4.6 CHEMICAL TESTS

Question 1

How to carry out a test for hydrogen

Answer 1

• Collect a sample of gas in a test tube
• Attempt to ignite the gas with a lit splint
• You will hear a squeaky pop

Question 2

How to carry out a test for hydrogen

Answer 2

• Collect a sample of gas in a test tube
• Attempt to ignite the gas with a lit splint
• You will hear a squeaky pop

Question 3

What is the chemical reaction when testing hydrogen

Answer 3

Combustion - hydrogen forming water

Question 4

How to test for oxygen

Answer 4

• Collect a sample of gas in a test tube
• Place a glowing splint in the test tube
• The splint will relight

Question 5

What is the chemical reaction taking place when testing for oxygen

Answer 5

Combustion of the wood - Pure O2 is more concentrated that the O2 in normal air (splint combusts faster)

Question 6

How to test for the presnece of water

Answer 6

• Add anhydrous copper (II) sulfate to water
• Will turn from white to blue

Question 7

How to test the purity of water

Answer 7

• Measure the boiling point
• Closer to 100c = more pure

Question 8

How to test for CO2

Answer 8

• Bubble a sample of gas through limewater
• A white precipitate forms (goes cloudy)

Question 9

How to test for CO2

Answer 9

• Bubble a sample of gas through limewater
• A white precipitate forms (goes cloudy)

Question 10

What is the chemical reaction taking place when testing for CO2

Answer 10

• Limewater is saturated calcium hydroxide solution
• Calcium Carbonate is the white precipitate formed with water when reacting

Question 11

How to test for chlorine

Answer 11

• Place damp blue litmus paper in a sample of the gas
• It wil be bleached white

Question 12

What is the chemical reaction occuring, when testing for chlorine

Answer 12

• Chlorine dissolves into the dampness (water) and removes colour from blue litmus
• It is a good bleaching agent

Question 12

What is the chemical reaction occuring, when testing for chlorine

Answer 12

• Chlorine dissolves into the dampness (water) and removes colour from blue litmus
• It is a good bleaching agent

Question 13

How to test for ammonia

Answer 13

• Place damp red litmus paper in sample of gas
• It will turn blue

Question 14

What is the chemical reaction taking place when testing for ammonia

Answer 14

• Ammonia acts as a base accepiting H+ ions from water
• OH- ions remain
• Alkaline so turns litmus blue
• Ammonia + water -> Ammonium + hydroxide

Question 15

Describe how to conduct a flame test

Answer 15

• Dip a piece of nichrome / platinum wire into hydrochloric acid to clean the wire
• Dip the wire into the sample of solid or solution
• Place the tip of the wire into a non-luminous bunsen flame

Question 16

Red flame test result

Answer 16

Li+

Question 17

Yellow flame test result

Answer 17

Na+

Question 18

Lilac flame test result

Answer 18

K+

Question 19

Orange-red flame test result

Answer 19

Ca 2+

Question 20

Blue-green flame test result

Answer 20

Cu 2+

Question 21

Flame test result of Li+

Answer 21

Red

Question 22

Flame test result for Na+

Answer 22

Yellow

Question 23

Flame test result for K+

Answer 23

Lilac

Question 24

Flame test result for Ca 2+

Answer 24

Orange-red

Question 25

Flame test result for Cu 2+

Answer 25

Blue-green

Question 26

How to carry out a NaOH test

Answer 26

* Dissolve sample in water * Add a few drops of NaOH (aq)

Question 27

Cu 2+ result - NaOH test

Answer 27

Blue precipitate forms

Question 28

Fe 3+ result - NaOH test

Answer 28

Brown precipitate forms

Question 29

Fe 2+ result - NaOH test

Answer 29

Green precipitate forms

Question 30

How to carry out ammonium test

Answer 30

* Dissolve sample in water * Add NaOH (aq) and warm it * Test the gas evolved with red litmus paper * Red litmus turns blue

Question 31

What is the chemical reaction taking place when carrying out the ammonium test

Answer 31

Ammonium ions (from sample), and OH - ions (from NaOH) form ammonia

Question 32

How to test for halides

Answer 32

* Dissolve the sample in water * Add nitric acid * Add silver nitrate

Question 33

What ion gives a cream precipitate in silver nitrate test

Answer 33

Br -

Question 34

What ion gives a white precipitate in the silver nitrate test

Answer 34

Cl -

Question 35

What ion gives a yellow precipitate in the silver nitrate test

Answer 35

I -

Question 36

Why must you add nitric acid when carrying out a silver nitrate test

Answer 36

* Ag + ions form precipitates with other anions * The HNO3 reacts with those anions preventing false positives

Question 37

Why must you add nitric acid when carrying out a silver nitrate test

Answer 37

* Ag + ions form precipitates with other anions * The HNO3 reacts with those anions preventing false positives

Question 38

How to test for a carbonate

Answer 38

1. Add hydrochloric acid and look for effervescence 2. If there is effervescene bubble the gas through limewater 3. If ions are present, the gas evolved (CO2) turns limewater cloudy

Question 39

Why must you bubble the gas evolved from a carbonate test through limewater

Answer 39

Acids evolve gases that aren't CO2, so it prevents false positives

Question 39

Why must you bubble the gas evolved from a carbonate test through limewater

Answer 39

Acids evolve gases that aren't CO2, so it prevents false positives

Question 40

How to test for a sulfate

Answer 40

* Add hydrochloric acid and look for effervescence * If there's no effercescence add barium chloride solution * If the ions are present, they will form a white precipitate with the Ba 2+ ions from the BaCl2

Question 41

Why must you still add HCl to a sample testing for a sulfate ion

Answer 41

* Carbonate ions also form a white precipitate with Ba 2+ ions * It prevents a false positive