Question

(a) A strontium hydroxide solution is prepared by dissolving \(10.45 \mathrm{~g}\) 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 \(31.5 \mathrm{~mL}\) aliquot of the nitric acid solution, what is the concentration (molarity) of the acid?

Short answer

The molarity of the strontium hydroxide solution is \(0.862 \mathrm{~M}\). 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 \(1.11 \mathrm{~M}\).

Step-by-step solution

1. Calculate the molarity of strontium hydroxide solution (

To find the molarity, we need to divide the moles of solute (strontium hydroxide) by the volume of the solution in liters. First, we'll convert the mass of strontium hydroxide into moles using its molar mass, and then divide it by the volume of the solution in liters. Molarity = moles of solute / volume of solution in liters Moles of Sr(OH)2 = (10.45 g) / (121.64 g/mol) (molar mass of Sr(OH)2 = 121.64 g/mol) Volume of solution = 50.00 mL = 0.050 L Molarity = moles of Sr(OH)2 / 0.050 L)

2. Balanced chemical equation for the reaction between strontium hydroxide and nitric acid (

Based on the information given, we know that strontium hydroxide reacts with nitric acid to produce strontium nitrate and water. To find the balanced chemical equation, we need to ensure that the reactants and products have the same number of atoms of each element. Sr(OH)2 + 2HNO3 -> Sr(NO3)2 + 2H2O

3. Calculate the concentration of the nitric acid solution (

We are given information on the volume of strontium hydroxide solution required to neutralize a certain volume of the nitric acid solution. We can use stoichiometry and the balanced chemical equation to find the molarity of the nitric acid solution. 1. Calculate the moles of Sr(OH)2 used in the titration: moles of Sr(OH)2 = molarity of Sr(OH)2 * volume of Sr(OH)2 used = (molarity calculated in step 1) * (23.9 mL) * (1 L / 1000 mL) 2. Use stoichiometry to find the moles of HNO3: 1 mol Sr(OH)2 reacts with 2 mol HNO3, so moles of HNO3 = 2 * moles of Sr(OH)2 3. Calculate the molarity of HNO3: Molarity of HNO3 = moles of HNO3 / volume of HNO3 in liters = moles of HNO3 / (31.5 mL * (1 L / 1000 mL))

Key concepts

Titration

Titration is a laboratory technique used to determine the concentration of an unknown solution by reacting it with a solution of known concentration, referred to as the titrant. The point at which the reaction is complete is called the equivalence point, and it can often be detected by a color change with the aid of an indicator or by measuring pH. In the given exercise, strontium hydroxide is used as the titrant to find the concentration of nitric acid. By carefully measuring the volume of strontium hydroxide needed to neutralize the nitric acid, the concentration of the latter can be determined through calculation, a foundation of the titration process.

Stoichiometry

Stoichiometry is the section of chemistry that deals with the calculation of the quantities of reactants and products involved in chemical reactions. It is based on the law of conservation of mass, which states that matter is neither created nor destroyed in a chemical reaction. Stoichiometry utilizes the coefficients from a balanced chemical equation to determine the relative amounts of substances needed or produced. In the context of the given exercise, stoichiometry allows us to calculate the moles of nitric acid that reacted with strontium hydroxide, using the known molarity of the strontium hydroxide and the volume used in the titration.

Understanding the Mole Ratio

The mole ratio is taken from the coefficients of the reactants and products in the balanced chemical equation. For instance, the equation from the exercise indicates that 1 mole of Sr(OH)2 reacts with 2 moles of HNO3. This ratio is essential to find the moles and, subsequently, the molarity of the nitric acid solution.

Balanced Chemical Equation

A balanced chemical equation is one that obeys the law of conservation of mass, with an equal number of atoms for each element on both the reactant and product sides of the equation. The process of balancing an equation involves adjusting the coefficients, which are numbers placed before the chemical formulas, to get the same number of atoms of each element on both sides. The balanced equation provides the mole ratios of reactants and products, as seen in the exercise with the reaction of strontium hydroxide with nitric acid. These mole ratios are used in stoichiometry to calculate the amounts of reactants used and products formed.

Significance in Calculations

The significance of a balanced equation can't be overstated, as it is fundamental to stoichiometric calculations. The exercise presents the equation Sr(OH)2 + 2HNO3 -> Sr(NO3)2 + 2H2O, which tells us that for every mole of strontium hydroxide that reacts, two moles of nitric acid are required. This molar relationship is key to determining the correct stoichiometry and hence the concentration of an unknown solution during a titration.