Chemical Analysis

Question 1

What is a pure substance?

Answer 1

Made up of just 1 substance (either an element or compound)

Question 2

What are fixed points in an element or compound

Answer 2

Melting and boiling points

Question 3

Pure substances, impurities and mixtures fixed points

Answer 3

Pure substances = have specific temperatures at which they melt and boil
Mixtures = do not have sharp melting and boiling points, state changes over range of temperatures
Impurities = lower the melting point and raise boiling point of substances, size of difference of pure substance is its fixed point. The purer the compound the narrower the melting point range

Question 4

What is a formulation?

Answer 4

Mixture been designed to produce a useful product
Often contain between 5-10% of active drug, with specific compound that affects nobody to cure illness and relieve someone of their symptoms

Question 5

Paint formulations

Answer 5

Pigment
Binder (to wall)
Solvent (spread)

Question 6

Cleaning agents forumlations

Answer 6

Surfactant (removes grease)
Water (squirt easily)
Colouring and fragrance additives
Rinse

Question 7

What does chromatography involve?

Answer 7

Mobile and stationary phase
Mobile = moves through stationary phase carrying components of mixture
Substance with stronger force of attraction to stationary phase will not travel as far

Question 8

What does chromatography tell you?

Answer 8

If mixture if a single compound or mixture
More than one spot = mixture
Single spot = pure substance

Question 9

How to find distance spot travels up paper?

Answer 9

Retention factor = distance moved by substance from base line / distance moves by solvent (from base line to top)

Question 10

How to test for hydrogen

Answer 10

Lighted splint pops

Question 11

Testing for oxygen gas

Answer 11

Glowing splint relights

Question 12

Test for carbon dioxide

Answer 12

Limewater turns milky

Question 13

Test for chlorine

Answer 13

Blue litmus paper turns white

Question 14

Metal ion and flame colour

Answer 14

Lithium = crimson
Sodium = yellow
Potassium = lilac
Calcium = orange-red
Copper = green
Magnesium = no colour

Question 15

How to carry out a flame test

Answer 15

1) Nichrome wire loop dipped in concentrated hydrochloride acid
2) Dipped in acid again before dipping it into metal compound being tested
3) Hold loop in flame of Bunsen Burner
4) Colour identifies metal ion
5) If its a mixture of metal ions, dominant colours can show

Question 16

Metal cation tests with sodium hydroxide

Answer 16

Identify positive ions
Aluminium, calcium and magnesium form white precipitates with sodium hydroxide solution
Ions will not dissolve

Question 17

Test for carbonate equation

Answer 17

CO2 + 2H -> CO2 + H2O

Question 18

Colour of precipitate telling you which halide ion is present

Answer 18

Iodide = yellow
Bromide = cream
Chloride = white

Question 19

How to test halides

Answer 19

Add dilute nitric acid and silver nitrate solution

If a precipitate forms then a halide is present

Question 20

Benefits and disadvantages of instrumental methods

Answer 20

Highly accurate
Quicker
Very small samples

Expensive
Training needed
Interpreted only by comparison with date from known substances

Question 21

What are instrumental methods important for?

Answer 21

Important in work of environmental agencies fighting pollution

Question 22

What do chemists use flame emission spectroscopy for?

Answer 22

Analyse samples for metal ions

Question 23

How is flame emission spectroscopy done?

Answer 23

Sample is heated in flame
Energy provided makes electrons in metal ions jump into higher shells
Fall back into lower shells and their energy is released as light

Question 24

How are wavelengths analysed?

Answer 24

Analysed by passing it through a spectrum
Each metal ion absorbs and gives out its own light spectrum
Light spectrum can be compared

Question 25

Spectrometer

Answer 25

Measured intensity of light with a specific wavelength

Gives a value for unknown concentration