Question

(b) Calculate the number of moles of magnesium and sulfuric acid that reacted.

Answer 1

The moles of Mg that reacted = 0.005 moles

The moles of H₂SO₄ that reacted = 0.005 moles.

Justification: The mole ratio from the balanced equation is 1 : 1 and since the moles of H₂SO₄ (0.005 mol is less than 0.020571898 mol of Mg) is the limiting reactant, it determines when the reaction goes into completion.

Step-by-step explanation

Given:

Mass of magnesium that reacts = 0.50 g

The volume of sulfuric acid that reacts = 25 cm³

Molarity of sulfuric acid that reacts = 0.20 moldm⁻³

What to find:

The number of moles of magnesium and sulfuric acid that reacted.

Step-by-step solution:

Step 1: Write the balanced chemical equation for the reaction.

Mg + H₂SO₄ → H₂ + MgSO₄

Step 2: Convert the mass of Mg and molarity of H₂SO₄ to moles.

The mass of Mg can be converted to moles using the mole formula:

`\begin{gathered} Moles=\frac{Mass}{Molar\text{ }mass} \\ \\ Molar\text{ }mass\text{ }of\text{ }Mg=24.305\text{ }g\text{/}mol \\ \\ Moles=\frac{0.50\text{ }g}{24.305\text{ }g\text{/}mol}=0.020571898\text{ }mol \end{gathered}`

25 cm³ of 0.20 moldm⁻³ of H₂SO₄ can be converted to moles using the formula for molarity:

`\begin{gathered} Molarity=\frac{Moles}{Volume\text{ }in\text{ }dm^3} \\ \\ Moles=Molarity* Volume\text{ }in\text{ }dm^3 \\ \\ Moles=0.20\text{ }moldm^(-3)*0.025\text{ }dm^3 \\ \\ Moles=0.005\text{ }mol \end{gathered}`

Step 3: Calculate the number of moles of magnesium and sulfuric acid that reacted.

From step 2: moles of Mg = 0.020571898 mol, moles of H₂SO₄ = 0.005 mol

Using the mole ratio of Mg and H₂SO₄ from the balanced equation in step 1, that 1 mol Mg = 1 mol H₂SO₄

Therefore, the moles of Mg that reacted will be 0.005 moles, and the moles of H₂SO₄ that reacted will be 0.005 moles.

Justification: The mole ratio from the balanced equation is 1 : 1 and since the moles of H₂SO₄ (0.005 mol is less than 0.020571898 mol of Mg) is the limiting reactant, it determines when the reaction goes into completion.