What volume of hydrogen is produced when 12g or magnesium is added to excess HCl(aq)?

Question

please could you show working so i can work out similar questions.

thanks

Answer 1

first you have to write the equation and balance it:
Mg+2HCl---->MgCl2+H2

then you also have to know that, in standard conditions, the volume of one mole of any gas is 22,4 L

you know the molar weight of magnesium=24 and, as the equation says, from each mole of Mg you obtain 1 mole of H2, that is 22.4L of H2, and you know that 12g of magnesium are used:

24gMg............22,4L H2
12gMg............xL H2.

x=12*22,4/24=11,2Lof H2 obtained

hope it was clear enough. cheers:)

Answer 2

12g of magnesium is half a mole of Mg - divide the mass by the Ar of magnesium - and the balanced chemical equation tells us that for every moles of Mg, we get a mole of H2. So we are going to get half a mole of H2, which is 11.2 litres at STP.

Mg + 2HCl ----> MgCl2 + H2.