10th Class Chemistry — MCQs & Practice Questions

Particles are closely packed in a regular, fixed arrangement and can only vibrate about fixed positions.

Gas particles move rapidly in all directions and collide with the walls; the force of these collisions per unit area is the pressure.

Heating gives particles more kinetic energy so they vibrate more; at the melting point the forces holding the lattice break and particles move past each other (liquid); at the boiling point particles gain enough energy to escape completely (gas).

1. Diffusion is the movement of particles from a region of higher concentration to lower concentration[1]
2. ...until they are evenly spread / down a concentration gradient[1]
3. Bromine molecules are heavier / have greater mass than hydrogen molecules[1]
4. At the same temperature heavier particles move more slowly, so diffuse more slowly[1]
5. Raising temperature increases the rate of diffusion[1]
6. Because particles gain kinetic energy and move faster[1]

Diffusion = spreading down a concentration gradient; lighter particles diffuse faster; higher temperature → faster diffusion.

Before melting the temperature rises as particles gain kinetic energy. During melting it stays constant (a plateau) because the energy overcomes the forces holding the lattice. After melting it rises again as the liquid warms.

1. Particles move rapidly and randomly, colliding with the walls[1]
2. the force of these collisions per unit area is the pressure[1]
3. Heating gives particles more kinetic energy so they move faster[1]
4. collisions are harder and more frequent, so pressure rises[1]
5. Halving the volume means the same particles are in a smaller space[1]
6. so collisions with the walls are twice as frequent and the pressure doubles[1]

Pressure = wall collisions per area; heating raises it (faster, more frequent collisions); halving the volume doubles it (more frequent collisions).

Mr of CH₄ = 12 + 4 = 16. Moles = mass ÷ Mr = 8.0 ÷ 16 = 0.50 mol.

The sum of the relative atomic masses of all the atoms shown in the molecular formula of a substance.

4 Al + 3 O₂ → 2 Al₂O₃.

1. Mr(CaCO₃) = 40 + 12 + 48 = 100[1]
2. Moles CaCO₃ = 25 ÷ 100 = 0.25 mol[1]
3. Moles CaO = 0.25 (1:1 ratio); Mr(CaO) = 56[1]
4. Mass CaO = 0.25 × 56 = 14 g[1]
5. Moles CO₂ = 0.25 (1:1 ratio)[1]
6. Volume = moles × 24 = 0.25 × 24[1]
7. Volume CO₂ = 6.0 dm³[1]

Mr = 100; 14 g CaO; 6.0 dm³ CO₂.

V = 500 ÷ 1000 = 0.50 dm³. c = n ÷ V = 0.20 ÷ 0.50 = 0.40 mol/dm³.

1. Mr(Fe₂O₃) = 112 + 48 = 160[1]
2. Moles Fe₂O₃ = 320 ÷ 160 = 2 (tonne-moles)[1]
3. Moles Fe = 2 × 2 = 4; Ar(Fe) = 56[1]
4. Mass Fe = 4 × 56 = 224 tonnes[1]
5. Desired product mass in equation = 2 × 56 = 112; total product mass = 112 + 3 × 44 = 244[1]
6. Atom economy = (112 ÷ 244) × 100[1]
7. = 45.9% (≈ 46%)[1]

Mr = 160; 224 tonnes of iron; atom economy ≈ 46%.

Oxidation is loss of electrons; reduction is gain of electrons (OIL RIG).

The breakdown (decomposition) of an ionic compound, when molten or in aqueous solution, by the passage of an electric current.

Cathode (−): Pb²⁺ + 2e⁻ → Pb (lead metal). Anode (+): 2Br⁻ → Br₂ + 2e⁻ (bromine gas).

1. Melting frees the ions[1]
2. so they can move to the electrodes and carry the current[1]
3. Al³⁺ + 3e⁻ → Al[1]
4. balanced with electrons[1]
5. Oxygen is produced at the anode[1]
6. The hot oxygen reacts with the carbon anodes forming carbon dioxide[1]
7. so the anodes burn away and must be replaced[1]

Molten = mobile ions to carry current; cathode Al³⁺ + 3e⁻ → Al; anode makes O₂, which burns the carbon anodes to CO₂ so they wear away.

Oxygen is −2, so 4 × (−2) = −8. The whole ion has a charge of −1, so Mn + (−8) = −1, giving Mn = +7.

