reaction can go in both directions. Therefore, only some methanoic acid molecules form $\\text{H}^+$ ions in water: the acid **partially ionises**. This earns **A1** and is why methanoic acid is a weak acid.","highlights":[{"text":"Explain how the equation shows that methanoic acid is a weak acid.","location":"specification"}]}]}],"generatedAt":"2026-07-21T03:09:07.244Z","modelVersion":"gpt-5.6-terra","explanationVersion":"v3"},"options":[]},{"id":"a83046ec-b8fe-4c8a-af8f-a54f66b4073a","label":"c","content":"A student adds a solution of methanoic acid to excess calcium carbonate in an open beaker on a digital balance.\n\nExplain what happens to the mass of the beaker and its contents during the reaction.","markscheme":"- The mass of the beaker and its contents decreases B1\n- Because carbon dioxide ($CO_2$) gas is produced/evolved M1\n- The gas escapes from the open beaker A1","marks":3,"order":2,"markingRubric":null,"explanation":{"methods":[{"id":"track_mass_change","label":"Track the mass change","steps":[{"type":"text","order":0,"title":"State the mass change","content":"The mass of the beaker and its contents **decreases** during the reaction. This is the first marking point (B1).","highlights":[{"text":"Explain what happens to the mass of the beaker and its contents during the reaction.","location":"specification"}]},{"type":"text","order":1,"title":"Identify the gas","content":"Methanoic acid reacts with calcium carbonate and produces carbon dioxide gas, $\\mathrm{CO_2}$. This earns the explanation mark (M1).","highlights":[{"text":"methanoic acid to excess calcium carbonate","location":"specification"}]},{"type":"text","order":2,"title":"Let the gas escape","content":"The beaker is open, so the carbon dioxide escapes into the air rather than remaining on the balance. This earns the final mark (A1) and explains the decrease in measured mass.","highlights":[{"text":"in an open beaker on a digital balance","location":"specification"}]}]}],"generatedAt":"2026-07-21T03:14:43.871Z","modelVersion":"gpt-5.6-terra","explanationVersion":"v3"},"options":[]},{"id":"9118d387-d373-4638-8ebc-918f6dcfa172","label":"d","content":"The student compares the rates of reaction of calcium carbonate with:\n- \$0.01\\text{ mol/dm}^3\$ methanoic acid\n- \$0.01\\text{ mol/dm}^3\$ ethanoic acid\n\nThe rate of the reaction with methanoic acid is greater than the rate of the reaction with ethanoic acid.\n\nExplain why.\n\nYou should refer to ions in your answer and use information from Table 1.","markscheme":"- Table 1 shows that methanoic acid has a lower pH than ethanoic acid B1\n- A lower pH indicates a higher concentration of hydrogen ions ($H^+$) M1\n- This leads to a higher frequency of successful collisions (more collisions per unit time) between $H^+$ ions and carbonate particles A1","marks":3,"order":3,"markingRubric":null,"explanation":{"methods":[{"id":"ion_collision_explanation","label":"Link pH to collision frequency","steps":[{"type":"text","order":0,"title":"Compare the pH values","content":"Both acids have the same concentration, so use Table 1 to compare their pH values. Methanoic acid has pH $2.91$, which is lower than ethanoic acid’s pH $3.39$. This earns **B1**.","highlights":[{"text":"The rate of the reaction with methanoic acid is greater than the rate of the reaction with ethanoic acid.","location":"specification"},{"text":"use information from Table 1","location":"specification"}]},{"type":"text","order":1,"title":"Interpret lower pH","content":"A lower pH means a higher concentration of hydrogen ions, $\\mathrm{H^+}$. Therefore, the methanoic acid solution contains more $\\mathrm{H^+}$ ions than the ethanoic acid solution. This is **M1**.","highlights":[{"text":"You should refer to ions in your answer","location":"specification"}]},{"type":"text","order":2,"title":"Explain the faster rate","content":"With more $\\mathrm{H^+}$ ions in the same volume, $\\mathrm{H^+}$ ions collide with calcium carbonate particles more often.

Organic chemistry

Question 9

Organic chemistry Questions

Organic chemistry

Question 9

Organic chemistry Questions