At STP how many grams of Mg are required to produce 245 mL of H₂ in the reaction shown below? Mg(s)+ 2 HCl(aq)→ H₂(g)+ MgCl₂(aq) A)245 g B)0.266 g C)0.245 g D)29 g

Question

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First, we need to identify the gas produced, which is H₂. At STP, 1 mole of any gas occupies 22.4 L. Therefore, 245 mL (or 0.245 L) of H₂ is 0.245 L / 22.4 L/mol = 0.01094 moles of H₂. The balanced equation shows a 1:1 mole ratio between Mg and H₂, so 0.01094 moles of Mg are also required. The molar mass of Mg is approximately 24.305 g/mol, so the mass of Mg needed is 0.01094 moles * 24.305 g/mol = 0.266 g.

At STP How Many Grams of Mg Are Required to Produce