Topic 8 - Chemical analysis

Question 1

Method for chromatography

Answer 1

-Pencil baseline with a ruler and put drop of the ink(preferably ink with many substances) on the baseline
-fill beaker with solvent - water or ethanol up shallow just under the baseline
-dip chromatography paper and hold it upright using tape or a stick
-lid optional to stop solvent evapourating
-leave to dry

Question 2

What is the mobile and stationary phase in paper chromatography

Answer 2

The mobile phase is the ink/dye and the stationary phase is the paper or very thick liquid

Question 3

what can you know from how far a certain ink moves up the paper

Answer 3

More soluble substances move further up the paper

Question 4

What is the equation for the RF value

Answer 4

Distance travelled by the substance / distance travelled by the solvent
Measure up to the top of the solvent and measure up to the middle of the points

Question 5

The test for chlorine

Answer 5

When damp litmus paper is put into chlorine gas the litmus paper is bleached and turns white.

Question 6

Test to identify halides

Answer 6

First add dilute nitric acid then add silver nitrate solution
Results - Silver chloride is white, silver bromide is cream and silver iodide is yellow coloured precipitate produced

Question 7

How to carry out flame test

Answer 7

1. Clean a wire loop using HCL
2. Hold it in the blue flame until it burns without colour
3. Dip the loop into the sample then Place the loop in the flame ,record the colour

Question 8

Tests for metal ions (cations)- positive charge

Answer 8

add sodium hydroxide to metal ion then if its coloured precipitate then either :
Light Blue for copper II
“dirty “ green for Iron II
or reddish brown for iron III
If its White precipitate - Aluminium calcium or magnesium , only aluminium dissolves

Question 9

Testing for sulphates -

Answer 9

Add Dilute HCL then if fizzing / CO2 produced = carbonate
or for a sulfate , add HCl then add barium chloride and white precipitate shows sulphates present

Question 10

what is a formulation

Answer 10

A formulation is a mixture that has been designed as a useful product.
Formulations include fuels, cleaning agents, paints, medicines, alloys, fertilisers and foods.

Question 11

flame tests

Answer 11

-Lithium compounds result in a Crimson flame
-Sodium compounds result in a Yellow flame
-Potassium compounds result in a lilac flame
-Calcium compounds result in an orange-red flame
-Copper compounds result in a green flame.

Question 12

advantages of instrumental methods compared with the chemical tests

Answer 12

speed
accuracy - they reliability measure
sensitive - they can detect very small amounts of substances in a sample