Chemical Analysis

What is a pure substance?

- made up of one substance either an element or a compound

- m.p and b.p are fixed points and can help identify if a substance is pure

How do you recognise an impurity?

- they can lower m.p and raise b.p of a substance as well as increase the temperature range of these changes

What are formulations?

- mixtures designed to make a useful product

What is the mobile phase in chromatography?

The solvent

What is the stationary phase?

The paper

What is the test for hydrogen?

A lit split is held to it, it burns with a squeaky pop

What is the test for oxygen?

- relights with a glowing splint

What is the test for carbon dioxide?

It turns limewater milky when bubbled through it

What is the test for chlorine?

It bleaches damp litmus paper white

How do you carry out the flame tests?

- dip in chrome wire into HCl acid then heat in Bunsen burner to clean

- dip again into acid and then into metal compound

- hold the loop with the sample in the roaring blue flame of a Bunsen burners and note the colour

What colour is the Lithium flame test?

Crimson

What colour is the Sodium flame test?

Yellow

What colour is the Potassium flame test?

Lilac

What colour is the calcium flame test?

Orange-red

What colour is the copper flame test?

Green

What is the test for metal hydroxide ions?

Some metal hydroxides are insoluble and form coloured precipitates when their salts are reacted with sodium hydroxide

What is the test for Magnesium + equation?

White precipitate

Mg2+ (aq) + 2OH-(aq) —> Mg(OH)2 (s)

What is the test for calcium?

White precipitate

Ca2+ (aq) + 2OH- (aq) —-> Ca(OH)2(s)

What is the test for Aluminium?

White precipitate, but goes colourless and displaces when NaOH is in excess

Al3+(aq) = 3OH- —-> Al(OH)3(s)

What is the test for Copper when sodium hydroxide solution is added?

Blue precipitate

Cu2+(aq) + 2OH-(aq) —> Cu(OH)2 (s)

CuCl2 + 2NaOH -> Cu(OH)2 + 2NaCl

What is the test for Iron 2 when added to sodium hydroxide solution?

Green precipitate

Fe2+(aq) + 2OH-(aq) —> Fe(OH)2(s)

FeCl2 + 2NaOH -> Fe(OH)2 + 2NaCl

What is the test for Iron 3 when added to sodium hydroxide solution?

Brown precipitate

Fe3+(aq) + 3OH-(aq) —> Fe(OH)3(s)

FeCl3 + 3NaOH -> Fe(OH)3 + 3NaCl

How do you carry out the carbonates test?

Add dilute acid and you will see effervescence.

If you collect this gas and bubble it through limewater it will go cloudy showing CO2 is present.

What is the equation for the carbonates test?

2H+(aq) + CO3- (s) —> H2O(l) + CO2 (g)

What is the test for sulphates?

Add barium chloride solution and you get a white precipitate of Barium sulfate in the prescience dilute hydrochloride acid

What is the equation for the sulphates test?

Ba2+ (aq) + SO4 2- (aq) —> BaSO4 (s)

BaCl2 + Na2SO4 -> BaSO4 + 2NaCl

What do Halide ions form?

Halide ions form precipitates with silver ions

Ag+(aq) + X- (aq) —> AgX (s)

How do you carry out the halides test?

You first add dilute nitric acid (to remove impurities and carbonate ions that may form) and then you add AgNO3 silver nitrate and observing the precipitate

What is the test for chlorine ions? ANION TEST

White precipitate (silver chloride)

Ag+ (aq) + Cl- (aq) —> AgCl(s)

NaCl + AgNO3 -> AgCl + NaCl

What is the test for bromine ions? ANION TEST

Cream precipitate (silver bromide)

Ag+(aq) + Br-(aq) —> AgBr(s)

NaBr + AgNO3 -> AgBr + NaCl

What is the test for iodine ions? ANION TEST

Yellow precipitate (silver iodide)

Ag+ (aq) + I- (aq) —> AgI(s)

NaI + AgNO3 -> AgI + NaCl

How does flame emission spectroscopy work?

The sample is put into a flame and the light given out is passed through a spectroscope. The output is a line spectrum that can be analysed to identify the metal ions in the solution and measure their concentrations.

Advantages of flame emission spectroscopy

- accurate

- sensitive

- rapid

What is the desire level of solubility and attraction to the paper for the dye to travel furthest up the chromatogram?

Molecules with a higher solubility in the solvent, and which are less attracted to the paper, will spend more time in the mobile phase - and they'll be carried further up the paper.

What is the Rf value dependent on?

It is dependent on the solvent