Pennies minted after 1982 are mostly zinc (97.5%) with a...

Pennies minted after 1982 are mostly zinc (97.5%) with a copper cover. If a post-1982 penny is dissolved in a small amount of nitric acid, the copper coating reacts as in Problem 3.90 and the exposed zinc reacts according to the following equation: $$\mathrm{Zn}(\mathrm{s})+2 \mathrm{HNO}_{3}(a q) \longrightarrow \mathrm{Zn}\left(\mathrm{NO}_{3}\right)_{2}(a q)+\mathrm{H}_{2}(g)$$ For a penny that weighs $2.482 \mathrm{g},$ what is the molarity of the $\mathrm{Zn}\left(\mathrm{NO}_{3}\right)_{2}$ if the resultant solution is diluted to 250.0 $\mathrm{mL}$ with water?

Pennies minted after 1982 are mostly zinc (97.5%) with a copper cover. If a post-1982 penny is dissolved in a small amount of nitric acid, the copper coating reacts as in Problem 3.90 and the exposed zinc reacts according to the following equation:
$$\mathrm{Zn}(\mathrm{s})+2 \mathrm{HNO}_{3}(a q) \longrightarrow \mathrm{Zn}\left(\mathrm{NO}_{3}\right)_{2}(a q)+\mathrm{H}_{2}(g)$$
For a penny that weighs $2.482 \mathrm{g},$ what is the molarity of the
$\mathrm{Zn}\left(\mathrm{NO}_{3}\right)_{2}$ if the resultant solution is diluted to 250.0 $\mathrm{mL}$ with water?

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Key Concepts

Stoichiometry

Stoichiometry is the quantitative relationship between reactants and products in a chemical reaction. It uses the balanced chemical equation to convert between masses, moles, and volumes, allowing one to predict the amount of a product (such as Zn(NO3)2) formed from a known mass of reactant (zinc).

Molarity and Dilution

Molarity is a measure of the concentration of a solution, defined as the number of moles of solute per liter of solution. Dilution involves adding solvent to a solution, which changes its concentration without altering the number of moles of solute. Calculating molarity after dilution requires dividing the moles of solute by the new total volume of the solution.

Percent Composition

This concept involves determining the amount of a specific component within a mixture or alloy by using the percentage by mass. In this context, the zinc content in a composite material (such as a penny) is found by applying the given percentage to its total weight, which is essential for calculating the amount of reactive metal.

Molar Mass and Mole Calculations

Knowing the molar mass of a substance enables the conversion between its mass and the number of moles. This conversion is critical for stoichiometric calculations because chemical equations are balanced in terms of moles rather than mass.

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