16. Magnesium metal reacts with HCl solution, liberating H2 gas and generating M

Question

16. Magnesium metal reacts with HCl solution, liberating H2 gas and generating Mg2+ cations in solution. A 1.695-g sample of Mg metal is added to 125.0 mL of a 4.00 M HCl solution, and the reaction goes to completion. What mass of H2 is formed?

Explanation / Answer

Mg(s) + 2HCl ----> MgCl2 + H2 1.695g Mg / 24.312 g/mol Mg = 0.0697186 moles Mg (0.1250 L )x(4.00M HCl)= 0.500 moles HCl According to the balanced equation for every 1 mol of Mg you need 2 moles of HCl. Since you have 0.04236 mol Mg you would need 0.08472 mols of HCl and you have 0.500 moles which is more than enough. This means you have excess HCl and the amount of H2 liberated will depend only on the amount of Mg you used so...to get the grams of H2 you would get. 0.0697186 mols Mg x ( 1 mol H2/1 mol Mg) x (2.01594 g H2 / 1 mol H2) gives you 0.1405486 g H2

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