Tests for ions and Gasas

Question 1

How can metal ions be detected?

Answer 1

Metal ions can be detected using flame tests.

Question 2

What is the purpose of dipping nichrome wire in hydrochloric acid?

Answer 2

To remove impurities.

Question 3

What should you observe when holding the sample in a roaring Bunsen flame?

Answer 3

Observe the flame colour in the first few seconds.

Question 4

What flame colour does Lithium (Li+) produce?

Answer 4

Red.

Question 5

What flame colour does Sodium (Na+) produce?

Answer 5

Yellow.

Question 6

What flame colour does Potassium (K+) produce?

Answer 6

Lilac.

Question 7

What flame colour does Calcium (Ca2+) produce?

Answer 7

Orange-red.

Question 8

What flame colour does Copper (Cu2+) produce?

Answer 8

Blue-green.

Question 9

What happens when metal ions react with Sodium Hydroxide (NaOH)?

Answer 9

They form a coloured precipitate.

Question 10

What is the colour of the precipitate for Copper (II) (Cu2+)?

Answer 10

Blue.

Question 11

What is the chemical equation for Copper (II) precipitate formation?

Answer 11

Cu2+ (aq) + 2OH- (aq) 🡪 Cu(OH)2 (s).

Question 12

What is the colour of the precipitate for Iron (II) (Fe2+)?

Answer 12

Green.

Question 13

What is the chemical equation for Iron (II) precipitate formation?

Answer 13

Fe2+ (aq) + 2OH- (aq) 🡪 Fe(OH)2 (s).

Question 14

What is the colour of the precipitate for Iron (III) (Fe3+)?

Answer 14

Brown.

Question 15

What is the chemical equation for Iron (III) precipitate formation?

Answer 15

Fe3+ (aq) + 2OH- (aq) 🡪 Fe(OH)3 (s).

Question 16

How can Ammonium ion (NH4+) be detected?

Answer 16

By adding sodium hydroxide solution, which releases ammonia.

Question 17

What happens to damp red litmus paper when ammonia is produced?

Answer 17

It turns blue.

Question 18

What test is used for Carbonates (CO3 2-)?

Answer 18

Add Hydrochloric acid and test for Carbon dioxide.

Question 19

What indicates the presence of Carbon dioxide in the carbonate test?

Answer 19

Bubbling through limewater which turns milky.

Question 20

What test is used for Sulphates (SO42-)?

Answer 20

Add Hydrochloric acid, then Barium Chloride to see a white precipitate.

Question 21

What is the chemical equation for Sulphate precipitate formation?

Answer 21

Ba2+ (aq) + SO42- (aq) 🡪 BaSO4 (s).

Question 22

What test is used for Halides (Cl-, Br-, I-)?

Answer 22

Add nitric acid then Silver Nitrate.

Question 23

What is the result for Chloride (Cl-) in the halide test?

Answer 23

White precipitate.

Question 24

What is the chemical equation for Chloride precipitate formation?

Answer 24

Cl- (aq) + Ag+ (aq) 🡪 AgCl (s).

Question 25

What is the result for Bromide (Br-) in the halide test?

Answer 25

Cream precipitate.

Question 26

What is the chemical equation for Bromide precipitate formation?

Answer 26

Br- (aq) + Ag+ (aq) 🡪 AgBr (s).

Question 27

What is the result for Iodide (I-) in the halide test?

Answer 27

Yellow precipitate.

Question 28

What is the chemical equation for Iodide precipitate formation?

Answer 28

I- (aq) + Ag+ (aq) 🡪 AgI (s).

Question 29

What is the test for Oxygen gas?

Answer 29

It relights a glowing splint.

Question 30

What is the test for Hydrogen gas?

Answer 30

A squeaky pop with a lighted splint.

Question 31

What is the test for Carbon Dioxide?

Answer 31

Bubbled through limewater - turns cloudy.

Question 32

What is the test for Chlorine gas?

Answer 32

Damp blue litmus paper turns red and then bleaches.

Question 33

What is the test for Ammonia gas?

Answer 33

Turns damp red litmus paper blue.

Question 34

What is the chemical reaction for the combustion of Hydrogen?

Answer 34

2H2 + O2 🡪 2H2O.

Question 35

What indicates the presence of water?

Answer 35

White anhydrous copper sulphate turns blue.

Question 36

What are the boiling and freezing points of pure water?

Answer 36

Pure water boils at exactly 100°C and freezes at 0°C.

Question 37

What effect do impurities have on the boiling and freezing points of water?

Answer 37

Impurities will raise the boiling point and lower the freezing point.