Identifying Ions

Question 1

Some metal ions can be identified using flame tests:

Answer 1

Lithium ions = crimson flame

Sodium ions = yellow flame

Potassium ions = lilac flame

Calcium ions = orange red flame

Cooper ions = Green flame

Question 2

Formation of precipitates

Answer 2

React ions with sodium hydroxide solution. It produces insoluble salts called precipitates

Calcium ions form White precipitate calcium hydroxide

Magnesium ions form White precipitate magnesium hydroxide

Aluminium ions form White precipitate aluminium hydroxide. Unlike the other 2 aluminium hydroxide can be dissolved on excess sodium hydroxide liquid producing a colourless solution

Copper 2 ions form blue precipitate copper 2 hydroxide

Iron 2 ions form green precipitate iron 2 hydroxide

Iron 3 ions form brown precipitate Iron 3 hydroxide

Question 3

Testing for presence of carbonates

Answer 3

When carbonates react with dilute acids they form a salt co2 and water.

Therefore you can use the test for co2 to work out of an unknown substance is a carbonate

Bubble gass through limewater and if it turns cloudy there’s a carbonate

Question 4

What are halides

Answer 4

Compounds containing ions of halogen atoms

Question 5

Testing for halides

Answer 5

Add dilute nitric acid to unknown solution
This removes carbonate ions that could disruption test results

Add silver nitrate to same solution. If the halide ions are present they will form a precipitate with the silver ions

Which halogen is it?
Silver chloride is white
Silver bromide is cream
Silver iodide is pail yellow

Question 6

Testing for sulphates

Answer 6

Add dilute hydrochloric acid to remove carbonate ions that could disrupt test results

Add barium chloride to same solution.
If sulphates are present the white precipitate barium sulphate will form

Question 7

Advantages of instrumental methods ( using new teck) for chemical analysis compared to traditional methods

Answer 7

Advantages:
Greater sensitivity and accuracy
Quicker at producing results
Able to analyse tiny samples

Disadvantages:
Instruments are often expensive
Need specific training to operate the instruments
Results often only useful when compared to data from known substances

Question 8

Flame emission spectroscopy advantages and disadvantages compared to traditional methods

Answer 8

Instrumental method of identifying metal ions in a solution and there concentrations

Advantages
More sensitive and accurate
Quicker to produce results
Able to analyse small samples

Disadvantages
Instruments often expensive
Need specific training to operate it
Results often ony useful when compared to data from known substances

Question 9

Spectroscopy process

Answer 9

Place sample of metal solution into flame

The light emitted is captured by the spectroscope which can distinguish between wavelengths of light to produce a line spectrum

We can analyse the line spectra produced to see which metal ions are present

Each metal ion will generate a distinct line spectrum

The intensity of the line spectra gives info about the concentration of the ion