Chemical Analysis: Identifying Ions

Question 1

Lithium flame test result

Answer 1

crimson

Question 2

Sodium flame test result

Answer 2

yellow

Question 2

Potassium flame test result

Answer 2

lilac flame

Question 3

Calcium flame test result

Answer 3

orange/red

Question 4

Copper flame test result

Answer 4

green flame

Question 5

Copper sodium hydroxide test result

Answer 5

blue precipitate

Question 6

Iron (II) sodium hydroxide test result

Answer 6

green precipitate

Question 7

Iron (III) sodium hydroxide test result

Answer 7

brown precipitate

Question 8

Aluminium sodium hydroxide test result

Answer 8

white precipitate, dissolves in excess to form a colourless solution

Question 9

Calcium sodium hydroxide test result

Answer 9

white precipitate

Question 10

Magnesium sodium hydroxide test result

Answer 10

white precipitate

Question 11

Describe the test for carbonate anions.

Answer 11

1. Add dilute acid
2. Fizzing/effervesence observed as CO₂ is released
3. Collect gas and bubble it through limewater
4. Limewater goes cloudy

Question 12

Describe the test for sulfate anions.

Answer 12

1. Add dilute hydrochloric acid
2. Add barium chloride solution.
3. White precipitate forms

Question 13

Describe the test for halide anions.

Answer 13

1. Add dilute nitric acid
2. Add silver nitrate solution

Question 14

What are the results for the halide ion tests?

Answer 14

chloride - white precipitate
bromide - cream precipitate
iodide - pale yellow precipitate

Question 15

Describe how to perform a flame test to identify metal ions.

Answer 15

1. Clean a nichrome wire loop by holding it in a blue flame from a bunsen burner.
2. Dip the loop into the sample you want to test and put it back in the flame.
3. Record the colour of the flame.

Question 16

What are the limitations of doing a flame test?

Answer 16

• only works for samples that contain a single metal ion
• if the sample tested contains a mixture of metal ions then the flame colours of som ions may be masked by the colours of others

Question 17

What are the equations for the halide tests?

Answer 17

Ag⁺_(aq) + Cl^-_(aq) → AgCl_(s)

Ag⁺_(aq) + Br^-_(aq) → AgBr_(s)

Ag⁺_(aq) + I^-_(aq) → AgI_(s)

Question 18

Whats the equation for the sulfate ion test?

Answer 18

Ba²⁺ + SO₄^2-_(aq) → BaSO_4(s)

Question 19

What are the advantages of using flame emission spectroscopy to identify ions?

Answer 19

• very sensitive - they can detect very small amounts of substances
• very fast
• very accurate