Answers section

Questions 6.4

Explain the observations in Experiment 1.
Describe the observations in Experiment 2. Explain the observation.
1. Explain the observations in Experiment 3.
2. Explain what would be observed when a blue litmus paper is dropped into the resulting solution.
3. Complete Equation E1 (Experiment 3), and name the gas produced.
1. Write the formula of the solid product in Experiment 4.
2. Write the formula equation for the reaction in Experiment 4.
3. Give a reason for the bright white light produced.
From these experiments, identify any two similarities and two differences between chlorine and sulphur (IV) oxide.
Complete the following table to show direct combination of chlorine gas with other elements.

Element Expected observations when the element is burnt in chlorine gas (Cl₂) Equations

Iron (Fe)

Hydrogen (H₂)

Phosphorus (P)

Sulphur (S)

Draw a set-up you would use to burn hydrogen in chlorine gas. The set-up should include a gas jar.

Answers to Questions 6.4

Chlorine partially dissolves in water to form chlorine water, which contains dilute hydrochloric acid (HCl(aq)) and chloric (I) acid (HOCl(aq). HCl(aq) turns litmus paper red. Then HOCl(aq) bleaches it.
Both glowing and burning wooden splints are extinguished. Chlorine does not support the burning of wood.
(a) Energy from ultraviolet light decomposes the pale green chloric (I) acid (HOCl(aq)) to the colourless hydrochloric acid (HCl) and oxygen, which is released as a gas. The solution therefore turns colourless.
(b) The blue litmus would turn red and remain red, because there is no more HOCl(aq) to bleach it.
(c) 2HOCl(aq) 2HCl(aq) + O₂(g)

(a) MgCl₂
(b) Mg(s) + Cl₂(g) → MgCl₂(s)
(c) The reaction produces a lot heat and light energy.

Similarities: Like sulphur (IV) oxide, chlorine has a pungent irritating smell, and causes bleaching. Differences: Chlorine bleaches by oxidation, whereas sulphur (IV) oxide bleaches by reduction. Chlorine is pale yellow (yellow-green); but sulphur (IV) oxide is colourless.

Element	Expected observations when the element is burnt in chlorine gas (Cl₂)	Equations
Iron (Fe)	A bright red glow; red-brown fumes which settle as a red-brown solid on cooler parts of the vessel.	2Fe(s) + 3Cl₂(g) → 2FeCl₃(g)
Hydrogen (H₂)	Hydrogen continues to burn with a blue flame in chlorine gas. The product is white substance (fumes) with a chocking smell and which turns colourless as it disperses.	H₂(g) + Cl₂(g) → 2HCl(g) Caution: Both hydrogen and chlorine should be dry and uncontaminated with air to avoid explosive burning of hydrogen.
Phosphorus (P)	Phosphorus burns in chlorine gas with a bright white flame to form thick white fumes that settle as a white solid.	P₄(s) + 10Cl₂(g) → 4PCl₅(s). P₄(s) + 6Cl₂(g) → 4PCl₃(s)
Sulphur (S)	Sulphur burns in chlorine gas with a blue flame to form a colourless gas with a chocking smell.	S(s) + Cl₂(g) → SCl₂(g)