Analysing Substances

Method

Solid Test: Take a nichrome wire and dip it in hydrochloric acid. Place the wire in a roaring flame to clean the wire. Dip this in a powdered form of the metal ion and place that in the roaring flame. Observe the colour change.

Liquid Test: Take a wooden splint and soak it in a solution form of the metal ion. Place this in a roaring flame. Observe the colour change.

Results 

Potassium- Lilac

Sodium- Yellow

Lithium- Crimson

Barium- Green

Calcium-Brick Red

Copper (II)- Green

Why do the ions give off different colours?

When heated the electrons move up an electron shell, on returning to their own level they give of energy, in this case light energy.

Method

Take a test tube and fill it with 1 cm depth of a named solution, add an equal amount of alkali (NaOH) and leave to sit in a test tube rack. Record the results.

Copper (II)- Blue Precipitate

Iron(II)- Green Precipitate

Iron(III)- Brown Precipitate

Aluminium- White Precipitate (dissolves when excess hydrochloric acid is added)

Magnesium- White Precipitate

Calcium- White Precipitate

Barium- White Precipitate

Presipitate= insoluble solid

Al, Cl, Mg all produce white precipitates. + excess NaOH

Al will redissolve, Ca and Mg will have no change, do flame test to tell them apart.

Add 1cm depth of the solution to test tube

Add 1cm deoth of hydrochloric acid.

If it effervesces take a pippet and extract some of the gas.

Add this to limewater. If it turns cloudy then it is a carbonate ion.

2H+(aq)+CO 3-(aq)→CO2(g)+H2O(l)

Add 1cm depth of the solution to test tube.

Add 1cm depth of dil hydrochloric adic.

Add 1cm depth of barium chloride.

If it turns cloudy or a white precipitate is formed it is Barium sulphate.

Ba 2+ (aq)+SO4 2- (aq)→BaSO4(s)

Add 1cm depth of the solution to a test tube.

Add 1cm depth of dil nitric acid.

Add 1cm depth of silver nitrate solution.

Halide’s will form a precipate.

Chloride-  Cl-   white precipitate   Ag + (aq) + Cl - (aq) →AgCl(s)

Iodide-  I-   yellow precipitate   Ag + (aq) + I - (aq) →AgI(s)

Bromide-  Br-   cream precipitate   Ag + (aq) + Br - (aq) →AgBr(s)

A mixture: two or more elements or compounds are mixed together but not chemically combined

Filtration- insoluble solid and a liquid, eg. sand and water

Evaporation and Crystalisation- soluble solid and liquid, eg, salt and water

Distilation or Chromatography- two liquids, eg. ink and water

• The solution is heated in a round bottom flask.
• Because the ethanol, ink and the water have different boiling points they will evaportate at different times.
• Ethanol evaporates first.
• The ethanol evaporates rising up the flask in the leibig condenser.
• Cool water runs through the condenser, condensing the ethanol.
• The liquid drips into the conical flask at the end of the condenser.
• The conical flask is changed and the cycle continues

It is used for separating soluble liquids and compounds to identify the liquids.

Method

Take some chromatography paper and put dots of food colouring at the bottom.

Place these in a beaker of water, making sure the dots aren’t in the water.

Leave and allow the water to be absorbed into the paper.

Some liquids are more soluble than others and will travel further up the paper. This is how they can be distinguished.

Using Rf values to distinguish liquids

Rentention factor. Rf values are used to identify substances and are unique to each substance in a given solvent. Is a ratio.

Rf = distance spot travels/distance solvent travels