Final answer:
To find the mass of HBr needed to dissolve a 4.3-g pure iron bar, you calculate the moles of iron and use stoichiometry to determine the moles and then the mass of HBr required. The calculation suggests that 12.46 grams of HBr are needed, but this does not match the provided options, indicating a potential error in the question.
Step-by-step explanation:
The student is asking for the mass of HBr needed to dissolve a 4.3-g pure iron bar based on a chemical reaction. To solve this, we first need the balanced chemical equation for the reaction between iron (Fe) and hydrobromic acid (HBr), which is typically:
Fe(s) + 2 HBr(aq) → FeBr₂(aq) + H₂(g).
This tells us that each mole of Fe reacts with 2 moles of HBr. Using the molar mass of Fe (55.85 g/mol) to convert the mass of iron to moles, we find:
(4.3 g Fe) / (55.85 g/mol Fe) = 0.077 moles Fe.
Since it takes 2 moles of HBr for every mole of Fe, we need:
0.077 moles Fe * 2 moles HBr/mole Fe = 0.154 moles HBr.
The molar mass of HBr is approximately 80.91 g/mol. To find the mass of HBr required, we multiply the number of moles by the molar mass:
0.154 moles HBr * 80.91 g/mol = 12.46 g HBr.
However, none of the options provided (A, B, C, D) match this calculation, suggesting a typo or mistake in the options given or in the initial question. The student should double-check all variables and the source of the question for possible errors.