Chemistry - 12 Chemical Analysis - 12.1 Pure Substances and Mixture & 12.2 Analysing Chromatograms

Pure substance

sample of matter made up of just one element or compound

Fixed point

melting and boiling point of a substance

How can you test that a sample is pure?

sample changes state all at once, rather than over a range of temperatures

A pure substance changes state...

at a fixed temperature

A mixture changes state...

over a range of temperatures

Impurities tend to ... the melting point and ... the boiling point

lower, raise

Formulation

mixture that has been designed as a useful product

Common formulations [5]

- medicine

- paint

- cleaning agents

- fuels

- food products

Non-active ingredients in medicine [7]

- colorants

- sweeteners

- coatings

- fillers

- binding agents

- ingredients to aid dissolving in effective part of GI tract

- ingredients to prevent upset stomach

Ingredients in paint [3]

- pigment

- binder

- solvent

Function of binder in paint

causes paint to adhere to surfaces and form a protective film

Function of solvent in paint

causes pigment and binder to spread well by thinning

Ingredients in cleaning agents [4]

- surfactant

- water

- colouring and fragrance additives

- rinse agent

Function of surfactant in cleaning agents

detergent which removes grease

Function of rinse agent in cleaning agents

allows water to drain off crockery

Chromatography

laboratory technique used to separate mixtures of molecules based on solubility

Paper chromatography

technique used to separate and observe the different pigments in a material by their solubility in a solvent on paper

Phases of chromatography [2]

- mobile phase

- stationary phase

Mobile phase

phase that moves in chromatography

Stationary phase

phase that does not move in chromatography

The substance which travels the most has the strongest attraction to the (solvent/paper)

solvent

The substance which travels the least has the strongest attraction to the (solvent/paper)

paper

Adsorb

to attract and stick to a surface

How can unknown substances be identified using chromatography?

separated substances on a chromatogram can be compared with a database of other substances

Retention factor

ratio that represents how far a compound travels in a particular solvent

Retention factor (Rբ) =

(distance moved by substance) ÷ (distance moved by solvent)

Why is chromatography data stored as retention factors?

it eliminates the effects of other factors, so variables do not need to be closely controlled each time a chromatogram is created