisers and foods.

- E.g. alloys are mixtures of metals; they are harder than pure metals, so have

a particular purpose.

Describe paper chromatography.

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 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.

How is Rf calculated?

Distance moved by the spot divided by distance moved by solvent

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

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

Describe the test for hydrogen

The test for hydrogen uses a burning splint held at the open end of a test tube of the gas. Hydrogen burns rapidly with a pop sound.

Describe the test for oxygen

The test for oxygen uses a glowing splint inserted into a test tube of the gas. The splint relights in oxygen.

Describe the test for carbon dioxide

The test for carbon dioxide uses an aqueous solution of calcium hydroxide (lime water). When carbon dioxide is shaken with or bubbled through limewater the limewater turns milky (cloudy).

Describe the test for chlorine 

The test for chlorine uses litmus paper. When damp litmus paper is put into chlorine gas the litmus paper is bleached and turns white.