Question

When 0.274g of impure iron is reacted with an excess of hydrochloric acid, HCl, and 8.54 x 10^(-1) g of H2 gas is evolved, calculate the percentage of iron in the sample.

a) 87.11%
b) 78.45%
c) 64.32%
d) 92.53%

Answer 1

The percentage of iron in the sample is calculated by using stoichiometry to find the moles of iron that reacted to produce the measured hydrogen gas, converting it to mass, and then dividing by the total impure mass of the sample. The result is approximately 87.11%, which is option a).

Step-by-step explanation:

To calculate the percentage of iron in the sample, we can first write the chemical reaction of iron with hydrochloric acid that produces hydrogen gas:

Fe(s) + 2HCl(aq) → FeCl2(aq) + H2(g)

According to the reaction, one mole of iron produces one mole of hydrogen gas. Using the molar mass of iron (55.845 g/mol) and hydrogen (2.016 g/mol), we can determine the moles of hydrogen gas evolved:

Moles of H2 = Mass of H2 / Molar mass of H2
Moles of H2 = 0.854 g / 2.016 g/mol
This equals the moles of Fe reacted since the mole ratio is 1:1. Using the moles of Fe, we can calculate the mass of pure Fe that reacted:

Mass of Fe = Moles of Fe × Molar mass of Fe

Finally, we can find the percentage of iron in the sample by dividing the mass of pure Fe by the mass of the impure sample and multiplying by 100%:

Percentage of Fe = (Mass of pure Fe / Mass of impure sample) × 100%
Inserting the values into the calculations, we find the percentage of iron in the sample to be approximately 87.11%, which corresponds to option a).