1. The anode (positive electrode) is the impure copper[1]
2. Cu → Cu²⁺ + 2e⁻ (copper dissolves)[1]
3. Pure copper deposits on the cathode[1]
4. Cu²⁺ + 2e⁻ → Cu[1]
5. Impurities do not dissolve / are not deposited[1]
6. they collect below the anode as anode sludge[1]

Anode = impure copper (Cu → Cu²⁺ + 2e⁻); cathode gains pure copper (Cu²⁺ + 2e⁻ → Cu); impurities drop as anode sludge.

Particles must collide, and they must collide with enough energy (at least the activation energy) and correct orientation.

Higher concentration means more particles per unit volume, so collisions are more frequent, increasing the rate.

A catalyst provides an alternative reaction pathway with a lower activation energy, so a greater proportion of collisions are successful, increasing the rate. It is not used up.

1. At higher temperature particles have more kinetic energy and move faster[1]
2. Collisions are more frequent[1]
3. and a greater proportion have energy ≥ activation energy, so more are successful[1]
4. Powder has a larger surface area (area to volume)[1]
5. so more frequent collisions with acid particles / more sites for reaction[1]
6. The rate is the gradient (slope) of the graph[1]

Higher temperature: faster, more energetic collisions; powder: greater surface area → more frequent collisions; rate = gradient of the volume–time graph.

Collect the gas in a gas syringe and record the volume at fixed times, or stand the flask on a balance and record the loss in mass as the gas escapes.

1. Particles gain kinetic energy and move faster, so collisions are more frequent[1]
2. a greater proportion of collisions have energy above the activation energy[1]
3. so a much larger fraction are successful — the rate rises sharply[1]
4. A catalyst provides an alternative pathway with a lower activation energy[1]
5. so a greater fraction of the existing molecules have enough energy to react[1]
6. more successful collisions per second; the catalyst is not used up[1]

Higher temperature: faster, more energetic collisions, more exceed Ea. Catalyst: lower Ea, so more molecules already exceed it; recovered unchanged.

Acids produce hydrogen ions, H⁺, in aqueous solution; their pH is below 7.

A strong acid is fully ionised in water; a weak acid is only partly ionised. It is about degree of ionisation, not concentration.

Hydrochloric acid + sodium hydroxide → sodium chloride + water. HCl + NaOH → NaCl + H₂O.

1. CuO + H₂SO₄ → CuSO₄ + H₂O (correct formulae)[1]
2. Equation balanced[1]
3. Warm the acid and add excess copper(II) oxide, then filter off the unreacted solid[1]
4. Heat the filtrate to evaporate some water / to the point of crystallisation[1]
5. Leave to cool so crystals form[1]
6. Filter and dry the crystals (e.g. between filter paper)[1]
7. Excess ensures all the acid reacts, and the excess solid can simply be filtered off[1]

CuO + H₂SO₄ → CuSO₄ + H₂O; react with excess base, filter, evaporate to crystallisation, cool, filter, dry; excess guarantees all acid used and is easily removed.

pH = −log₁₀(1 × 10⁻³) = 3. pH 3 is below 7, so the solution is acidic.

1. CuO + H₂SO₄ → CuSO₄ + H₂O (correct formulae)[1]
2. balanced[1]
3. Warm the acid and add copper(II) oxide in excess until no more reacts[1]
4. Filter to remove the excess copper(II) oxide[1]
5. Heat the filtrate to evaporate water to the point of crystallisation, then leave to cool[1]
6. Filter off the crystals and dry them (e.g. between filter paper)[1]

CuO + H₂SO₄ → CuSO₄ + H₂O; react with excess base, filter, evaporate to crystallisation, cool, filter, dry.

Reactivity decreases down the group because the outer shell is further from the nucleus and more shielded, so it is harder to attract an electron.

Damp red litmus paper turns blue in ammonia gas (ammonia is alkaline).

Chlorine is more reactive (a stronger oxidising agent) than bromine, so it removes electrons from bromide ions: Cl₂ + 2Br⁻ → 2Cl⁻ + Br₂.

1. Sulfur dioxide and nitrogen oxides are released when fossil fuels burn[1]
2. They dissolve in rainwater[1]
3. forming acidic solutions (sulfurous/sulfuric and nitric acids)[1]
4. SO₂ + H₂O → H₂SO₃[1]
5. Damages plants/forests, or acidifies lakes killing fish[1]
6. or corrodes buildings/limestone and metals (any valid effect)[1]

SO₂/NOₓ from burning fuels dissolve in rain forming acids; SO₂ + H₂O → H₂SO₃; acid rain damages forests, lakes, buildings.

With potassium bromide the solution turns orange as bromine is displaced; with potassium iodide it turns brown as iodine is displaced. Chlorine is more reactive than both. Equation: Cl₂ + 2KBr → 2KCl + Br₂.

