Reaction with metals

3 marks · Normal

A student reacts 4.8 g of magnesium ribbon with excess ethanoic acid. Magnesium reacts with ethanoic acid as shown:

Calculate the maximum volume of hydrogen gas produced at room temperature and pressure (rtp), assuming 1 mole of gas occupies 24 dm³. (Relative atomic mass: Mg = 24)

Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.

Show answer

4.8 dm³ (±0.1)

Also accept: 4.8 dm3; 4.80 dm3

Common mistakes: Dividing by 2 for H2 moles by mistake; Not converting g to moles

Show mark scheme and worked solution

Marking points

M1 · 1 mark · Calculate moles of magnesium used:

M2 · 1 mark · Relate moles of Mg to moles of H2 produced using the 1:1 molar ratio from the equation; so moles H2 = 0.2 (follow-through)

A1 · 1 mark · Calculate volume of H2 produced: (follow-through)

Worked solution

Step 1: Calculate moles of magnesium used:

Step 2: From the balanced equation, 1 mole of Mg produces 1 mole of H₂.

So, moles of hydrogen gas formed = 0.2 mol.

Step 3: Calculate the volume of hydrogen gas at rtp:

Final answer: 4.8 dm³