5.6 g of pure iron was dissolved in 100 ml of 10% hydrochloric acid solution (p = 1.05 g / ml).

5.6 g of pure iron was dissolved in 100 ml of 10% hydrochloric acid solution (p = 1.05 g / ml). Calculate the mass fraction of hydrogen chloride in the resulting solution.

Let’s write the reaction equation:

Fe + 2HCl → FeCl2 + H2 (iron (II) chloride, hydrogen).

n (Fe) = m (Fe) / M (Fe) = 5.6 g / 56 g / mol = 0.1 mol.

Find the mass of the hydrochloric acid solution and the mass of the solute:

mr-ra (HCl) = Vr-ra (HCl) * pp-ra (HCl) = 100 ml * 1.05 g / ml = 105 g.

mr.w. (HCl) = (mr-pa (HCl) * w.w.) / 100% = (105 g * 10%) / 100% = 10.5 g.

Let’s find the amount of acid substance:

n (HCl) = m (HCl) / M (HCl) = 10.5 g / 36.5 g / mol = 0.288 mol.

For 0.1 mol of Fe, 0.2 mol of HCl is required, which means there is an excess of acid, we are calculating for iron.

Let’s find the mass of the resulting solution:

n (H2) = n (Fe) = 0.1 mol.

m (H2) = n (H2) * M (H2) = 0.1 mol * 2 g / mol = 0.2 g.

mr-ra = m (Fe) + mr-ra (HCl) – m (H2) = 5.6 g + 105 g – 0.2 g = 110.4 g.

Find the mass of the remaining acid:

0.088 mol of acid has not reacted, which means

bres (HCl) = nres (HCl) * M (HCl) = 0.088 mol * 36.5 g / mol = 3.212 g.

Let’s find the mass fraction of the acid:

w (HCl) = (m (HCl) * 100%) / mp-pa = (3.212 g * 100%) / 110.4 g = 2.91%.