C8 (not tests for gases)

Question 1

what does “pure” mean in non-scientific terms?

Answer 1

usually when you refer to a substance being pure you mean that nothing has been added to it, so it’s in its natural state. For example: pure milk or beeswax

Question 2

what is a pure substance in scientific terms?

Answer 2

in chemistry, a pure substance is something that only contains one compound or element throughout - not mixed with anything else

Question 3

how can you test how pure a substance is?

Answer 3

1. a chemically pure substance will melt or boil at a specific temperature
2. you can test the purity of a sample by measuring its melting or boiling point and comparing it with the melting or boiling point of the pure substance (which you can find from a data book)
3. the closer your measured value is to the actual melting or boiling point, the purer your sample is
4. Impurities in your sample will lower the melting point and increase the melting range of your substance
5. impurities in your sample will also increase the boiling point and may result in your sample boiling at a range of temperatures

Question 4

what are formulations?

Answer 4

useful mixtures with a precise purpose that are made by following a ‘formula’ (a recipe). Each component in a formulation is present in a measured quantity, and contributes to the properties of the formulation so that it meets its required function

Question 5

give an example of a formulation, and describe what it is composed of

Answer 5

paints are formulations composed of:
- pigment - gives the paint colour, for example titanium oxide is used as a pigment in white paints
- solvent - used to dissolve the other components and alter the viscosity
- binder (resin) - forms a film that holds the pigment in place after it’s been painted on
- additives - added to further change the physical and chemical properties of the paint.
Depending on the purpose of the paint, the chemicals used and their amounts will be changed so the paint produced is right for the job

Question 6

which industry are formulations really important for? why?

Answer 6

formulations are really important in the pharmaceutical industry. For example, 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 it’s consumable and has a long enough shelf life

Question 7

give 6 examples of where formulations can be found in everyday life

Answer 7

1. cleaning products
2. fuels
3. cosmetics
4. fertilisers
5. metal alloys
6. food + drink

Question 8

how can you (usually) find out information about a product’s formulation when you buy a product?

Answer 8

when you buy a product, you might find that it has information about its composition on the packaging. For example, the ratio or percentage of each component. This tells you the product’s formulation. It also lets you choose a formulation with the right composition for your particular use.

Question 9

what is chromatography?

Answer 9

an analytical method used to separate the substances in a mixture. You can then use it to identify the substance.

Question 10

what are the two phases of chromatography?

Answer 10

there are different types of chromatography, but they all have two ‘phases’:

• a mobile phase - where the molecules can move. This is always a liquid or gas
• a stationary phase - where the molecules can’t move. This can be a solid or a really thick liquid

Question 11

what is the interaction between the two phases like in chromatography?

Answer 11

1. during a chromatography experiment, the substances in the sample constantly move between the mobile and the stationary phases - an equilibrium is formed between the two phases
2. the mobile phase moves through the stationary phase, and anything dissolved in the mobile phase moves with it.

Question 12

in chromatography, what does the speed the chemical moves at depend on?

Answer 12

on how it’s ‘distributed’ between the two phases - whether it spends more time in the mobile phase or the stationary phase:
- the chemicals that spend more time in the mobile phase than the stationary phase will move further through the stationary phase

Question 13

how/why do parts of a mixture separate in chromatography?

Answer 13

the components in a mixture will normally separate through the stationary phase, so long as all the components spend different amounts of time in the mobile phase. The number of spots may change in different solvents as the distribution of the chemical will change depending on the solvent. A pure substance will only ever form one spot in any solvent as there is only one substance in the sample