Testing for Gases and Water (TOPIC 8)

Question 1

Describe the test for Hydrogen

Answer 1

Hold a lit splint at the end of the test tube - if hydrogen is present the flame will go out with a squeaky pop.

Question 2

Describe the test for Oxygen

Answer 2

Place glowing splint into test tube of gas - if oxygen is present the splint will relight.

This is because the concentration of oxygen inside the tube is higher than the concentration in the air.

Question 3

Describe the test for Carbon Dioxide

Answer 3

Bubble the gas through limewater and if carbon dioxide is present the limewater will turn cloudy as there will be a precipitate of calcium carbonate

Question 4

Describe the test for Ammonia

Answer 4

Place damp red litmus paper into sample of ammonia gas if ammonia is present the litmus paper will turn blue as ammonia is alkaline.

Question 5

Describe the test for Chlorine

Answer 5

Place damp blue litmus paper into the test tube of gas - The litmus paper turns red briefly then white.

It turns white because the litmus paper is bleached by the chlorine gas

Question 6

What is a reversible reaction?

Answer 6

A reversible reaction is a reaction that can occur in the forward direction and the reverse direction

Question 7

Describe the reaction of heat on ammonium chloride in terms of reversible reactions.

Answer 7

When ammonium chloride is heated it reacts to form ammonia and hydrogen chloride.

If it is cooled down the ammonia and hydrogen chloride then react again to form ammonium chloride.

Question 8

Describe the test for the presence of water using anhydrous copper sulfate.

Answer 8

Add the substance to anhydrous copper sulfate which is white. If the substance is water then the white anhydrous copper sulfate will turn blue to form hydrated copper sulfate.

This is a reversible reaction so will turn white if heated.