An impure sample of zinc (Zn) is treated with an excess of...

An impure sample of zinc (Zn) is treated with an excess of sulfuric acid $\left(\mathrm{H}_{2} \mathrm{SO}_{4}\right)$ to form zinc sulfate $\left(\mathrm{ZnSO}_{4}\right)$ and molecular hydrogen $\left(\mathrm{H}_{2}\right) .$ (a) Write a balanced equation for the reaction. (b) If $0.0764 \mathrm{~g}$ of $\mathrm{H}_{2}$ is obtained from $3.86 \mathrm{~g}$ of the sample, calculate the percent purity of the sample. (c) What assumptions must you make in (b)?

An impure sample of zinc (Zn) is treated with an excess of sulfuric acid $\left(\mathrm{H}_{2} \mathrm{SO}_{4}\right)$ to form zinc sulfate $\left(\mathrm{ZnSO}_{4}\right)$ and molecular hydrogen $\left(\mathrm{H}_{2}\right) .$
(a) Write a balanced equation for the reaction.
(b) If $0.0764 \mathrm{~g}$ of $\mathrm{H}_{2}$ is obtained from $3.86 \mathrm{~g}$ of the sample, calculate the percent purity of the sample.
(c) What assumptions must you make in (b)?

Key Concepts

Balanced Chemical Equations

A balanced chemical equation represents the conservation of mass, ensuring that the number of atoms for each element is the same on both sides of the reaction. It is critical in stoichiometric calculations since the coefficients in the equation define the mole ratio of reactants and products involved in the reaction.

Stoichiometry

Stoichiometry involves using the relationships between the quantities of reactants and products as defined by the balanced chemical equation. It allows one to predict yields, calculate the amounts of substances needed or produced, and understand the conversion factors between different chemical species.

Percent Purity Calculation

The percent purity calculation is a method used to determine the fraction or percentage of a desired component within an impure sample. By comparing the amount of a product formed (as determined through stoichiometric relationships) to the theoretical yield, one can assess the purity of the starting material.

Assumptions in Quantitative Analysis

Quantitative chemical analysis often relies on idealized assumptions, such as the complete reaction of the pure component, the absence of side reactions, and the accurate measurement of experimental quantities. These assumptions simplify the calculation and interpretation of results, but they must be justified or acknowledged as limitations in real experimental conditions.

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