8.3 Qualitative Analysis

Question 1

What colour flame does lithium produce?

Answer 1

Crimson

Question 2

What colour flame does sodium produce?

Answer 2

Yellow

Question 3

What colour flame does potassium produce?

Answer 3

Lilac

Question 4

What colour flame does calcium produce?

Answer 4

Orange-red

Question 5

What colour flame does copper (Cu2+) produce?

Answer 5

Green

Question 6

How can you test for hydrogen?

Answer 6

Place a lit wooden splint into a test tube containing the gas. You should hear a squeaky pop

Question 7

How can you test for oxygen?

Answer 7

Place a glowing wooden splint into a test tube containing the gas. You should observe the splint being relit

Question 8

How can you test for Carbon Dioxide?

Answer 8

Bubble the gas through limewater. It should turn the limewater cloudy

Question 9

How can you test for Chlorine gas?

Answer 9

Add damp litmus paper to the gas. it should bleach it white

Question 10

What do you use to test for positive metal ions?

Answer 10

Sodium Hydroxide

Question 11

What colour precipitate is produced when Sodium Hydroxide reacts with Al3+ ions?

Answer 11

White

Question 12

What colour precipitate is produced when Sodium Hydroxide reacts with Ca2+ ions?

Answer 12

White

Question 13

What colour precipitate is produced when Sodium Hydroxide reacts with Mg2+ ions?

Answer 13

White

Question 13

What colour precipitate is produced when Sodium Hydroxide reacts with Cu2+ ions?

Answer 13

Blue

Question 14

What colour precipitate is produced when Sodium Hydroxide reacts with Fe2+ ions?

Answer 14

Green

Question 15

What colour precipitate is produced when Sodium Hydroxide reacts with Fe3+ ions?

Answer 15

Brown

Question 16

After testing Magnesium, Calcium and Aluminium ions with Sodium Hydroxide, what should you do to distinguish these ions?

Answer 16

-If excess sodium hydroxide is added, the aluminium hydroxide precipitate dissolves to form a colourless solution
-Calcium flame test, will get an orange-red flame

Question 17

What should you use to test for Carbonate Ions?

Answer 17

An acid

Question 18

Describe how to perform a carbonate ion test.

Answer 18

-Add dilute acid to the solid or solution
-If you see bubbles, the unknown compound could be a carbonate (should be CO2)
-Perform the CO2 test, bubble the gas through limewater, if it turns cloudy then CO2 is present.

Question 19

Describe how to perform a sulfate ion test.

Answer 19

-Add aqueous barium ions to the unknown solution
-The formation of a white precipitate of barium sulfate indicates the presence of sulfate ions

Question 20

What do you use to test for sulfate ions?

Answer 20

Barium Nitrate or Barium Chloride

Question 21

What should you use to test for sulfates in a solution if you intend to test for halides afterwards? Why?

Answer 21

Barium Nitrate, because Barium Chloride adds Cl- ions to the solution

Question 22

What do you use to test for halides?

Answer 22

Aqueous Silver Nitrate

Question 23

Describe how to perform a halide test.

Answer 23

Add aqueous silver nitrate to an aqueous solution of a halide. Silver reacts and forms precipitates of different colours.

Question 24

What colour precipitate forms when Silver Nitrate reacts with Chlorine?

Answer 24

White

Question 25

What colour precipitate forms when Silver Nitrate reacts with Bromine?

Answer 25

Cream

Question 26

What colour precipitate forms when Silver Nitrate reacts with Iodine?

Answer 26

Yellow

Question 27

Describe what should be done if the colour of silver halide precipitates are difficult to tell apart.

Answer 27

-Add aqueous ammonia and test the solubility of the precipitate.

Question 28

Describe the solubility of silver chloride in ammonia.

Answer 28

Soluble in dilute NH3

Question 29

Describe the solubility of silver bromide in ammonia.

Answer 29

Soluble in concentrated NH3

Question 30

Describe the solubility of silver iodide in ammonia.

Answer 30

Insoluble in concentrated NH3

Question 31

List the sequence of the anion tests.

Answer 31

Carbonate test, sulfate test, halides test

Question 32

Why should the carbonate test be performed first?

Answer 32

Because it can be carried out without the possibility of an incorrect conclusion. Neither sulfate nor halides bubble with dilute acid

Question 33

Why should the sulfate test be performed second?

Answer 33

If you carry out a sulfate test on a carbonate, you will get a white precipitate too. So find out if carbonates are present before

Question 34

Why should the halide test be performed third?

Answer 34

Because both carbonate and sulfate ions react with silver to form precipitates, so they will give misleading positive results.

Question 35

If you are asked to analyse a mixture of chemicals in a test tube, should you carry them out in the same solution?

Answer 35

Yes

Question 36

If you are performing several chemical tests on a single solution, what should you do during the carbonate test?

Answer 36

-If you see bubbles, continue adding dilute nitric acid until bubbling stops to remove all CO3 ions -Use Nitric acid instead of sulfuric acid or hydrochloric acid

Question 37

If you are performing several chemical tests on a single solution, what should you do during the sulfate test?

Answer 37

-Use barium nitrate, and filter out later -Do NOT use BaCl2

Question 38

If you are performing several chemical tests on a single solution, what should you do during the halide test?

Answer 38

Can continue as normal, because any carbonate or sulfate ions will have been removed

Question 39

Describe how you would test for ammonium ions.

Answer 39

-Add aqueous sodium hydroxide to the solution -Ammonia gas will be produced -Test the gas with moist pH indicator paper, which will turn the paper blue (alkaline)