Chemical Tests

Question 1

What is the test for Halides?
(Chlorine, Bromine, Iodine)

Answer 1

Silver (Ag) Nitrate Test
- dissolve the sample in water
- add nitric acid (prevent false positives)
- add silver nitrate

Cl - white
Br - cream
l - Yellow

Question 2

What is test for carbonate?

Answer 2

• Add hydrochloric acid, look for effervescence
• If there is effervescence, bubble through limewater
• Carbonate is present if gas turns limewater cloudy

Question 3

What is the test for Sulphate?

Answer 3

• add hydrochloric acid, look for effervescence
• if there is no effervescence add barium chloride solution
• if sulphate ions are present a white precipitate forms with Barium ions

Question 4

What is the test for Hydrogen?

Answer 4

Lit splint
Hydrogen = squeaky pop

Question 5

What is the test for Oxygen?

Answer 5

Glowing splinter relights in the presence of oxygen

Question 6

What is the test for water?

Answer 6

Add anhydrous copper sulphate
Observe colour change from white to blue

Question 7

Test for chlorine

Answer 7

Damp blue litmus paper turns white

Question 8

Test for Ammonia Gas

Answer 8

Red litmus paper turns blue

Question 9

How do you test for Cations?
(Flame test)

Answer 9

1. Dip nichrome wire in Hydrochloric acid to clean it
2. Dip wire in sample
3. Hold wire in non luminous Bunsen burner (blue flame - to identify colour change)

Question 10

What are the results for the flame tests?

Answer 10

Li - Red
Na - Yellow
K - Lilac
Ca - Red/Orange
Cu - Blue/green

Question 11

What is the test for ammonium?

Answer 11

1. Dissolve sample in water
2. Add sodium Hydroxide (NaOH) and warm it
3. Test the gas for ammonia - red litmus paper turns blue

Question 12

How do you test for Cu, Fe²+, Fe3+

Answer 12

1. Dissolve sample in water
2. Add sodium Hydroxide

Results:
Copper = Blue
Iron (ll) = Green
Iron (III) = Brown

Question 13

What are the three types of Cation tests?
Cations - positive ions

Answer 13

1. Flame tests - Li, Na, K, Ca, Cu
2. Sodium Hydroxide test - Cu, Fe (ll), Fe (lll)
3. Ammonia test - NH4

Question 14

What are the three types of anion tests?
Anions - negative ions

Answer 14

1. Halides using nitric acid & sliver nitrate - Cl, Br, I
2. Carbonates - CO3 ²-
3. Sulphate using HCl and Barium chloride - SO4 ²-

Question 15

How do you calculate Rf Value?

Answer 15

Distance travelled by dye/Solvent front

Question 16

method for chromatography

Answer 16

1. Draw a start line in pencil on chromatography paper
2. Add spots of different dyes along the line at regular intervals
3. Place paper into a beaker of solvent - solvent must be below pencil line
4. Allow solvent to move up paper
5. Mark out where solvent has reached - solved front
6. Remove paper from beaker and allow to dry

Question 17

Why is nitric acid added when testing Halides?

Answer 17

To remove ions that might also produce a precipitate
To prevent a false positive