C8 Chemical Analysis

Question 1

Pure substance

Answer 1

A single element of compound not mixed with any other substance

Question 2

Mixture

Answer 2

Consists of 2 or more elements of compounds not chemically combined together. The chemical properties of each substance in the mixture is unchanged

Question 3

Separation processes

Answer 3

Filtration
Crystallisation 
Distillation
Fractional distillation 
Chromatography

Question 4

Pure and impure substances

Answer 4

Boiling and melting point used to see if it is pre or not
Impure substances will have a lower melting point and melt over a broad range of temperatures
Pure substances it will melt more sharply at a specific temperature
Impure boiling point is higher than pure substance

Question 5

Formulation

Answer 5

Is a mixture that has been designed as a useful product

Eg. Paints, alloys, fertilisers and food like ketchup

Question 6

Purpose of component chemicals

Answer 6

To improve the quality of a product
Making an alloy
Adding different amounts of nutrients to make the fertiliser the most effective
Many products are complex mixtures in which each chemical has a particular purpose

Question 7

What’s in a tablet?

Answer 7

The active ingredient may be very small but it may be difficult to take into the body. Added to a filler that bulks up the product to sensible size and a lubricant is added so tablets can be taken easily

Question 8

Chromatography

Answer 8

Water separated dyes as it rises up the chromatography paper

Question 9

Stationary phases

Answer 9

When the solvent didn’t move

Question 10

Mobile phase

Answer 10

When water and dyes moved

Question 11

Rf values

Answer 11

Distance moved by substance/distance moved by solvent

This is the ratio moved by a compound (from the origin to the centre of the spot) to the distance moved by the solvent

Question 12

Assessing purity of drugs

Answer 12

Impure substances will separate

Pure substance will stay the same

Question 13

RP: investigate how paper chromatography can be used in forensic science to identify an ink mixture used in forgery

Answer 13

Draw pencil line on litmus paper, put spots of different solvent on the line. Once solvent dry place paper in water below the pencil line and wait for them to separate
Once separate let paper dry then work out the Rf value

Question 14

Hydrogen test

Answer 14

Squeaky pop

Question 15

Oxygen test

Answer 15

Relighting a glowing splint

Question 16

Carbon dioxide test

Answer 16

Limewater turns from colourless to milky white when carbon dioxide is bubbled through it

Question 17

Chlorine test

Answer 17

Damp litmus paper is bleached

Question 18

Producing flame colours

Answer 18

Wear goggles 
Clean wire with HCl and hold in blue flame
Moisten a flame test wire with HCl
Dip wire into sample solid chemical
Hold flame test wire in blue flame
Record colour of flame

Question 19

Flame colours

Answer 19

Lithium Crimson
Calcium orange red
Sodium yellow
Copper green
Potassium lilac

Question 20

Identifying substances

Answer 20

Flame tests can be used to identify cations in compounds

Question 21

Coloured precipitates

Answer 21

A compound which contains a transition metal is often coloured
If sodium hydroxide solution is added to these precipitates form different colours

Question 22

White precipitates

Answer 22

Sodium hydroxide solution also forms precipitates with other metal ions such as magnesium, calcium and aluminium

Question 23

Reactions of carbonates

Answer 23

White carbonates if from group 1 or 2
Form colour carbonates if transition metal
React with acids to form CO2 which turns limewater milky

Question 24

Testing for Halides

Answer 24

Test d using silver nitrate

Question 25

Testing for sulfates

Answer 25

Tested using Barium chloride

Question 26

To identify single ions

Answer 26

Test for gases
Flame test
Precipitate tests with sodium hydroxide, barium chloride, silver nitrate

Question 27

RP: use chemical tests to identify the ions in unknown singe ionic compounds

Answer 27

Flame test 
Precipitation with sodium hydroxide
Testing for CO2
Testing with silver nitrate
Testing with barium chloride 
Identify cation and anion from from these results to find the compound

Question 28

Advantages of instrumental techniques

Answer 28

More: rapid,accurate,sensitive

Spectroscopy, electrochemical analysis, separation techniques

Question 29

How do instrument methods work?

Answer 29

Stimulus: light, heat,current,voltage
Sample
Input transducer (detector) 
Signal processor: amplifier, digitzer
Readout: meter,plotter,computer

Question 30

Flame emission spectroscopy

Answer 30

Instrumental method
Analyses ions in solution
Sample put into flame and light given out is passed through a spectroscope
The output is a line spectrum

Question 31

Advantage of flame emission spectra

Answer 31

Can identify all ions in compounds