(a) Calculate the pH of a 0.050-M solution of benzoic acid, C6 H5 COOH ; Ka=1.2 ×10^-4 at 25^∘ C

(a) Calculate the pH of a 0.050-M solution of benzoic acid,...

Key Concepts

Percent Ionization

Percent ionization is a measure of the fraction of the original acid molecules that dissociate into ions in solution. It provides insight into how completely a weak acid ionizes and is useful for comparing the strength of different weak acids in solution.

Weak Acid Equilibrium

Weak acids do not ionize completely in solution. Instead, they establish an equilibrium between the protonated (acid) form and the deprotonated (conjugate base) form. This equilibrium behavior is essential for understanding how pH is affected in solutions of weak acids.

Acid Dissociation Constant (Ka)

Ka quantifies the extent of dissociation of a weak acid by comparing the concentrations of the ions produced at equilibrium. It is a fundamental measure that allows one to calculate the pH of the acid solution and understand the strength of the acid.

Equilibrium Expression and Approximations

The equilibrium expression relates the concentrations of the acid, its conjugate base, and hydrogen ions according to the dissociation process. In many cases, an approximation (such as assuming that the change in concentration is small relative to the initial concentration) is used to simplify the calculations and make it possible to calculate ion concentrations and pH.

pH Calculation

The pH of a solution is calculated from the hydrogen ion concentration, which in turn is determined from the acid dissociation equilibrium. Understanding pH helps in predicting the acidic or basic nature of the solution and is a key concept in acid-base chemistry.

Transcript

00:01 Question is calculate the ph of a 0 .05 molar solution of benzoic acid and ca is given and also calculate percentage of the acid that has ionized in the solution.

00:15 Okay.

00:17 So in the question we have initial concentration that is equal to 0 .05 and ka is equal to 1 .2 into 10 rate to the power minus.

00:31 Okay, and benzoic acid will be dissociate in the water like this.

00:42 Equilibrium will establish and c6h5 c .o .o.

00:48 Minus plus h3 plus.

00:53 First we have to calculate the concentration of acid, salt and hydrogen ion with the help of ice table.

01:02 So we will draw ice table.

01:05 Here will come acid and here will come salt and here will come hydrogen ion.

01:18 Correct.

01:19 At t equal to zero initially.

01:22 Initially acid is present and the concentration of this is 0 .05 molar.

01:29 Salt concentration is zero, hydrogen ion concentration 0.

01:33 Okay.

01:35 So what is the change? change is minus x x x because concentration of reactant is decreasing as the reaction forward goes and concentration at equilibrium at equilibrium that will be 0 .05 minus x x and x correct so what is the expression of ionization constant it will be k equal to ratio of concentration of salt and hydrogen ion to the concentration of react that is acid so in the question we have value of k a that is equal to 1 .2 into 10 ratio of power minus 4 x into x divide by 0 .05 minus x okay okay here, value of x is very, very less than, is very, very less than 0 .05 because benzoic acid is a very weak acid, so it will ionize very, very less...

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