2.40 g of magnesium (Ar = 24.0) reacts with excess hydrochloric acid. What volume of hydrogen forms at room temperature and pressure (24.0 dm3 mol-1)?
Answer and explanation
Correct answer: D. 2.40 dm3
- Step 1: Mg + 2HCl -> MgCl2 + H2, so the Mg:H2 ratio is 1:1. Step 2. Moles Mg , so moles H2 . Step 3. Volume dm3. Answer: 2.40 dm3. Why not the others: 1.20 assumes a 2:1 ratio of magnesium to hydrogen; 4.80 assumes 1:2; 24.0 is the molar volume itself.
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