Purity, Formulations and Chromatography

Question 1

describe what a pure substance is

Answer 1

a single element or compound not mixed with any other substance

pure elements and compounds melt and boil at specific temperatures - this can be used to distinguish pure substances from mixtures

Question 2

describe what a formulation is and give examples

Answer 2

a mixture that has been designed as a useful product

eg: fuels, cleaning agents, paints, medicines

Question 3

describe how paper chromatography can separate mixtures

Answer 3

• draw a pencil line across the chromatography paper
• use a pipette to add small spots of each ink to the line on the paper as well as unknown ink
• place the paper into a container with a suitable solvent in the bottom - making sure that the pencil line is above the water line
• allow the solvent to move through the paper, but remove before it reaches the top
• allow to dry and then measure the distance travelled by each spot and the solvent

Question 4

suggest how chromatographic methods can be used for distinguishing pure substances from impure substances

Answer 4

• a pure substance produces one spot on the chromatogram

- an impure substance produces two or more spots