Final answer:
To determine the number of moles of H₂ that can be formed when a 2.78 g sample of Mg reacts with excess HCl, use the balanced chemical equation and the molar mass of Mg to calculate the number of moles of Mg. Since 1 mole of Mg reacts with 1 mole of H₂, the number of moles of H₂ formed will also be equal to the number of moles of Mg.
Step-by-step explanation:
To determine the number of moles of H₂ that can be formed when a 2.78 g sample of Mg reacts with excess HCl, you need to use the balanced chemical equation and the molar mass of Mg.
The balanced chemical equation for the reaction between Mg and HCl is: Mg(s) + 2 HCl(aq) → MgCl₂(aq) + H₂(g)
From the balanced chemical equation, you can see that 1 mole of Mg reacts with 2 moles of HCl to produce 1 mole of H₂. Using the molar mass of Mg (24.305 g/mol), you can calculate the number of moles of Mg in the sample: 2.78 g Mg / 24.305 g/mol = 0.114 moles of Mg
Since 1 mole of Mg reacts with 1 mole of H₂, the number of moles of H₂ formed will also be 0.114 moles.