Chemistry — Periodic Table, Bonding, Acids, Electrolysis, Metallurgy & Organic — Practice

Question 1

Calculate the number of molecules in 44 g of CO₂. (Molecular mass of CO₂ = 44 g/mol, Avogadro's number = 6 × 10²³)

Accepted Answer

Moles of CO₂ = given mass / molar mass = 44 / 44 = 1 mole. Number of molecules = 1 × 6 × 10²³ = 6 × 10²³ molecules. Also: in 1 mole CO₂, there are 1 mole C atoms (= 6 × 10²³ C atoms) and 2 moles O atoms (= 1.2 × 10²⁴ O atoms).

Question 2

Acidified water (dilute H₂SO₄ solution) is electrolysed using platinum electrodes. Identify the products at each electrode. Write the ionic equations. Explain why the volume of gas at the cathode is double that at the anode.

Accepted Answer

CATHODE (−): H⁺ ions are reduced. 2H⁺ + 2e⁻ → H₂ (hydrogen gas produced). ANODE (+): OH⁻ ions are oxidised. 4OH⁻ → 2H₂O + O₂ + 4e⁻ (oxygen gas produced). OVERALL: 2H₂O → 2H₂ + O₂ (electrolysis of water). VOLUME RATIO: From the equation, H₂ : O₂ = 2 : 1. So volume of H₂ at cathode is TWICE the volume of O₂ at anode. (Equal number of moles at same T and P would have equal volume by Avogadro's law; here the mole ratio from the equation is 2:1.)

Question 3

Starting from ethane (C₂H₆), show how you would obtain (a) bromoethane, (b) ethene, (c) ethanol, (d) ethanoic acid (acetic acid). State the type of each reaction.

Accepted Answer

(a) Ethane → Bromoethane: CH₃CH₃ + Br₂ →(UV light)→ CH₃CH₂Br + HBr. Type: SUBSTITUTION (free radical halogenation). (b) Bromoethane → Ethene: CH₃CH₂Br + KOH(alcoholic) → CH₂=CH₂ + KBr + H₂O. Type: ELIMINATION (dehydrohalogenation). Alternatively: Ethane can be cracked/dehydrogenated. (c) Ethene → Ethanol: CH₂=CH₂ + H₂O →(H₃PO₄ catalyst, 300°C, 60 atm)→ CH₃CH₂OH. Type: ADDITION (hydration). (d) Ethanol → Ethanoic Acid: CH₃CH₂OH →(acidified K₂Cr₂O₇ or KMnO₄)→ CH₃COOH. Type: OXIDATION.

Practice — Chemistry — Periodic Table, Bonding, Acids, Electrolysis, Metallurgy & Organic

Sign in to save attempts to your dashboard and track your accuracy over time

Find a verified tutor

Join a live course

Browse coaching centres

About

Categories

Support

Documentation

Get Study Tips & Updates

Download Our App

Download for iOS

Download for Android

Popular Cities