1. Halogens react by gaining one electron[1]
2. down the group the outer shell is further from the nucleus and more shielded[1]
3. so an electron is attracted/gained less easily — reactivity falls[1]
4. The inert pair effect is the reluctance of the outer s-electron pair to bond in heavier p-block elements[1]
5. so they favour an oxidation state two lower than the group maximum[1]
6. lead is more stable as Pb²⁺ than Pb⁴⁺[1]

Halogen reactivity falls down the group (electron gained less easily); the inert pair effect makes heavier elements like lead favour the lower (+2) state.

About 78% nitrogen and about 21% oxygen (the remaining ~1% is mostly argon with a little carbon dioxide).

Add anhydrous copper(II) sulfate — it turns from white to blue in the presence of water (or blue cobalt chloride paper turns pink).

Carbon dioxide is a greenhouse gas; it absorbs and re-emits heat (infrared radiation) that would otherwise escape, so the extra CO₂ traps more heat and raises average global temperatures.

1. Water (moisture)[1]
2. Oxygen (air)[1]
3. Galvanising coats the iron with a layer of zinc[1]
4. The zinc is more reactive than iron, so it corrodes/loses electrons in preference (sacrificial protection)[1]
5. so the iron is protected even where the coating is scratched[1]
6. Painting / oiling / greasing / coating with plastic (any one)[1]

Water + oxygen needed; galvanising = zinc coating that sacrificially protects (zinc more reactive) even if scratched; also painting/oiling.

Sulfur impurities in the coal burn to sulfur dioxide, which dissolves in rainwater to form an acidic solution (sulfurous/sulfuric acid). This acid rain damages plants and forests, acidifies lakes killing fish, or corrodes limestone buildings and metals.

1. Carbon monoxide forms by incomplete combustion[1]
2. when there is not enough oxygen to make CO₂[1]
3. it is toxic because it prevents the blood from carrying oxygen[1]
4. The converter provides a catalyst surface where pollutants react[1]
5. carbon monoxide is oxidised to carbon dioxide[1]
6. 2CO + O₂ → 2CO₂ (and NOₓ is reduced to N₂)[1]

CO from incomplete combustion, toxic (stops blood carrying O₂); catalytic converter oxidises CO to CO₂ (2CO + O₂ → 2CO₂) and reduces NOₓ to N₂.

A family of organic compounds with the same general formula and similar chemical properties, where each member differs from the next by CH₂.

Add bromine water: an alkene decolourises it (orange to colourless); an alkane does not (stays orange).

Many ethene monomers (with C=C double bonds) join together, with no other product, to form a long-chain polymer. Repeat unit: –(CH₂–CH₂)–.

1. C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂[1]
2. correct formulae / balanced[1]
3. Steam / water, ~300 °C, ~60 atm, phosphoric acid catalyst[1]
4. C₂H₄ + H₂O → C₂H₅OH[1]
5. balanced equation[1]
6. It is a continuous process / faster / gives purer ethanol (any one)[1]

Fermentation: C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂; hydration: C₂H₄ + H₂O → C₂H₅OH (steam, ~300 °C, ~60 atm, H₃PO₄); hydration is continuous/faster/purer.

Add bromine water: ethene (an alkene) decolourises it from orange to colourless; ethane (an alkane) leaves it orange (no reaction).

1. Cracking breaks long-chain hydrocarbons into shorter ones[1]
2. using heat and a catalyst[1]
3. to make more useful small molecules (fuels) and alkenes for plastics[1]
4. Many ethene monomers (with C=C double bonds) join together[1]
5. the double bonds open and link into a long chain, with no other product[1]
6. The product is poly(ethene)[1]

Cracking breaks long hydrocarbons (heat + catalyst) into useful short molecules and alkenes; addition polymerisation joins many ethene monomers into poly(ethene).

Free-radical substitution. Initiation: Cl₂ → 2Cl• (UV). Propagation: Cl• + CH₄ → •CH₃ + HCl, then •CH₃ + Cl₂ → CH₃Cl + Cl•.

1. The mechanism is electrophilic addition[1]
2. the electron-rich C=C double bond attracts the electrophile (the δ+ H of HBr)[1]
3. The H can add to either carbon, giving either a secondary or a primary carbocation[1]
4. the secondary carbocation is more stable than the primary[1]
5. so the H adds to the terminal (CH₂) carbon (Markovnikov's rule)[1]
6. giving mainly 2-bromobutane[1]

Electrophilic addition; the C=C attracts the electrophile; via the more stable secondary carbocation the major product is 2-bromobutane.

