Ch.4 - Reactions in Aqueous Solution

Brown - Chemistry: The Central Science 15th Edition

Brown15th EditionChemistry: The Central ScienceISBN: 9780137542970Not the one you use?Change textbook

Brown 15th Edition

Ch.4 - Reactions in Aqueous Solution

Problem 89

Chapter 4, Problem 89

A 0.5895-g sample of impure magnesium hydroxide is dissolved in 100.0 mL of 0.2050 M HCl solution. The excess acid then needs 19.85 mL of 0.1020 M NaOH for neutralization. Calculate the percentage by mass of magnesium hydroxide in the sample, assuming that it is the only substance reacting with the HCl solution.

Verified step by step guidance

Calculate the moles of HCl initially present using the concentration and volume: \( \text{moles of HCl} = 0.2050 \, \text{M} \times 0.1000 \, \text{L} \).

Calculate the moles of NaOH used in the neutralization of excess HCl: \( \text{moles of NaOH} = 0.1020 \, \text{M} \times 0.01985 \, \text{L} \).

Since NaOH neutralizes the excess HCl in a 1:1 ratio, the moles of excess HCl are equal to the moles of NaOH used.

Subtract the moles of excess HCl from the initial moles of HCl to find the moles of HCl that reacted with magnesium hydroxide.

Use the stoichiometry of the reaction \( \text{Mg(OH)}_2 + 2\text{HCl} \rightarrow \text{MgCl}_2 + 2\text{H}_2\text{O} \) to find the moles of \( \text{Mg(OH)}_2 \) that reacted, then calculate the mass of \( \text{Mg(OH)}_2 \) and determine the percentage by mass in the sample.

Verified video answer for a similar problem:

This video solution was recommended by our tutors as helpful for the problem above.

Video duration:

12m

Was this helpful?

Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Stoichiometry

Stoichiometry is the calculation of reactants and products in chemical reactions based on the balanced chemical equation. It allows us to determine the amount of a substance consumed or produced in a reaction. In this question, stoichiometry is essential for relating the moles of HCl reacted with magnesium hydroxide to the moles of NaOH used for neutralization.

Molarity

Molarity is a measure of concentration defined as the number of moles of solute per liter of solution. It is crucial for calculating the amount of acid and base involved in the reaction. In this problem, the molarity of HCl and NaOH solutions is used to find the moles of each reactant, which are necessary for determining the mass percentage of magnesium hydroxide.

Mass Percentage

Mass percentage 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. In this scenario, calculating the mass percentage of magnesium hydroxide involves determining the mass of magnesium hydroxide that reacted with HCl and comparing it to the total mass of the impure sample.

Related Practice

Textbook Question

The accompanying photo shows the reaction between a solution of Cd(NO₃)₂ and one of Na₂S. (b) What ions remain in solution?

354

views

Textbook Question

A solution is made by mixing 15.0 g of Sr(OH)2 and 55.0 mL of 0.200 M HNO3. b. Calculate the concentration of each ion remaining in solution.

views

Textbook Question

A solution of 100.0 mL of 0.200 M KOH is mixed with a solution of 200.0 mL of 0.150 M NiSO_4.(b) What precipitate forms?

383

views

Textbook Question

A solution is made by mixing 15.0 g of Sr(OH)2 and 55.0 mL of 0.200 M HNO3. c. Is the resulting solution acidic or basic?

Textbook Question

A 1.248-g sample of limestone rock is pulverized and then treated with 30.00 mL of 1.035 M HCl solution. The excess acid then requires 11.56 mL of 1.010 M NaOH for neutralization. Calculate the percentage by mass of calcium carbonate in the rock, assuming that it is the only substance reacting with the HCl solution.

1098

views