Calculate the pH at the equivalence point in titrating 0.100 M solutions of each of the followin

step 1 So now we'll work on problem 48 from chapter 17. In this problem, we are asked to calculate the

Calculate the pH at the equivalence point in titrating 0.100...

Key Concepts

Acid-Base Titration

Acid-base titration is an analytical technique in which a solution of known concentration (the titrant) is gradually added to a solution of unknown concentration (the analyte) until the reaction between them is complete. This process relies on the precise reaction stoichiometry and is used to determine the concentration of the analyte by monitoring the pH change as the titrant is added.

Equivalence Point

The equivalence point in a titration is the point at which the quantity of titrant added exactly stoichiometrically reacts with the analyte. At this stage, the original acid or base has been completely neutralized. The pH at the equivalence point depends on the nature of the acid and base involved, with strong acid-strong base titrations typically giving a neutral pH, whereas titrations involving weak acids or weak bases result in a pH that is not equal to 7.

Conjugate Base Hydrolysis

In titrations involving weak acids, once the acid has been neutralized, its conjugate base remains in solution and can react with water in a process called hydrolysis. This reaction typically produces hydroxide ions, which causes the solution to become basic. The extent of hydrolysis, and hence the pH, is determined by the basicity of the conjugate base, which is related to the original acid’s strength.

Acid Dissociation Constant (Ka) and pKa

The acid dissociation constant (Ka) measures the strength of an acid in solution by quantifying the equilibrium established between the acid and its dissociation products. The pKa, which is the negative logarithm of Ka, is a more convenient and widely used expression of acid strength. These values are crucial for predicting the behavior of weak acids in titrations, particularly in determining the pH at the equivalence point.

Dilution Effects in Titration

During a titration, the volume of the solution increases as the titrant is added, leading to a dilution of the reactants and products formed. This change in volume affects the concentration of the ions in solution and must be considered when calculating the pH at the equivalence point, especially for titrations involving weak acids or bases where the ionization equilibrium is sensitive to concentration.

Transcript

00:01 So now we'll work on problem 48 from chapter 17.

00:10 In this problem, we are asked to calculate the ph at the equivalence point in titrating 0 .1 molar solutions of each of the following with 0 .08 molar and aoh.

00:23 So in the first part, part a, we're asked about titrating with hbr, hydrobromic acid.

00:33 Now for this one, we don't need to do any calculate.

00:35 Because we have a strong acid being titrated with a strong base, so the ph will equal 7 at the equivalence point.

00:55 So we'll move on to part b, where the acid, which we're titrating against, is chloros acid, h .cl .o .2, and the concentration is 0 .1 molar.

01:09 So here, we can go ahead and draw the equilibrium that will occur when the acid has been neutralized.

01:30 And so when the acid has been neutralized, the only thing that will be left is the conjugate base, clo2 minus, which will react with water, to give an equilibrium product of the acid again and oh h minus.

01:49 So if you know the concentration of clo2, which is necessary, because we need to know the initial concentration, we need to know this initial concentration here.

02:15 What we can do is we can multiply the concentrations by each other.

02:25 So you have 0 .1 times 0 .08, and this here will account for the volume.

02:35 So we add on the bottom where the total concentration will be equal to the sum of these two because that's what we were adding into the sample and this is equal to 0 .04 -molar.

02:59 So that's our initial concentration here...

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