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Chapter 11: Problem 34

Benzoic acid is monobasic and when \(1.22 \mathrm{~g}\) of its pure sample after dissolution in distilled water is titrated against a base it uses \(50 \mathrm{~mL}\) of 0.2 \(\mathrm{M} \mathrm{NaOH}\). Calculate the molar mass of benz?ic acid.

Short Answer

Expert verified
The molar mass of benzoic acid is 122 g/mol.

Step by step solution

01

Write down the given information

We are given that the weight of benzoic acid is 1.22 g, the volume of the NaOH solution used in titration is 50 mL, and the concentration of NaOH is 0.2 M. We are asked to find the molar mass of benzoic acid.
02

Convert the volume of NaOH solution to Liters

Since the concentration is given in moles per liter (Molarity), we need to convert the volume from milliliters to liters. Conversion: \(50 \text{ mL} = 0.050 \text{ L}\).
03

Calculate moles of NaOH

Using the molarity formula \(Molarity (M) = \frac{Moles}{Volume (L)}\), calculate the moles of NaOH. Moles of NaOH = Molarity of NaOH * Volume of NaOH in liters = \(0.2 * 0.050 = 0.010 \text{ moles of NaOH}\).
04

Determine moles of benzoic acid used

Since benzoic acid is monobasic, it will react with NaOH in a 1:1 molar ratio. Therefore, the moles of benzoic acid will be equal to the moles of NaOH. Moles of benzoic acid = 0.010.
05

Calculate the molar mass of benzoic acid

Using the formula \(Molar Mass = \frac{mass}{moles}\), calculate the molar mass of benzoic acid. Molar Mass of benzoic acid = \(\frac{1.22 \text{ g}}{0.010 \text{ moles}} = 122 \text{ g/mol}\).

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Titration in Chemistry
Titration is a common laboratory technique used to determine the concentration of an unknown solution. In a typical titration, a measured volume of one solution (titrant) is gradually added to a known volume of another substance (analyte) until the reaction between the two is complete. The endpoint of the titration is often indicated by a color change with the help of an indicator, or by reaching a particular electrical measurement for redox titrations.

In the exercise provided, titration is used to find out how much base (NaOH) is needed to fully react with a known mass of benzoic acid. The point at which the reaction is complete is the equivalence point, where the number of moles of hydrogen ions in the acid equals the number of moles of hydroxide ions in the base. By knowing the volume and molarity of the NaOH base and the stoichiometry of the reaction, one can calculate the molar mass of benzoic acid.
Molarity Concentration
Molarity, denoted by 'M', is a unit of concentration used in chemistry to describe the number of moles of a solute divided by the volume of solution in liters. One mole of any substance contains Avogadro's number of entities (6.022 x 1023), whether they are molecules, atoms, or ions.

The formula for molarity is as follows:

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Most popular questions from this chapter

Cilculate the \(\mathrm{pH}\) of the resultant mixtures : (ii) \(10 \mathrm{ml}\). of \(0.2 \mathrm{M} \mathrm{Ca}(\mathrm{OH})_{2}+25 \mathrm{~mL}\) of \(0.1 \mathrm{MHCl}\), (b) \(10 \mathrm{ml}\). of \(0.01 \mathrm{M} \mathrm{H}_{2} \mathrm{SO}_{4}+10 \mathrm{~mL}\) of \(0.01 \mathrm{M} \mathrm{Ca}(\mathrm{OH})_{2}\), (c) \(10 \mathrm{ml}\) of \(0.1 \mathrm{MH}_{2} \mathrm{SO}_{4}+10 \mathrm{~mL}\) of \(0.1 \mathrm{M} \mathrm{KOH}\).

$$ \begin{aligned} &\text { A solution of } 0.01 M \text { concentration of } \mathrm{NH}_{4} \mathrm{OH} \text { is } 2.6 \% \text { dissociated. }\\\ &\text { Calculate }\left[\mathrm{H}^{+}\right],\left[\mathrm{OH}^{-}\right],\left[\mathrm{NH}_{4}^{+}\right],\left[\mathrm{NH}_{4} \mathrm{OH}\right] \text { and } \mathrm{pH} \text { of solution. } \end{aligned} $$

(a) Suggest a solvent in which aniline acts as strong base. (b) Write equation for the auto ionisation of (i) \(\mathrm{HCOOH}\), (ii) \(\mathrm{NH}_{3}\). (c) \(\left[\mathrm{Al}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{3+}\) is acid or base and write its conjugate partner and reaction. (d) Write the order of acidic nature of \(\mathrm{HCl}, \mathrm{HCOOH}\) and \(\mathrm{CH}_{3} \mathrm{COOH}\) in (i) \(\mathrm{H}_{2} \mathrm{O}\), (ii) liq. \(\mathrm{NH}_{3}\).

$$ \begin{aligned} &\text { How many mole of } \mathrm{N} \mathrm{H}_{4} \mathrm{Cl} \text { must be added to one litre of } 1.0 \mathrm{M} \mathrm{NH}_{4} \mathrm{OH}\\\ &\text { to have a buffer of } \mathrm{pH}=9 . K_{\mathrm{NH}_{4} \mathrm{OH}}=1.8 \times 10^{-5} ? \end{aligned} $$

The \(\mathrm{pH}\) of \(0.1 \mathrm{M}\) solution of cyanic acid (HCNO) is \(2.34\). Calculate the ionization constant of the acid and its degree of ionization in the solution.
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