Help my fellow classmates with this question please

Question

At constant temperature and pressure, 1.25 mol of hydrogen gas occupies 28 L at STP. What amount of hydrogen gas must be removed from the volume to become 11.2 L at STP?

a) 0.13 mol
b) 0.25 mol
c) 0.50 mol
d) 0.75 mol
e) 1.00 mol

 

Pick the right answer. 

Answer 1

Hello Karen

Use avogadro's law equation, which is V₁ / n₁ = V₂ / n₂. Rearrange to solve for n₂.

n₂ = V₂ n₁ / V₁

         11.2 L x 1.25 mol
     =  -------------------------
                  28 L

     = 0.50 mol

0.50 mol of H₂ gas remains after decreasing the volume from 28 L to 11.2 L. However, the question is asking how many moles of H₂ "must be removed" for the volume to decrease.

Therefore, 1.25 - 0.50 = 0.75 mol H₂ must be removed. Answer choice d).