C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂, using yeast at about 30 °C in the absence of air. An advantage is that it uses a renewable resource (sugar/plant crops) rather than crude oil.

1. Oxidise the ethanol with acidified potassium dichromate (warm/reflux)[1]
2. (or ferment ethanol in air) to give ethanoic acid[1]
3. The magnesium fizzes / dissolves, giving off hydrogen gas[1]
4. Mg + 2CH₃COOH → (CH₃COO)₂Mg + H₂[1]
5. Ethyl ethanoate is formed, plus water[1]
6. using a concentrated sulfuric acid catalyst[1]

Oxidise ethanol → ethanoic acid; with magnesium it fizzes giving H₂ (Mg + 2CH₃COOH → (CH₃COO)₂Mg + H₂); with ethanol it makes ethyl ethanoate + water (conc. H₂SO₄ catalyst).

A family of organic compounds with the same general formula and similar chemical properties, where each member differs from the next by CH₂.

Add bromine water: an alkene decolourises it (orange to colourless); an alkane does not (stays orange).

Many ethene monomers (with C=C double bonds) join together, with no other product, to form a long-chain polymer. Repeat unit: –(CH₂–CH₂)–.

1. C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂[1]
2. correct formulae / balanced[1]
3. Steam / water, ~300 °C, ~60 atm, phosphoric acid catalyst[1]
4. C₂H₄ + H₂O → C₂H₅OH[1]
5. balanced equation[1]
6. It is a continuous process / faster / gives purer ethanol (any one)[1]

Fermentation: C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂; hydration: C₂H₄ + H₂O → C₂H₅OH (steam, ~300 °C, ~60 atm, H₃PO₄); hydration is continuous/faster/purer.

Add bromine water: ethene (an alkene) decolourises it from orange to colourless; ethane (an alkane) leaves it orange (no reaction).

1. Cracking breaks long-chain hydrocarbons into shorter ones[1]
2. using heat and a catalyst[1]
3. to make more useful small molecules (fuels) and alkenes for plastics[1]
4. Many ethene monomers (with C=C double bonds) join together[1]
5. the double bonds open and link into a long chain, with no other product[1]
6. The product is poly(ethene)[1]

Cracking breaks long hydrocarbons (heat + catalyst) into useful short molecules and alkenes; addition polymerisation joins many ethene monomers into poly(ethene).

Free-radical substitution. Initiation: Cl₂ → 2Cl• (UV). Propagation: Cl• + CH₄ → •CH₃ + HCl, then •CH₃ + Cl₂ → CH₃Cl + Cl•.

1. The mechanism is electrophilic addition[1]
2. the electron-rich C=C double bond attracts the electrophile (the δ+ H of HBr)[1]
3. The H can add to either carbon, giving either a secondary or a primary carbocation[1]
4. the secondary carbocation is more stable than the primary[1]
5. so the H adds to the terminal (CH₂) carbon (Markovnikov's rule)[1]
6. giving mainly 2-bromobutane[1]

Electrophilic addition; the C=C attracts the electrophile; via the more stable secondary carbocation the major product is 2-bromobutane.

C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂, using yeast at about 30 °C in the absence of air. An advantage is that it uses a renewable resource (sugar/plant crops) rather than crude oil.

1. Oxidise the ethanol with acidified potassium dichromate (warm/reflux)[1]
2. (or ferment ethanol in air) to give ethanoic acid[1]
3. The magnesium fizzes / dissolves, giving off hydrogen gas[1]
4. Mg + 2CH₃COOH → (CH₃COO)₂Mg + H₂[1]
5. Ethyl ethanoate is formed, plus water[1]
6. using a concentrated sulfuric acid catalyst[1]

Oxidise ethanol → ethanoic acid; with magnesium it fizzes giving H₂ (Mg + 2CH₃COOH → (CH₃COO)₂Mg + H₂); with ethanol it makes ethyl ethanoate + water (conc. H₂SO₄ catalyst).

Secondary — the carbon bearing the –OH group is attached to two other carbon atoms.

First an aldehyde, then on further oxidation a carboxylic acid; the dichromate turns from orange to green.

When phenol loses H⁺, the negative charge is delocalised into the benzene ring, stabilising the ion, so H⁺ is released. Ethanol's anion is not stabilised in this way, so it does not release H⁺.

