Use a copy of the Periodic Table where you need one.
A student was given 4.0 g of magnesium carbonate powder and 100 cm3 of 0.1 mol/dm3 hydrochloric acid. He wants to determine the rate of reaction by measuring the change in mass of the reaction mixture. Which apparatus is not likely to be used in this experiment?
Source: 2024 CHIJ Prelim P1 Q2
Which statement about the Haber process for the manufacture of ammonia is correct?
Source: 2025 TKGS Prelim P1 Q18
Excess magnesium powder is added to 25 cm3 of 0.10 mol/dm3 solutions of three different acids: experiment 1, methanoic acid; experiment 2, hydrochloric acid; experiment 3, sulfuric acid. Which statement is correct?
Source: 2023 SJI Prelim P1 Q19
A series of experiments was carried out to investigate the effect of concentration on the rate of reaction: BrO3−(aq) + 5Br−(aq) + 6H+(aq) → 3Br2(aq) + 3H2O(l). The table shows the initial rates when the concentrations of the reactants were changed.
| experiment | concentration of BrO3− / mol/dm3 | concentration of Br− / mol/dm3 | concentration of H+ / mol/dm3 | initial rate / mol/dm3/s |
|---|---|---|---|---|
| 1 | 1.00 | 1.00 | 1.00 | 0.008 |
| 2 | 2.00 | 1.00 | 1.00 | 0.016 |
| 3 | 1.00 | 2.00 | 1.00 | 0.032 |
| 4 | 2.00 | 1.00 | 2.00 | 0.032 |
Source: 2024 Compassvale Prelim P2 A6(a) and (b)
A student carried out two experiments with calcium carbonate and sulfuric acid: CaCO3 + H2SO4 → CaSO4 + H2O + CO2. The volume of carbon dioxide was measured every minute. In experiment 1, 1.20 dm3 of gas was collected in total.
| experiment | moles of calcium carbonate / mol | moles of sulfuric acid / mol | concentration of sulfuric acid / mol/dm3 |
|---|---|---|---|
| 1 | 0.06 | 0.05 | 2.00 |
| 2 | 0.06 | 0.02 | 4.00 |
Source: 2026 ZHSS Prelim P2 A3 (adapted)
Dtest-tube[1]
The mixture is weighed in a conical flask on a balance, with readings taken against a stopwatch. No test-tube is needed.
BAt higher pressure, the yield increases and the rate of production of ammonia is faster.[1]
A higher pressure increases both the yield and the rate. A higher temperature lowers the yield, and a catalyst does not change the yield.
BExperiments 1 and 2 produced the same volume of gas.[1]
Methanoic acid and hydrochloric acid each give one hydrogen ion per molecule, and the same amount of each acid is used, so they give the same volume of hydrogen. Methanoic acid is weak, so it reacts more slowly.
Experiments 1 and 3: doubling the concentration of Br− (1.00 to 2.00 mol/dm3) makes the initial rate four times as fast (0.008 to 0.032). [1]
Experiments 2 and 4: doubling the concentration of H+ makes the initial rate twice as fast (0.016 to 0.032). [1]
As the concentration increases, there are more particles per unit volume. [1]
This increases the frequency of effective collisions between reacting particles, so the initial rate increases. [1]
The final volume of gas is lower. [1]
The initial gradient is steeper. [1]
3CaCO3 + 2H3PO4 → Ca3(PO4)2 + 3H2O + 3CO2 [1]
Moles of CaCO3 = 6100 = 0.06 mol and moles of H3PO4 = 401000 × 2 = 0.08 mol [1]
CaCO3 : H3PO4 = 3 : 2, so 0.08 mol of H3PO4 needs 0.12 mol of CaCO3, but only 0.06 mol is present. Calcium carbonate is the limiting reactant. [1]
A weak acid only partially ionises, so the concentration of H+ ions is lower. [1]
There are fewer H+ ions per unit volume. [1]
So the frequency of effective collisions decreases and the rate of reaction is lower. [1]