Identification of Ions

Question 1

Method for flame test

Answer 1

1. get a nichrome wire mounted in handle and dip it into hydrochloric acid and then hold it in the blue flame of the Bunsen. This is to clean the wire.
2. Dip the loop of wire into the solid/solution to be tested and place it into the blue flame of the bunsen
3. record the colour of the flame
4. repeat for the other solutions, ensuring you clean the wire after each test
5. Compare results and see which substances have the same coloured flame

Question 2

Why do we clean the loop

Answer 2

To make sure the wire is not contaminated with other ions from previous tests

Question 3

What are the problems when using flame tests to identify metal ions

Answer 3

Colour of the flame test can be difficult to distinguish if there is only a low concentration of the compound

Sometimes if you have a mixture of metal ions, it can mask the colour of the flame

Question 4

Test for aluminium, calcium, magesium, copper, iron II, iron III in a substance

Answer 4

1. pour 1cm3 of each solution in a test tube
2. Add an equal volume of sodium hydroxide in each test tube
3. place your finger over the top of the test tube and shake gently to mix the solutions
4. a precipitate should form and record your observations

Question 5

Results for test for Aluminium, calcium and magnesium ions

Answer 5

White precipitate
If you add excess sodium hydroxide, the precipitate for aluminium will redissolve

Question 6

result for test for
Copper II
Iron II
Iron III

Answer 6

Blue precipitate
Green precipitate
Brown precipitate

Question 7

Flame test results for:
Lithium
Sodium
Potassium
Calcium
Copper

Answer 7

Li: Crimson flame
Na: yellow flame
K: lilac flame
Ca: orange-red flame
Cu: Green flame

Question 8

Carbonate test

Answer 8

1. pour 2cm3 of limewater into a test tube
2. put 1cm3 of dilute hydrochloric acid to the unknown solution
3. if you see bubbles/effervescence, transfer the gas produced to the limewater using a delivery tube
4. limewater goes cloudy and bubbles are produced if carbonate ions are present

Question 9

Sulphate ion test

Answer 9

1. pour 1cm3 of the solution into a test tube
2. add 1cm3 of dilute hydrochloric acid to the solution
3. add 1cm3 of barium chloride solution
4. white precipitate is formed if sulphate ions are produced

Question 10

Halide ion test

Answer 10

1. add some dilute nitric acid to the unknown solution in a test tube
2. add 1cm3 of silver nitrate solution to the test tube and shake gently to mix

Question 11

Halide ion results
Chloride
Bromide
Iodide

Answer 11

Cl: white precipitate
Br: cream precipitate
I: yellow precipitate

Question 12

Advantages of instrumental methods

Answer 12

• more sensitive - only require a small amount of the substance
• much quicker
• highly accurate

Question 13

disadvantages of instrumental methods

Answer 13

• usually expensive
• takes special training to use
• give results that can often be interpreted only by comparison with data from known substances

Question 14

advantages of chemical tests

Answer 14

cheap

Question 15

disadvantages of chemical tests

Answer 15

less accurate - colours masked in mixtures of ions
Less sensitive - won’t detect small concentrations of ions

Question 16

uses of instrumental methods of analysis

Answer 16

• analysing blood, urine and tissue samples
• analysing the purity of medicines
• analysing the quality of water and air
• analyse the contents of food

Question 17

What is flame emission spectroscopy used for

Answer 17

• identifying metal ions in a solution
• measuring the concentration of metal ions in solution

Question 18

How does flame emission spectroscopy work? ( as in reading results)

Answer 18

Each ion produces a line spectrum which contains specific wavelengths of light

The lines are characteristic of that particular ion, so it can be identified
The concentration of the ions can be found by the intensities of the lines