A procedure for determining the amount of iron in a sample is to convert the iron to Fe2+ and then titrate it with a solu-tion of Ce(NH4)2(NO3)6: What is the mass percent of iron in a sample if 1.2284 g of the sample requires 54.91 mL of 0.1018 M Ce(NH4)2(NO3)6 for complete reaction?

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Identify the balanced chemical equation for the reaction between Fe^{2+} and Ce(NH4)_2(NO3)_6. The reaction is: \[ \text{Fe}^{2+} + \text{Ce}^{4+} \rightarrow \text{Fe}^{3+} + \text{Ce}^{3+} \]

Calculate the moles of Ce^{4+} used in the titration. Use the formula: \[ \text{moles of Ce}^{4+} = \text{Molarity} \times \text{Volume (L)} \]

Since the reaction is a 1:1 stoichiometry, the moles of Fe^{2+} will be equal to the moles of Ce^{4+}. Therefore, the moles of Fe^{2+} = moles of Ce^{4+}.

Calculate the mass of iron (Fe) using the moles of Fe^{2+} and the molar mass of iron (55.85 g/mol). Use the formula: \[ \text{mass of Fe} = \text{moles of Fe} \times \text{molar mass of Fe} \]

Determine the mass percent of iron in the sample using the formula: \[ \text{mass percent of Fe} = \left( \frac{\text{mass of Fe}}{\text{mass of sample}} \right) \times 100\% \]

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주요 개념

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Titration

Titration is a quantitative analytical technique used to determine the concentration of a solute in a solution. In this process, a solution of known concentration (the titrant) is gradually added to a solution of unknown concentration until the reaction reaches its endpoint, indicated by a color change or other measurable signal. This method is essential for calculating the amount of a specific substance, such as iron in this case, based on the volume and concentration of the titrant used.

Molarity

Molarity is a measure of concentration defined as the number of moles of solute per liter of solution. It is expressed in moles per liter (mol/L) and is crucial for stoichiometric calculations in titrations. In the given problem, the molarity of the cerium solution (0.1018 M) is used to determine how many moles of cerium react with the iron, allowing for the calculation of the mass percent of iron in the sample.

Mass Percent

Mass percent is a way of expressing the concentration of a component in a mixture, calculated as the mass of the component divided by the total mass of the mixture, multiplied by 100. This concept is important for determining the proportion of iron in the sample after the titration, as it provides a clear understanding of how much of the sample's mass is attributable to iron, which is essential for evaluating the sample's quality or compliance with specifications.