Testing gases and ions

Question 1

Testing water practical

Answer 1

1. Set up the apparatus - clamp and stand, thermometer above a beaker containing 50ml of water on top of a bunsen burner
2. Light the bunsen and heat the water
3. Record maximum temperature of steam
4. Put a spatula of anhydrous copper sulfate in a test tube and add 2 drops of water
5. White anhydrous copper sulfate turns blue in the presence of water

Question 2

Testing water purity

Answer 2

Pure water will:
- Boil at 100˚C
- Freeze at 0˚C

Impure water will:
- Boil at over 100˚C
- Freeze at under 0˚C

Question 3

Test for hydrogen

Answer 3

Lit splint produces squeaky pop

Question 4

Test for oxygen

Answer 4

Relights glowing splint

Question 5

Test for chlorine

Answer 5

Damp blue litmus paper turns red then bleaches white

Question 6

Test for ammonia

Answer 6

Turns damp red litmus paper blue

Question 7

Test for carbon dioxide

Answer 7

Turns colourless limewater cloudy

Question 8

Li+ flame test

Answer 8

Red

Question 9

Na+ flame test

Answer 9

Yellow

Question 10

K+ flame test

Answer 10

Lilac

Question 11

Ca2+ flame test

Answer 11

Orange-red

Question 12

Cu2+ flame test

Answer 12

Blue-green

Question 13

Cu2+(aq) cation test

Answer 13

Blue precipitate of Cu(OH)2(s)

Question 14

Fe2+(aq) cation test

Answer 14

Green precipitate of Fe(OH)2(s)

Question 15

Fe3+(aq) cation test

Answer 15

Orange-brown precipitate of Fe(OH)3(s)

Question 16

Al3+(aq) cation test

Answer 16

White precipitate of Al(OH)3(s)

Question 17

Ca2+(aq) cation test

Answer 17

White precipitate of Ca(OH)2(s)

Question 18

Mg2+(aq) cation test

Answer 18

White precipitate of Mg(OH)2(s)

Question 19

NH4+(aq) cation test

Answer 19

No change. Gentle warming produces NH3, which turns damp red litmus paper blue.

Question 20

Lithium chloride anion test

Answer 20

nitric acid + silver nitrate -> white precipitate -> Cl-

Question 21

Sodium bromide anion test

Answer 21

nitric acid + silver nitrate -> cream precipitate -> Br-

Question 22

Potassium iodide anion test

Answer 22

nitric acid + silver nitrate -> yellow precipitate -> I-

Question 23

Ammonium carbonate anion test

Answer 23

HCL into solid salt + limewater -> bubbles of CO2 (limewater cloudy) -> CO32-

Attach bung and delivery tube to test tube with acid and ammonium carbonate and connect with test tube with limewater

Question 24

Aluminium sulfate anion test

Answer 24

Dilute HCL + barium chloride -> white precipitate -> SO42-

Question 25

Calcium carbonate anion test

Answer 25

HCL into solid salt + limewater -> bubbles of CO2 (limewater cloudy) -> CO32-

Attach bung and delivery tube to test tube with acid and calcium carbonate and connect with test tube with limewater

Question 26

Substance used for cation test

Answer 26

Sodium hydroxide solution

Question 27

Substance used for anion test

Answer 27

Halide ions = nitric acid + silver nitrate

Sulfate ions = dilute HCL + barium chloride

Carbonate ions = HCL to the solid salt + limewater

Question 28

Test for ammonium

Answer 28

• add sodium hydroxide to solution containing ammonium ions
• heat solution using bunsen burner
• hold red litmus paper near mouth of test tube
• red litmus paper turns blue in the presence of ammonia gas

Question 29

Test for sulfate ions

Answer 29

• add a few drops of dilute hydrochloric acid
• add a few drops of barium chloride
• if sulfate is present a white precipitate of barium sulfate will form

Question 30

Test for hydroxide ions

Answer 30

Test pH of solution using red litmus paper. The presence of hydroxide ions will turn red litmus paper blue (alkaline)