Question

What is the Molarity (M) of the HCl solution if 250 mL of the HCl solution reacts with magnesium to produce 4.20 L of H2 gas measured at 760 mmHg and 0 Celsius? Use the following unbalanced equation:
Mg (s) + HCl (aq) --> MgCl2 (aq) + H2 (g)

I balanced the equation to:
Mg (s) + 2HCl --> MgCl2 (aq) + H2 (g)

I think I start with the 4.20 L H2 and convert using (STP) 22.4 L H2= 1 mol H2... and then I'm stuck.

Answer 1

ok so you start with:

n= V/Vm

and you get that

n(H2) = 0,1875 mol

now you get the ratio from the equation

n(HCl)/n(H2) = 2/1 = 2

so

n(HCl) = 2 * n(H2) = 0,375 mol

now you just use:

c=n/V

c(HCl) = 0,375 mol / 250 * 10^-3 dm^3 = 1,5 M

Answer 2

Thank you!

Answer 3

not a problem :)