Question

A 0.2688 -g sample of a monoprotic acid neutralizes \(16.4 \mathrm{~mL}\) of \(0.08133 \mathrm{M}\) KOH solution. Calculate the molar mass of the acid.

Short answer

The molar mass of this monoprotic acid is approximately \(200.6 \, \, g/mol\).

Step-by-step solution

Calculate moles of KOH

The moles of KOH can be calculated by multiplying its volume in liters (by converting ml to liters we get \(16.4 \,\, ml=0.0164 \,\, l\)) by its molarity which is \(0.08133 \, \, M\). Thus, \(0.0164 \, \, l\times 0.08133 \, \, M=0.00134 \, \, mol\).

Determine the moles of the monoprotic acid

As our acid is monoprotic, it means that one mole of the acid reacts with one mole of KOH. Hence, the moles of the monoprotic acid can be assumed to be equal to the moles of KOH i.e., \(0.00134 \, \, mol\).

Calculate the molar mass

Molar mass is calculated by dividing the mass of the substance by the number of moles. Since we have 0.2688 g of the acid and it is 0.00134 mol, its molar mass would be \(\frac{0.2688 \, \, g}{0.00134 \, \, mol}= 200.6 \, \, g/mol\).

Key concepts

Monoprotic Acid

A monoprotic acid is an acid that can donate only one proton or hydrogen ion (H⁺) per molecule in a chemical reaction. This characteristic makes naming and understanding these acids easier. Examples include hydrochloric acid (HCl) and nitric acid (HNO₃).
In the context of the given exercise, a monoprotic acid reacts with potassium hydroxide (KOH) in a one-to-one ratio. This means that each mole of the acid will completely neutralize one mole of KOH. This is important for determining the number of moles used in the titration, making calculations straightforward and facilitating our understanding of the concept of molar mass.

Neutralization Reaction

A neutralization reaction happens when an acid reacts with a base to form water and a salt. This type of reaction is fundamental in chemistry, especially in titration experiments where measuring the point of neutralization allows for the calculation of unknown concentrations.
In our case, the monoprotic acid reacts with KOH during the neutralization process. Given the monoprotic nature of the acid, the reaction proceeds with a 1:1 stoichiometric ratio to form water and the respective salt. Such reactions typically involve quantitative measurements that help in calculating parameters like molar mass, which is essential for understanding the mass and concentration of various compounds.

Moles Calculation

Calculating moles is a crucial step in many chemical analyses, including titration problems. The formula for calculating moles is based on the relationship: \[ \text{moles} = \text{Molarity} \times \text{Volume in liters} \]In the given exercise, this calculation involves finding the number of moles of KOH used during the titration. By converting the given volume from milliliters to liters, we apply the formula to find that 0.0164 liters of 0.08133 M KOH solution provides 0.00134 moles of KOH. This value directly indicates the moles of monoprotic acid, given that they react in a 1:1 ratio. Understanding this relationship is crucial for further calculations, such as determining the molar mass.

Acid-Base Titration

Acid-base titration is a precise analytical method used to determine the concentration of an acid or base in a solution. During titration, a solution of known concentration (the titrant) is gradually added to a solution of the analyte until the reaction reaches its endpoint, indicated by a sudden change in a property such as pH.
In this exercise, the titrant is KOH, and the analyte is the monoprotic acid. By meticulously measuring the amount of KOH needed to neutralize the acid, one can calculate the molar mass of the acid. This detailed analysis not only helps to identify the unknown acid but also enriches the understanding of chemical reactions and the properties of acids and bases. Proper technique and precise measurements are essential for accurate results in titration experiments.