C8 - Chemical Analysis

Question 1

What is a pure substance

Answer 1

a single element or compound, not mixed with any other substance.

Question 2

Describe how boiling/melting point shows how pure a substance is ( 6 marks)

Answer 2

A chemically pure substance will melt/boil at a specific temperature
Measure its boiling/melting point and compare it with the melting/boiling point of the pure substance (from a data book)
Closer measured value is to actual value the purer the sample
Impurities in your sample will lower mp and increase melting range
Impurities in your sample will also increase bp and may result in your sample boiling at a range of temperatures

Question 3

What is formulation

Answer 3

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

Question 4

Describe how formulations are made ( 2 marks)

Answer 4

Formulations are made by mixing the components, in carefully measured quantities to ensure that the product has the required properties

Question 5

Give 7 examples of formulation

Answer 5

fuels, cleaning agents, paints, medicines, alloys, fertilisers and
foods

Question 6

What is chromatography used for

Answer 6

Chromatography can be used to separate mixtures and can give information to help identify substances

Question 7

What is the mobile and stationary phase

Answer 7

Mobile phase - where the molecules can move - always liquid or gas
Stationary phase - where the molecules can’t move - can be solid or really thick liquid

Question 8

What is the Rf equation

Answer 8

distance travelled by substance/distance travelled by solvent

Question 9

Describe how a student can carry out chromatography (6 marks)

Answer 9

Draw line near bottom of a sheet of filter paper - use a pencil as pencil marks are insoluble and won’t dissolve in the solvent
Add a spot of ink to the link and place the sheet in a beaker of solvent e.g water
Make sure ink isn’t touching the solvent - so it doesn’t dissolve it
Place lid on top of the container to stop the solvent evaporating
Solvent seeps up the paper carrying the ink with it
Each different dye in the ink will move up the paper at a different rate so the dyes will separate
If the dyes in the ink are insoluble - stays on baseline
When solvent has nearly reached the top of the paper, take the paper out of the beaker and leave it to dry

Question 10

Test for:
chlorine
oxygen

Answer 10

Chlorine bleaches DAMP litmus paper turning it white
Glowing splint inside a test tube containing oxygen, oxygen will relight glowing splint

Question 11

Test for:
carbon dioxide
hydrogen

Answer 11

Bubbling carbon dioxide through an aqueous solution of calcium hydroxide (limewater) - causes solution to turn cloudy
Holding a lit splint at the open end of a test tube containing hydrogen will result in a squeaky pop