Problem 103 - Chemistry: The Central Science

Question

(a) A strontium hydroxide solution is prepared by dissolving \(12.50 \mathrm{~g}\) of \(\mathrm{Sr}(\mathrm{OH})_{2}\) in water to make \(50.00 \mathrm{~mL}\) of solution. What is the molarity of this solution? (b) Next the strontium hydroxide solution prepared in part (a) is used to titrate a nitric acid solution of unknown concentration. Write a balanced chemical equation to represent the reaction between strontium hydroxide and nitric acid solutions. (c) If \(23.9 \mathrm{~mL}\) of the strontium hydroxide solution was needed to neutralize a \(37.5 \mathrm{~mL}\) aliquot of the nitric acid solution, what is the concentration (molarity) of the acid?

Step-by-Step Solution

Answer

The molarity of the strontium hydroxide solution is \(2.06 \mathrm{M}\), and the balanced chemical equation for the reaction between strontium hydroxide and nitric acid is \(\mathrm{Sr(OH)_2 + 2HNO_3 \rightarrow Sr(NO_3)_2 + 2H_2O}\). The concentration of the nitric acid solution is \(1.03 \mathrm{M}\).

Step 1: Calculate the molarity of the strontium hydroxide solution.

To do this, we need the mass of strontium hydroxide (\(12.50 \mathrm{~g}\)), the volume of the solution (\(50.0 \mathrm{~mL}\)), and its molar mass (\(121.63 \mathrm{~g/mol}\), calculated by adding the atomic masses of strontium, oxygen, and hydrogen). First, convert the volume in milliliters to liters. Then, divide the mass of strontium hydroxide by its molar mass to find the molar quantity of strontium hydroxide. Finally, divide the molar quantity by the volume in liters to find the molarity.

Step 2: Write a balanced chemical equation.

We will write the balanced chemical equation for the reaction between strontium hydroxide, \(\mathrm{Sr(OH)_2}\), and nitric acid \(\mathrm{HNO_3}\): \[\mathrm{Sr(OH)_2 + 2HNO_3 \rightarrow Sr(NO_3)_2 + 2H_2O}\] This equation shows the stoichiometry of the reaction: one mole of strontium hydroxide reacts with two moles of nitric acid, producing one mole of strontium nitrate and two moles of water.

Step 3: Calculate the concentration of the nitric acid solution.

To do this, we will use the volume of strontium hydroxide and nitric acid solutions needed to neutralize each other (23.9 mL and 37.5 mL, respectively), and the molarity of the strontium hydroxide solution found in Step 1. To find the concentration of the nitric acid solution, we can use the relationship: \[\text{Moles of strontium hydroxide} \times 2 = \text{Moles of nitric acid}\] First, convert the volume of strontium hydroxide and nitric acid into liters. Then, calculate the moles of strontium hydroxide using the molarity from Step 1 and its volume. After that, find the moles of nitric acid using the stoichiometry from the balanced chemical equation. Finally, divide the moles of nitric acid by the volume of the nitric acid solution to find its concentration.

Key Concepts

Strontium Hydroxide

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