Question

A \(25.00 \mathrm{~mL}\) sample of aqueous hydrobromic acid of unknown concentration is neutralized by \(43.28 \mathrm{~mL}\) of \(0.1001 \mathrm{M} \mathrm{NaOH}(a q)\) (a) Write a net ionic equation for this acid-base neutralization reaction. (b) How many moles of \(\mathrm{NaOH}\) did it take for the neutralization? (c) How many moles of hydrobromic acid were neutralized? (d) What is the molar concentration of the hydrobromic acid?

Short answer

(a) The net ionic equation for the acid-base neutralization reaction is: \(H^+ (aq) + OH^- (aq) \rightarrow H_2O (l)\) (b) It took \(0.004328 \ \mathrm{mol}\) of NaOH for the neutralization. (c) \(0.004328 \ \mathrm{mol}\) of hydrobromic acid was neutralized. (d) The molar concentration of the hydrobromic acid is approximately \(0.17312 \ \mathrm{M}\).

Step-by-step solution

Write the net ionic equation

First, we need to write the balanced chemical equation for the reaction between hydrobromic acid (HBr) and sodium hydroxide (NaOH): \(HBr (aq) + NaOH (aq) \rightarrow NaBr (aq) + H_2O (l)\) Now, we write the net ionic equation by removing spectator ions (Na+ in this case). Remember that aqueous HBr and NaOH will dissociate into ions in solution: \(H^+ (aq) + Br^- (aq) + Na^+ (aq) + OH^- (aq) \rightarrow Na^+ (aq) + Br^- (aq) + H_2O (l)\) The net ionic equation is then: \(H^+ (aq) + OH^- (aq) \rightarrow H_2O (l)\)

Calculate the moles of NaOH

We need to calculate the moles of NaOH added to the solution, which can be done using the given volume and molarity of NaOH: Moles of NaOH \(= Molarity \times Volume\) Moles of NaOH \(= 0.1001 \ \mathrm{M} \times 43.28 \ \mathrm{mL} \times \frac{1 \ \mathrm{L}}{1000 \ \mathrm{mL}}\) Moles of NaOH \(= 0.004328 \ \mathrm{mol}\)

Calculate the moles of hydrobromic acid neutralized

In an acid-base neutralization reaction, 1 mole of acid reacts with 1 mole of base: Moles of HBr \(= \)Moles of NaOH \(= 0.004328 \ \mathrm{mol}\)

Determine the molar concentration of hydrobromic acid

Now we can find the concentration of HBr, given its volume and the moles needed to neutralize it: Molarity \(= \frac{\text{Moles}}{\text{Volume}}\) Molarity of HBr \(= \frac{0.004328 \ \mathrm{mol}}{25.00 \ \mathrm{mL} \times \frac{1 \ \mathrm{L}}{1000 \ \mathrm{mL}} }\) Molarity of HBr \(= 0.17312 \ \mathrm{M}\) So, the molar concentration of hydrobromic acid is approximately \(0.17312 \ \mathrm{M}\).

Key concepts

Net Ionic Equation

Understanding the net ionic equation is crucial when studying chemical reactions, particularly acid-base neutralization. It simplifies reactions to show only the species that actually participate in the reaction, which can help when predicting the outcomes of mixing different chemicals.

When two aqueous solutions react, some ions might not change during the reaction. These are called spectator ions and are not included in the net ionic equation. For instance, in the neutralization of hydrobromic acid by sodium hydroxide, the sodium ion is a spectator ion. The meaningful chemical change involves the hydrogen ion from the acid and the hydroxide ion from the base forming water, shown as
\( H^+ (aq) + OH^- (aq) \rightarrow H_2O (l) \).

This representation is powerful for focusing on the essence of chemical reactions without excess information. By using net ionic equations, predicting products and identifying reaction types can become more manageable for students.

Molar Concentration

Molar concentration, often referred to as molarity, is a measure of the concentration of a solute in a solution. It is defined as the number of moles of solute per liter of solution. The unit for molar concentration is moles per liter (M).

The formula to calculate molarity is
\( \text{Molarity} = \frac{\text{Moles of solute}}{\text{Volume of solution in liters}} \).

For the exercise involving hydrobromic acid and sodium hydroxide, the molarity is an essential concept in determining how much acid was needed to neutralize a given amount of base. Furthermore, understanding molarity is fundamental to performing dilutions and calculating reactant or product mass in stoichiometric calculations.

Stoichiometry

Stoichiometry is the quantitative relationship between reactants and products in a chemical reaction. It involves using the balanced chemical equation to determine the amount of products that form from a given quantity of reactants or vice versa.

In the context of the neutralization reaction between hydrobromic acid and sodium hydroxide, stoichiometry plays a vital role in determining the equivalence point where both the acid and base are present in stoichiometrically equivalent amounts.

Real-World Relevance

Mastery of stoichiometry is invaluable in fields ranging from pharmaceuticals to environmental science, as it ensures that chemical reactions are carried out with the precise amounts of each reactant to avoid waste and optimize yield.

Chemical Reactions

Chemical reactions involve the transformation of substances through the breaking and forming of chemical bonds, leading to new products. These reactions are classified into several types, including acid-base reactions, redox reactions, synthesis, decomposition, and precipitation.

Acid-base neutralization is a common chemical reaction where an acid reacts with a base to produce a salt and usually water. This type of reaction is pivotal in many industrial, biological, and environmental processes.

Practical Applications

In everyday life, neutralization reactions are used in antacid tablets to reduce stomach acidity or in environmental engineering to treat acidic waste before it's safely released into the environment. Understanding the various types of chemical reactions and their implications allows students to appreciate the scope and significance of chemistry in the world around them.