1. Propan-1-ol (primary) → propanal then propanoic acid[1]
2. Propan-2-ol (secondary) → propanone (a ketone)[1]
3. 2-methylpropan-2-ol (tertiary) → no reaction[1]
4. Those that react turn the dichromate from orange to green[1]
5. The tertiary alcohol has no hydrogen on the carbon bearing the –OH[1]
6. so there is nothing for the oxidising agent to remove[1]

1° → aldehyde/acid, 2° → ketone, 3° → no reaction (orange→green for the first two); tertiary resists because there is no H on the OH carbon.

Hydration is a fast, continuous process that gives pure ethanol directly, whereas fermentation is slow, works in batches and produces a dilute impure mixture that must be distilled.

1. When phenol loses H⁺, the negative charge is delocalised into the benzene ring[1]
2. this stabilises the phenoxide ion, so H⁺ is released — weakly acidic[1]
3. ethanol's anion is not stabilised in this way, so it does not release H⁺[1]
4. Add sodium carbonate solution to each[1]
5. the carboxylic acid fizzes, releasing CO₂[1]
6. phenol shows no reaction (too weak an acid)[1]

Phenol is acidic because the ring stabilises the phenoxide ion; ethanol's is not. Sodium carbonate fizzes with a carboxylic acid but not with phenol.

The carboxyl group, –COOH; carboxylic acids are weak acids (only partly ionised in water).

Sodium ethanoate, water and carbon dioxide are formed; effervescence (fizzing) is seen.

When a carboxylic acid loses H⁺, the negative charge on the carboxylate ion is delocalised over both oxygen atoms, stabilising it; an alcohol's anion is not stabilised in this way.

1. The reaction is esterification (condensation)[1]
2. The product is ethyl ethanoate (an ester)[1]
3. CH₃COOH + C₂H₅OH ⇌ CH₃COOC₂H₅ + H₂O[1]
4. balanced with water as the other product[1]
5. The sulfuric acid is a catalyst (and dehydrating agent)[1]
6. Esters are used as flavourings / perfumes / solvents (any one)[1]

Esterification → ethyl ethanoate; CH₃COOH + C₂H₅OH ⇌ CH₃COOC₂H₅ + H₂O; H₂SO₄ is the catalyst; esters used as flavourings/perfumes/solvents.

Propyl ethanoate, formed with a concentrated sulfuric acid catalyst (which also removes water).

1. CH₃COOH + C₂H₅OH ⇌ CH₃COOC₂H₅ + H₂O[1]
2. conditions: warm with a concentrated sulfuric acid catalyst[1]
3. the reaction is reversible[1]
4. (i) with dilute acid: ethanoic acid + ethanol[1]
5. (ii) with sodium hydroxide: sodium ethanoate[1]
6. plus ethanol[1]

CH₃COOH + C₂H₅OH ⇌ CH₃COOC₂H₅ + H₂O (conc. H₂SO₄); acid hydrolysis → acid + alcohol; alkaline hydrolysis → sodium ethanoate + ethanol.

Carbohydrates (from simple sugars), proteins (from amino acids) and fats/lipids (from fatty acids and glycerol).

Add biuret reagent (sodium hydroxide then copper(II) sulfate solution); a positive result is a colour change from blue to purple/violet.

Starch is broken down (hydrolysed) into simple sugars such as glucose. Enzymes are biological catalysts that speed up this reaction at body temperature, which would otherwise be far too slow.

1. It speeds up a reaction[1]
2. without being used up / by lowering the activation energy[1]
3. As temperature rises up to the optimum, activity increases[1]
4. because particles collide more frequently and with more energy[1]
5. Above the optimum, activity falls sharply[1]
6. because the enzyme is denatured — its shape (active site) changes so substrate no longer fits[1]

Catalyst = speeds a reaction without being used up; activity rises to an optimum then falls as the enzyme denatures (active site changes shape).

Condensation joins two monomers together and releases a small molecule (usually water), building a polymer. Hydrolysis is the reverse: it adds water to split a polymer back into its monomers, as in digestion.

1. Starch: add iodine solution[1]
2. a blue-black colour is a positive result[1]
3. Protein: add biuret solution[1]
4. a purple/violet colour is a positive result[1]
5. A cloudy emulsion shows a lipid (fat) is present[1]
6. dissolve the sample in ethanol then add water — a cloudy white emulsion forms[1]

Starch → iodine blue-black; protein → biuret purple; lipid → cloudy emulsion (ethanol then water).

A zwitterion is an amino acid that has transferred a proton internally from its –COOH to its –NH₂, giving –NH₃⁺ and –COO⁻ ends and no overall charge. It can accept H⁺ (onto –COO⁻) in acid and donate H⁺ (from –NH₃⁺) in alkali, so it resists pH change — acting as a buffer.