2h Chemical tests

Question 1

What is the chemical test for hydrogen (H2)?

Answer 1

Hold a lit splint over the mouth of test tube
Positive result - Squeaky pop
H2(g)+o2(g)->H20(l)

Question 2

What is the chemical test for oxygen (o2)?

Answer 2

Put a glowing lit splint into the test tube of gas
Positive result - Splint relights
Combustion of the wood in the splint

Question 3

What is the chemical test for carbon dioxide (CO2)?

Answer 3

Bubble gas through limewater
Positive result - Turns cloudy
Ca(OH)2(aq)+CO2(g)->CaCO3(s)+H2o(l)
Insoluble calcium carbonate is produced forming a white suspension

Question 4

What is the chemical test for Chlorine (Cl2)?

Answer 4

Put damp blue litmus paper in the test tube of gas
Positive result - turns white/bleaches
Cl2 reacts with water to form bleach

Question 5

What is the chemical test for ammonia (NH3)?

Answer 5

Put damp red litmus paper in the test tube of gas
Positive result - turns blue
NH3 is an alkaline gas
NH3(g)+H2O(l)->NH4OH(aq)

Question 6

How to carry out a flame test?

Answer 6

• Heat the bunsen flame and turn it to a roaring flame
• Put a spatula of the solid you are going to test on a watch glass
• Dip the wire into clean hydrochloric acid
• Dip a clean wire loop into a solid sample of the compound being tested
• Put the loop into the edge of the blue flame from a Bunsen burner
• Observe and record the flame colour produced

Question 7

What colour does a lithium ion (Li+) produce?

Answer 7

Red

Question 8

What colour does a sodium ion (Na+) produce?

Answer 8

Yellow

Question 9

What colour does a potassium ion (K+) produce?

Answer 9

Lilac

Question 10

What colour does a magnesium ion (Mg2+) produce?

Answer 10

No colour

Question 11

What colour does a calcium ion (Ca2+) produce?

Answer 11

orange-red

Question 12

What colour does a copper ion (Cu2+) produce?

Answer 12

blue-green

Question 13

How do you carry out a test for cations using sodium hydroxide solution?

Answer 13

Put a 2cm depth of solution to be tested in a test tube

Using a dropper, carefully add several drops of sodium hydroxide solution

Question 14

What colour does calcium (Ca2+) turn when sodium hydroxide is added?

Answer 14

Cloudy (white)

Question 15

What colour does copper (Cu2+) turn when sodium hydroxide is added?

Answer 15

Light Blue

Question 16

What colour does iron(II) (Fe2+) turn when sodium hydroxide is added?

Answer 16

Blue-Green

Question 17

What colour does iron(III) (Fe3+) turn when sodium hydroxide is added?

Answer 17

Red - Brown

Question 18

What colour does potassium (K+) turn when sodium hydroxide is added?

Answer 18

Clear - no reaction

Question 19

What colour does zinc (Zn2+) turn when sodium hydroxide is added?

Answer 19

White precipitate - dissolves in excess sodium hydroxide solution

Question 20

What are the solutions formed when a cation is reacted with sodium hydroxide?

Answer 20

Iron (II) hydroxide
Iron (III) hydroxide
Zinc hydroxide
Calcium hydroxide
Copper hydroxide

Question 21

What are the ionic equations when cations are reacted with sodium hydroxide?

Answer 21

Fe2+(aq) + 2OH-(aq) -> Fe(OH)2(s)
Fe3+(aq) + 3OH-(aq) -> Fe(OH)3(s)
Cu2+(aq) + 2OH-(aq) -> Cu(OH)2(s)
Ca2+(aq) + 2OH-(aq) -> Ca(OH)2(s)
Zn2+(aq) + 2OH-(aq) -> Zn(OH)2(s)

Question 22

What is the test for Ammonium ions (NH4+)?

Answer 22

• Dissolve compound in water
• Add drops of dilute sodium hydroxide (NaOH(aq))
• Warm the mixture over a bunsen burner
• Hold damp red litmus paper over the mouth of the test tube
• If damp red litmus paper turns blue then ammonium compound is present

Question 23

What is the test for a carbonate ion (CO32-)?

Answer 23

• Add hydrochloric acid
• If Carbonate ion is present carbon dioxide will be given off so bubble any gas produced in limewater
• If it turns cloudy then carbonate ion is present

Question 24

What is the test for identifying halides?

Answer 24

Put approximately a 2cm depth of the test solution in a test tube. Add approximately a 1cm depth of dilute nitric acid followed by approximately a 1cm depth of silver nitrate solution

Question 25

What precipitate is formed when nitric acid and silver nitrate solution is added to chloride (Cl-)?

Answer 25

White precipitate

Question 26

What precipitate is formed when nitric acid and silver nitrate solution is added to bromide (Br-)?

Answer 26

Cream precipitate

Question 27

What precipitate is formed when nitric acid and silver nitrate solution is added to iodide (I-)?

Answer 27

Yellow precipitate

Question 28

What is the test for identifying sulfate ions?

Answer 28

Put approximately 2cm depth of the test solution in a test tube. Add approximately a 1cm depth of dilute hydrochloric acid followed by approximately a 1cm depth of barium chloride solution

Question 29

What precipitate is formed when hydrochloric acid and barium chloride is added to a sulfate ion (SO42-)?

Answer 29

White precipitate

Question 30

What is downward delivery?

Answer 30

If a gas is denser than air, it is often more convenient to collect it in a gas jar or test tube by downward delivery.

The gas produced in a chemical reaction is passed through a delivery tube into the gas jar, where it sinks and pushes the air out of the top.

This works well for carbon dioxide and chlorine, which are both denser than air. The equipment must be used in a fume cupboard when chlorine is collected, because chlorine is toxic and has a sharp, choking smell.

Question 31

What is upward delivery?

Answer 31

Preparation and collection if a gas is less dense than air.

The gas produced in a chemical reaction is passed through a delivery tube into the gas jar, where it rises and takes up the space at the top of the jar - pushing the air in the jar down and out at the bottom.

This works well for hydrogen and ammonia, which are both less dense than air. The equipment must be used in a fume cupboard when ammonia is collected, because ammonia is toxic and has a sharp, choking smell.