Ch.4 - Chemical Quantities & Aqueous Reactions

Problem 31

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Chapter 4, Problem 31

Hydrobromic acid dissolves solid iron according to the reaction:
Fe(s) + 2 HBr(aq) → FeBr₂(aq) + H₂(g)
What mass of HBr (in g) do you need to dissolve a 3.2-g pure iron bar on a padlock? What mass of H₂ would the complete reaction of the iron bar produce?

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Determine the molar mass of iron (Fe) and hydrobromic acid (HBr).

Calculate the number of moles of iron in the 3.2-g iron bar using its molar mass.

Use the stoichiometry of the balanced chemical equation to find the moles of HBr needed. The equation shows that 1 mole of Fe reacts with 2 moles of HBr.

Convert the moles of HBr to grams using the molar mass of HBr.

Calculate the moles of H2 produced using the stoichiometry of the reaction, where 1 mole of Fe produces 1 mole of H2, and then convert this to grams using the molar mass of H2.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Stoichiometry

Stoichiometry is the calculation of reactants and products in chemical reactions based on the balanced chemical equation. It allows us to determine the relationships between the amounts of substances involved in a reaction, using mole ratios derived from the coefficients in the balanced equation. In this case, it helps us find the mass of HBr needed to react with a given mass of iron and the mass of hydrogen gas produced.

Molar Mass

Molar mass is the mass of one mole of a substance, typically expressed in grams per mole (g/mol). It is essential for converting between the mass of a substance and the number of moles, which is necessary for stoichiometric calculations. For this problem, knowing the molar masses of iron (Fe) and hydrobromic acid (HBr) will allow us to calculate the required mass of HBr and the mass of hydrogen gas produced.

Gas Laws

Gas laws describe the behavior of gases under various conditions of temperature and pressure. In this context, while the production of hydrogen gas (H2) is a result of the reaction, understanding gas laws can help predict how the gas behaves after formation. Although not directly required for mass calculations, it provides insight into the properties of the gas produced in the reaction.

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Combined Gas Law

Related Practice

Calculate how many moles of NH₃ form when each quantity of reactant completely reacts. 3 N₂H₄(l) → 4 NH₃(g) + N₂(g) c. 65.3 g N₂H₄

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Textbook Question

Consider the balanced equation:

SiO₂(s) + 3 C(s) → SiC(s) + 2 CO(g)

Complete the table showing the appropriate number of moles of reactants and products. If the number of moles of a reactant is provided, fill in the required amount of the other reactant, as well as the moles of each product that forms. If the number of moles of a product is provided, fill in the required amount of each reactant to make that amount of product, as well as the amount of the other product that forms.

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Textbook Question

Consider the balanced equation:

SiO₂(s) + 3 C(s) → SiC(s) + 2 CO(g)

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Textbook Question

Hydrobromic acid dissolves solid iron according to the reaction:

Fe(s) + 2 HBr(aq) → FeBr₂(aq) + H₂(g)

What mass of HBr (in g) do you need to dissolve a 3.2-g pure iron bar on a padlock?

3885

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Textbook Question

Sulfuric acid dissolves aluminum metal according to the reaction:

2 Al(s) + 3 H₂SO₄(aq) → Al₂(SO₄)₃(aq) + 3 H₂( g)

Suppose you want to dissolve an aluminum block with a mass of 15.2 g. What minimum mass of H₂SO₄ (in g) do you need? What mass of H₂ gas (in g) does the complete reaction of the aluminum block produce?

For each of the reactions, calculate the mass (in grams) of the product that forms when 3.67 g of the underlined reactant completely reacts. Assume that there is more than enough of the other reactant. a. Ba(s) + Cl2(g) → BaCl2(s) b. CaO(s) + CO2(g) → CaCO3(s) c. 2 Mg(s) + O2(g) → 2 MgO(s) d. 4 Al(s) + 3 O2(g) → 2 Al2O3(s)

Hydrobromic acid dissolves solid iron according to the reaction:Fe(s) + 2 HBr(aq) → FeBr2(aq) + H2(g)What mass of HBr (in g) do you need to dissolve a 3.2-g pure iron bar on a padlock? What mass of H2 would the complete reaction of the iron bar produce?

Verified Solution

Key Concepts

Stoichiometry

Molar Mass

Gas Laws

Hydrobromic acid dissolves solid iron according to the reaction:
Fe(s) + 2 HBr(aq) → FeBr₂(aq) + H₂(g)
What mass of HBr (in g) do you need to dissolve a 3.2-g pure iron bar on a padlock? What mass of H₂ would the complete reaction of the iron bar produce?