Identification of Common Gases

1. What gas causes a pop sound when tested with a lighted splint?

Answer: hydrogen


2. What gas causes a glowing splint to relight?

Answer: oxygen


3. What is the aqueous solution used to test for carbon dioxide?

Answer: limewater


4. What happens to damp blue litmus paper when it is put into chlorine gas?

Answer: Turns red then white (is bleached).


5. Calcium carbonate can undergo thermal decomposition to make calcium oxide and a gas.

a) State if this reaction is exothermic or endothermic.

Answer: endothermic


b) State the formula of the gas produced.

Answer: CO2


c) The gas can be tested with limewater. Describe the observation you would expect.

Answer: Limewater goes from colourless to cloudy.


d) Add the state symbols to the balanced symbol equation: CO2 + Ca(OH)2  →  CaCO3 + H2O

Answer: CO2(g) + Ca(OH)2(aq)  →  CaCO3(s)+ H2O(l)


6. Hydrogen peroxide (H2O2 ) can decompose to make water and oxygen gas.

a) Write a balanced symbol equation for this reaction.

Answer: 2H2O2  →  2H2O + O2


b) Outline the chemical test to show that oxygen has been made.

Answer: glowing splint, re-lights


c) Oxygen forms a diatomic molecule. Draw the dot and cross diagram of oxygen.

Answer: