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Chapter 4: Problem 129

Lead nitrate and potassium iodide react in aqueous solution to form a yellow precipitate of lead iodide. In one series of experiments, the masses of the two reactants were varied, but the total mass of the two was held constant at \(5.000 \mathrm{g}\). The lead iodide formed was filtered from solution, washed, dried, and weighed. The table gives data for a series of reactions. $$\begin{array}{lll} \hline & \text { Mass of Lead } & \text { Mass of Lead } \\ \text { Experiment } & \text { Nitrate, } g & \text { lodide, } g \\ \hline 1 & 0.500 & 0.692 \\ 2 & 1.000 & 1.388 \\ 3 & 1.500 & 2.093 \\ 4 & 3.000 & 2.778 \\ 5 & 4.000 & 1.391 \\ \hline \end{array}$$ (a) Plot the data in a graph of mass of lead iodide versus mass of lead nitrate, and draw the appropriate curve(s) connecting the data points. What is the maximum mass of precipitate that can be obtained? (b) Explain why the maximum mass of precipitate is obtained when the reactants are in their stoichiometric proportions. What are these stoichiometric proportions expressed as a mass ratio, and as a mole ratio? (c) Show how the stoichiometric proportions determined in part (b) are related to the balanced equation for the reaction.

Short Answer

Expert verified
The maximum mass of the precipitate is obtained when the reactants are in their stoichiometric proportions because that's when all the reactants can fully react to produce the maximum possible amount of product. The stoichiometric proportions, expressed as a mass ratio and a mole ratio, can be calculated from the data at this point. These ratios should match with the coefficients in the balanced chemical equation for the reaction.

Step by step solution

01

Plot the data

Use the given data to plot a graph of mass of lead iodide (on the y-axis) against mass of lead nitrate (on the x-axis). Draw the curve that connects the data points.
02

Determine the maximum mass of precipitate

Look at the graph and find the highest point on the curve - this represents the maximum mass of lead iodide that can be obtained.
03

Explain why maximum mass of precipitate is obtained at stoichiometric proportions

The maximum mass of precipitate is obtained when the reactants are in their stoichiometric proportions because this is the point at which all the reactants are fully used up in the reaction, leading to the optimal amount of product.
04

Calculate the mass ratio

Find the stoichiometric proportions expressed as a mass ratio by dividing the mass of lead nitrate at which the maximum mass of lead iodide is formed by the mass of lead iodide obtained.
05

Calculate the mole ratio

Convert the masses of both lead nitrate and lead iodide to moles by dividing each by their respective molar masses. The ratio of these two values is the stoichiometric proportions expressed as a mole ratio.
06

Relate the stoichiometric proportions to the balanced equation

In the balanced equation for the reaction, the coefficients of the reactants and products represent the mole ratio in which they react/are formed. Verify that this ratio matches the mole ratio calculated in step 5 to demonstrate how the stoichiometric proportions are related to the balanced chemical equation.

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Most popular questions from this chapter

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