5.8.1 Purity, formulations and chromatography

what is an Rf value in a chromatogram?

the ratio between the distance travelled by the dissolved substance (solute) and the distance travelled by the solvent

What is a pure substance?

Something that only contains one compound or element- not mixed with anything else

how can you find out the purity of a substance?

by measuring the boiling or melting point and comparing it to the melting or boiling point of the pure substance

what will a chemically pure substance do?

melt or boil at a specific temperature.

what does it mean if a substance that has been measured for it purity had a close melting or boiling point value as the pure substance?

the substance tested is almost pure (the closer it is, the more pure)

4 things impurities do to substances

lower the melting point, increase the melting range of the substance, increase the boiling point and result in the sample boiling at a range of temperatures

What are formulations?

Useful mixtures with a precise purpose that are made by following a 'formula'

what are paint formulations composed of?

pigment, solvent, binder and additives

what does pigment in paint do?

give the paint colour

what is the solvent in paint used for?

to dissolve the other components and alter viscosity

what does the binder in paint do?

forms a film that holds the pigment in place after it's been painted on

1 example of how formulations are important in the pharmaceutical industry

by altering the formulation of a pill, chemists can make sure it delivers the drug to the correct part of the body at the right concentration, that its consumable and has a long shelf life

7 examples of how formulations are important in every day life

formulations can be found in cleaning products, fuels, cosmetics, fertilisers, metal alloys and food and drink

what tells you a product's formulation?

the information on the packaging that has a ratio or percentage of each component

what is chromatography?

An analytical method used to separate the substances in a mixture

what are the '2 phases' of chromatography?

mobile phase and stationary phase

what is the 'mobile phase' of chromatography?

where the molecules can move, always a liquid or gas

what is the 'stationary phase' of chromatography?

where the molecules can't move, a solid or thick liquid

what happens during a chromatography experiment?

the substances in the sample constantly move between the mobile and stationary phases (an equilibrium is formed)

how is an equilibrium formed between the mobile and stationary phases in chromatography?

the mobile phase moves through the stationary phase, anything dissolved in the mobile phase moves with it

what happens to the chemicals that spend more time in the mobile phase than the stationary phase?

They will move further through the stationary phase

where will the components in a mixture normally separate through?

the stationary phase (as long as all the components spend different amounts of time in the mobile phase)

what will a pure substance form in chromatography experiments?

1 spot in any solvent as there is only one substance in the sample

what is the 'stationary phase' in chromatography?

the chromatography paper

what is the 'mobile phase' in chromatography?

the solvent

what 2 things does the amount of time the molecules spend in each phase depend on in chromatography?

solubility of the molecules and how attracted they are to the paper

how do molecules spend more time in the mobile phase in chromatography?

if the molecules have a higher solubility and are less attracted to the paper, they will be carried further up the paper

how does the Rf value become larger in a chromatogram?

the substance travels further through the stationary phase

how can you calculate Rf values?

distance travelled by substance (B) ÷ distance travelled by solvent (A)

why is chromatography often carried out?

To see if a certain substance is present in a mixture

how do you find out if a certain substance is in a mixture?

run a pure sample of that substance alongside the unknown mixture, and if the Rf values of the reference and one of the spots in the mixture match, the substance may be present

what is the Rf value dependent on?

the solvent (Rf will change if solvent changes)

The 4 common gases

chlorine, oxygen, carbon dioxide and hydrogen

how can you test if chlorine is present?

bleaches damp litmus paper, turning it white

how can you test if oxygen is present?

put a glowing splint inside a test tube containing oxygen, the oxygen will relight the glowing splint

how can you test if carbon dioxide is present?

bubbling carbon dioxide through an aqueous solution of calcium hydroxide (limewater) causes the solution to go cloudy

how can you test if hydrogen is present?

by holding a lit splint at the open end of a test tube containing hydrogen, you will get a squeaky pop