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27 August, 03:30

When active metals such as magnesium are immersed in acid solution, hydrogen gas is evolved. Calculate the volume of H2 (g) at 30.1°C and 0.85 atm that can be formed when 275 mL of 0.725 M HCl solution reacts with excess Mg to give hydrogen gas and aqueous magnesium chloride.

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  1. 27 August, 06:41
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    The volume of H₂ (g) obtained is 22.4L

    Explanation:

    First of all, think the reaction:

    2HCl (aq) + Zn (s) → ZnCl₂ (aq) + H₂ (g)

    You have to add a 2, in the HCl to get ballanced.

    Now we should know how many moles of each reactant, do we have.

    Volume. Molarity = moles

    Notice that volume is in mL, so I must convert to L.

    275 mL = 0.275L

    0.275L. 0.725mol/L = 0.2 moles of HCl

    Molar mass of Zn: 65.41 g/m

    50 g / 65.41 g/m = 0.764 moles

    Ratio between reactants is 2:1, so I need the double of moles of HCl to react, and a half moles of Zn to react.

    My limiting reactant is the HCl, for 0.764 moles of Zinc, I need 1.528 (0.764.2) of HCl, and I only have 0.2 moles.

    Ratio between HCl and H₂ is 1:1, so 0.2 HCl make 0.2 moles of gas

    Now apply the Ideal Gas Law, to find out the volume

    P. V = n. R. T

    2 atm. V = 0.2 mol. 0.08206L atm/K mol. 273K

    V = (0.2 mol. 0.08206L atm/K mol. 273K) / 2 atm

    V = 2.24 L
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