Study Guides/Chemistry/Bleaching Powder Formula — Chemical Name & Composition
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Bleaching Powder Formula, Chemical Name and Composition

The chemical formula of bleaching powder is CaOCl₂, also written as Ca(OCl)Cl. Its chemical name is calcium hypochlorite-calcium chloride or calcium chlorohypochlorite. Bleaching powder is prepared by passing chlorine gas over dry slaked lime [Ca(OH)₂]: Ca(OH)₂ + Cl₂ → CaOCl₂ + H₂O. It is a pale yellow powder with a strong smell of chlorine.

Question (Click to Flip)

What is the chemical formula of bleaching powder?

Answer

The chemical formula of bleaching powder is CaOCl₂, also written as Ca(OCl)Cl. Its chemical name is calcium hypochlorite-calcium chloride or calcium chlorohypochlorite.

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Key Facts

Bleaching powder formula: CaOCl₂ or Ca(OCl)Cl.

Chemical name: calcium hypochlorite-calcium chloride (calcium chlorohypochlorite).

Prepared by: Ca(OH)₂ + Cl₂ → CaOCl₂ + H₂O (at below 40°C).

It is a pale yellowish-white powder with a strong chlorine smell.

Active bleaching agent is hypochlorous acid (HOCl) released in water.

Reacts with CO₂ to release Cl₂: CaOCl₂ + CO₂ → CaCO₃ + Cl₂.

Loses bleaching power on prolonged exposure to air.

Bleaching powder is a mixture — not pure calcium hypochlorite.

Formula and Chemical Name

Chemical formula: CaOCl₂ or Ca(OCl)Cl

Alternative representations: • CaOCl₂ (simplified formula) • Ca(OCl)Cl (structural formula showing both OCl and Cl groups) • Ca(ClO)Cl

Chemical names used: • Calcium hypochlorite-calcium chloride (mixture name) • Calcium chlorohypochlorite • Chlorinated lime • Bleaching powder

Note: Bleaching powder is not pure calcium hypochlorite Ca(OCl)₂. It is a mixture of calcium hypochlorite Ca(OCl)₂ and calcium chloride CaCl₂, along with Ca(OH)₂. The simplified formula CaOCl₂ represents this mixed compound.

Preparation of Bleaching Powder

Bleaching powder is prepared by passing chlorine gas over dry slaked lime at 40°C:

Ca(OH)₂ + Cl₂ → CaOCl₂ + H₂O

Word equation: Slaked lime + Chlorine → Bleaching powder + Water

Conditions: • Temperature should not exceed 40°C (above 40°C, Ca(OCl)₂ decomposes) • Ca(OH)₂ must be dry • Chlorine gas is passed in controlled amounts

Industrially: Chlorine gas from electrolysis of brine is passed over lime in rotating cylinders at 35–40°C.

Properties of Bleaching Powder

Physical properties: • Pale yellowish-white powder • Strong, characteristic smell of chlorine • Partially soluble in water • Gives a white suspension when mixed with water

Chemical properties:

  1. Reacts with CO₂ to release Cl₂: CaOCl₂ + CO₂ → CaCO₃ + Cl₂

  2. Reacts with dilute acids to release Cl₂: CaOCl₂ + H₂SO₄ → CaSO₄ + Cl₂ + H₂O

  3. Active ingredient is hypochlorous acid (HOCl) — formed when bleaching powder dissolves in water: CaOCl₂ + H₂O → Ca(OH)₂ + 2HOCl

  4. Slowly decomposes in air — loses bleaching power over time.

Questions and Answers

What is the chemical formula of bleaching powder?+

The chemical formula of bleaching powder is CaOCl₂, also written as Ca(OCl)Cl. Its chemical name is calcium hypochlorite-calcium chloride or calcium chlorohypochlorite.

How is bleaching powder prepared?+

Bleaching powder is prepared by passing chlorine gas over dry slaked lime at below 40°C: Ca(OH)₂ + Cl₂ → CaOCl₂ + H₂O. The temperature must be kept below 40°C to prevent decomposition of the product.

What is the active bleaching component in bleaching powder?+

The active bleaching component is hypochlorous acid (HOCl), which is released when bleaching powder dissolves in water: CaOCl₂ + H₂O → Ca(OH)₂ + 2HOCl. HOCl releases nascent oxygen which oxidises coloured substances, causing bleaching.

Is bleaching powder the same as calcium hypochlorite?+

No. Bleaching powder (CaOCl₂) is not the same as pure calcium hypochlorite Ca(OCl)₂. Bleaching powder is a mixture compound containing both hypochlorite and chloride groups bound to calcium.

Why does bleaching powder lose its bleaching power on exposure to air?+

Bleaching powder reacts with CO₂ in air: CaOCl₂ + CO₂ → CaCO₃ + Cl₂. The chlorine is released and escapes, reducing the active bleaching agent content. Prolonged exposure to air and moisture causes complete loss of bleaching power.

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