5.0 Sulphur and its Compounds

5.4.1 Chemical properties of hydrogen sulphide

Reaction with water

H₂S(g) + H₂O(l) → H₂S(aq)

Questions 5.4.1(a)

1. From the demonstration, state with reason whether hydrogen sulphide is acidic or basic.
2. What is the evidence that hydrogen sulphide reacts with water?

Answers to Questions 5.4.1(a)

Combustion in air

Observe the video demonstration of combustion of hydrogen sulphide in air, and the accompanying pictures in Figure 5.4.1(b).

Condition	Observations when hydrogen sulphide is burning in oxygen (or air)
Limited supply of oxygen	https://www.sciencedirect.com/topics/earth-and-planetary-sciences/hydrogen-sulphide
Excess oxygen	Insert diagram

Figure 5.4.1(b): Combustion of hydrogen sulphide in air

Questions 5.4.1(b)

Complete the following table to describe, in words and chemical equations, the burning of hydrogen sulphide in air.

Condition	Observations when hydrogen sulphide is burning in oxygen (or air)	Equation for the reaction
Limited supply of oxygen
Excess oxygen

Answers to Questions 5.4.1(b)

Reducing property of hydrogen sulphide

Observe the video demonstration of reducing property of hydrogen sulphide, and the accompanying pictures in Figure 5.4.1(c).

(courtesy Youtube-Reducing Agents: Preparation and Tests for SO2 and H2S. by FranklyChemistry)

Questions 5.4.1(c)

1. Complete the following table to describe, in words and chemical equations, the reducing property of hydrogen sulphide.

   Substance	Observations when hydrogen sulphide is reacted with the substance	Equation for the reaction
   SO2(g)
   NO2(g)
   Br2(aq)
   FeCl3(aq)
   KMnO4(aq)
   K2Cr2O7(aq)
   H2O2(aq)
   HNO3(aq)
   H2SO4(aq)

2. State the common observation in all these demonstrations, neglecting the acids.

Answers to Questions 5.4.1(c)

Precipitation of metallic ions

Observe the video demonstration of precipitation of metallic ions by hydrogen sulphide, and the accompanying pictures in Figure 5.4.1(d).

(courtesy Youtube-Sulphur and its Compounds:-Properties of Hydrogen Sulphide-11 by OAKS - Your Personalised Learning Companion)

Metallic ions	Observations when hydrogen sulphide is bubbled through a solution of the metallic ions
Cu2+
Pb2+
Fe2+
Zn2+

Questions 5.4.1(d)

1. Complete the following table to describe, in words and chemical equations, the precipitation of metallic ions by hydrogen sulphide. Hint: The gas first dissolves in water to produce sulphide ions (S^2-) and hydrogen ions, H⁺ (which remains in solution).
   

   Metallic ions	Observations when hydrogen sulphide is bubbled through a solution of the ions	Equation for the reaction
   Cu2+(aq)
   Pb2+(aq)
   Fe2+(aq)
   Zn2+(aq)



2. Metal sulphides are salts. (a) Write a general conclusion about the solubility of metal sulphides. (b) Suggest three possible exceptions to your conclusion in (a).
3. Explain why the reactions with metallic ions are considered as precipitation and not reduction reactions (Hint: Are there ions in the solid metal sulphides?)
4. 1. Although hydrogen sulphide precipitates other metallic ions, only precipitation of lead (II) ions is used as a confirmatory test for the gas. Explain.
   2. Identify one other compound of lead that may be used as an alternative to lead acetate, in testing for hydrogen sulphide. Explain your choice.
5. Name two of the substances that could be responsible for the blackness of waste and sewage water.

Answers to Questions 5.4.1(d)