Ch.3 - Chemical Reactions and Reaction Stoichiometry

Problem 112

Chapter 3, Problem 112

A 3.50 g of an alloy which contains only lead and tin is dissolved in hot HNO3. Excess sulfuric acid is added to this solution and 1.57g of PbSO4(s) is obtained. (b) Assuming all the lead in the alloy reacted to form PbSO4, what was the amount, in grams, of lead and tin in the alloy respectively?

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Identify the chemical reaction: Lead (Pb) reacts with sulfuric acid (H2SO4) to form lead sulfate (PbSO4).

Use the mass of PbSO4 obtained (1.57 g) to calculate the moles of PbSO4 using its molar mass.

Since the stoichiometry of the reaction is 1:1, the moles of PbSO4 will be equal to the moles of Pb in the alloy.

Convert the moles of Pb to grams using the molar mass of lead.

Subtract the mass of lead from the total mass of the alloy to find the mass of tin.

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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 conservation of mass. It involves using balanced chemical equations to determine the relationships between the amounts of substances consumed and produced. In this question, stoichiometry is essential for relating the mass of PbSO4 produced to the mass of lead in the original alloy.

Molar Mass

Molar mass is the mass of one mole of a substance, typically expressed in grams per mole (g/mol). It is crucial for converting between the mass of a substance and the number of moles, which allows for stoichiometric calculations. For this problem, knowing the molar masses of lead (Pb) and tin (Sn) will help determine the amounts of each metal in the alloy.

Chemical Reactions and Precipitation

Chemical reactions involve the transformation of reactants into products, and precipitation occurs when a solid forms from a solution. In this scenario, the formation of PbSO4 as a precipitate indicates that lead from the alloy reacted with sulfate ions. Understanding this process is key to determining how much lead was present in the original alloy based on the mass of the precipitate formed.

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