What is chlorine?
Chlorine is a highly reactive halogen element found mainly in combined form as chlorides.
Why does chlorine not occur freely in nature?
Because it is too reactive and readily combines with other elements.
Give two laboratory methods for preparing chlorine gas.
(i) Oxidation of concentrated HCl with
MnO₂ or KMnO₄.
(ii) Heating concentrated H₂SO₄
with NaCl and MnO₂.
Write the equation for chlorine production using MnO₂ and HCl.
MnO₂ + 4HCl → MnCl₂ + 2H₂O + Cl₂.
State the industrial method for chlorine preparation.
Electrolysis of brine or molten NaCl, MgCl₂, or CaCl₂.
List three physical properties of chlorine gas.
Greenish-yellow gas, choking smell, poisonous, 2.5 times denser than air, moderately soluble in water.
What is the reaction between chlorine and sodium?
2Na + Cl₂ → 2NaCl.
State the reaction between chlorine and hydrogen gas.
Cl₂ + H₂ → 2HCl.
Why is chlorine considered a strong oxidizing agent?
Because it readily gains electrons, oxidizing other substances such as Fe²⁺ to Fe³⁺.
What happens when chlorine reacts with iron(II) chloride solution?
2FeCl₂ + Cl₂ → 2FeCl₃ (oxidation of Fe²⁺ to Fe³⁺).
Write the reaction of chlorine with cold dilute NaOH.
2NaOH + Cl₂ → NaOCl + NaCl + H₂O.
Write the reaction of chlorine with hot concentrated NaOH.
6NaOH + 3Cl₂ → NaClO₃ + NaCl + 3H₂O.
Explain the bleaching action of chlorine.
In water, Cl₂ forms HOCl which decomposes to release oxygen that oxidizes dyes to colorless compounds.
What is the reaction for chlorine with water?
H₂O + Cl₂ → HCl + HOCl.
What compound is formed when chlorine reacts with slaked lime?
Bleaching powder: Ca(OH)₂ + Cl₂ → CaOCl₂·H₂O.
How can chlorine be tested in the laboratory?
It turns damp starch-iodide paper blue and bleaches damp blue litmus paper.
List two industrial uses of chlorine.
Used in making PVC, disinfectants, antiseptics, weed killers, and synthetic rubber.
What is hydrogen chloride gas?
A colorless gas with sharp odor that dissolves in water to form hydrochloric acid.
How is hydrogen chloride gas prepared in the lab?
By heating NaCl with concentrated H₂SO₄: 2NaCl + H₂SO₄ → Na₂SO₄ + 2HCl.
State the industrial method of producing HCl.
By direct combination of H₂ and Cl₂: H₂ + Cl₂ → 2HCl.
List three physical properties of hydrogen chloride gas.
Colorless, sharp smell, forms white fumes in moist air, soluble in water, denser than air.
What happens when HCl reacts with ammonia gas?
HCl + NH₃ → NH₄Cl (white fumes).
Write the reaction between HCl and zinc.
Zn + 2HCl → ZnCl₂ + H₂.
What test confirms hydrogen chloride gas?
Dense white fumes when a glass rod dipped in ammonia is brought near the gas.
Why is dry HCl gas not acidic?
Because it is covalent and does not ionize in nonpolar solvents; it ionizes only in water.
What ions give hydrochloric acid its acidic properties?
H⁺ and Cl⁻ ions formed when HCl dissolves in water.
What are chlorides?
Normal salts formed when hydrogen in HCl is replaced by a metallic ion.
How are chlorides prepared?
By neutralization reactions between hydrochloric acid and bases or metals.
Give examples of soluble chlorides.
NaCl, KCl, CaCl₂, NH₄Cl.
Give examples of insoluble chlorides.
AgCl, PbCl₂, CuCl₂.
State two general properties of chlorides.
They are not decomposed by heat and can be recovered by evaporation or crystallization.
Write the reaction of NaCl with concentrated H₂SO₄.
2NaCl + H₂SO₄ → Na₂SO₄ + 2HCl.
How is chlorine gas produced from chlorides in the lab?
By heating chlorides with concentrated H₂SO₄ and a strong oxidizing agent (e.g., KMnO₄).
Write the reaction producing Cl₂ from ZnCl₂ and KMnO₄.
ZnCl₂ + KMnO₄ + 2H₂SO₄ →
ZnSO₄ +
K₂SO₄
+ 2MnO₂ + 2H₂O + Cl₂.
Describe the test for chlorides.
Add AgNO₃ to acidified solution; white precipitate of AgCl dissolves in excess NH₃.
What is the color of AgCl precipitate?
White, and it dissolves in ammonia solution.
What is the oxidation state of chlorine in NaOCl?
+1 (in sodium hypochlorite).
What is the oxidation state of chlorine in NaClO₃?
+5 (in sodium chlorate).
What gives chlorine its bleaching property?
The release of nascent oxygen from HOCl decomposition.
State one environmental effect of hydrogen chloride gas.
It contributes to acid rain due to its high solubility in water.
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