chemical analysis

what do we call a substance that is made of a single element or compound, not mixed with any other substance

what do we call a substance that is made of a single element or compound, not mixed with any other substance

pure

what do we know about the boiling point of pure elements

it is at a specific temperature

what do we call a mixture that has designed as a useful product

formulation

give the names of some common formulations

• fuels

• cleaning agents

• paints

• medicines

• alloys

• fertiliser

• foods

which process can be used to separate mixtures and identify substances

chromatography

what are the two phases involved in chromatography

• mobile phase

• stationary phase

what do we call the ratio of the distance moved by a compound to the distance moved by the solvent

the rf value

what is the formula to work out the Rf value

distance moved by substance ÷ distance moved by solvent

what values can the Rf take

any value between 0 and 1

in chromatography what will a pure compound produce

a single spot

what does the separation of substances in chromatography depend on

the distribution of substances between the mobile and stationary phase

what gas test uses a burning splint held at the open of a test tube of a gas

hydrogen test

which gas test uses a glowing splint inserted into a test tube of the gas

oxygen test

what will happen if hydrogen is present in a gas test

a lit splint will burn rapidly with a pop sound

what will happen if oxygen is present in a gas test

the glowing splint will relight

what is limewater

an aqueous solution of calcium hydroxide

what colour does limewater turn in the present of carbon dioxide

milky (cloudy)

what gas are you testing for if you bubble the gas thought an aqueous solution of calcium hydroxide

carbon dioxide

what do you need to use to test for chlorine

litmus paper

when damp litmus paper is put into chlorine gas what happens

it bleaches and turns white

what can be flame test be used to identify

metal ions (cations)

if lithium compound is present, what would be the colour of the flame

crimson

if sodium compound is present, what would be the colour of the flame

yellow

if potassium compound is present, what would be the colour of the flame

lilac

if calcium compound is present, what would be the colour of the flame

orange-red

if copper compound is present, what would be the colour of the flame

green

what happens to some flame colours if it contains a mixture

it can be masked

how do you carry out a flame test

1. dip in a nichrome wire in hydrochloric acid and heat to clean

2. dip into the metal compound then hold in the roaring blue flame

3. using the colour of the Bunsen burner to identify the metal compound

what is used to identify metal hydroxide

sodium hydroxide

what does the solution of aluminium ions form (Al³⁺)

• forms a white precipitate

• dissolves in excess sodium hydroxide solution

what does the solution of calcium ions form (Ca²⁺)

• forms a white precipitate

• doesn’t dissolves in excess sodium hydroxide solution

what does the solution of magnesium ions form (Mg²⁺)

• forms a white precipitate

• doesn’t dissolves in excess sodium hydroxide solution

what does the solution of copper ions form (Cu²⁺)

forms a blue precipitate

what does the solution of iron (II) ions form (Fe²⁺)

forms a green precipitate

what does the solution of iron (III) ions form (Fe³⁺)

forms a brown precipitate

balanced equation for aluminium ions

Al³⁺ (aq) + 3OH- (aq) → Al(OH)₃

balanced equation for calcium ions

Ca²⁺ (aq) + 2OH- (aq) → Ca(OH)₂ (s)

balanced equation for magnesium ions

Mg²⁺ (aq) + 2OH- (aq) → Mg(OH)₂ (s)

balanced equation for copper II ions

Cu²⁺ (aq) + 2OH- (aq) → Cu(OH)₂ (s)

balanced equation for iron II ions

Fe²⁺ (aq) + 2OH- (aq) → Fe(OH)₂ (s)

balanced equation for iron III ions

Fe³⁺ (aq) + 2OH- (aq) → Fe(OH)₃ (s)

what does the reaction of carbonates and dilute acids form

carbon dioxide

how can carbon dioxide can be identified

limewater

what does halide ions in solution produce

precipitates with silver nitrate solution in the presence of dilute nitric acid

what does silver chloride produce

a white precipitate

what does silver bromide produce

a cream precipitate

what does silver iodide produce

a yellow precipitate

what do sulfates ions produce

a white precipitate with barium chloride solution in the presence of dilute hydrochloric acid

what are instrumental methods advantages

• accurate

• rapid

• sensitive

what are instrumental method disadvantage

• usually expensive

• requires special training to use

• give results that can be interpreted only by comparison with known substances

what is an example of an instrumental method

flame emission spectroscopy

how is a flame emission spectroscopy used

the sample is put into a flame and the light given out is passed through a spectroscope. the output is called a line spectrum

advantage of flame test

• Simple equipment

• Quick result

• Very small amount of sample required

disadvantage of flame test

• Difficult to analyse mixtures

• One colour may mask others

• Subjective