Calculate the percent ionization of a 0.13 M formic acid solution in pure water and also in a so

Calculate the percent ionization of a 0.13 M formic acid...

Key Concepts

Common Ion Effect

When a salt containing the conjugate base of a weak acid is added to the solution, the common ion effect comes into play. The presence of the conjugate base decreases the acid's ionization by shifting the equilibrium position to favor the formation of the undissociated acid, as predicted by Le Chatelier's Principle.

Percent Ionization

Percent ionization refers to the fraction of the total acid that has dissociated into ions, expressed as a percentage. It is calculated by dividing the concentration of ionized acid by the initial concentration of the acid and multiplying by 100. This measure indicates the strength of the acid under given conditions.

Buffer Solutions

A buffer solution consists of a weak acid and its conjugate base, which work together to resist changes in pH when small amounts of acid or base are added. In this context, the introduction of potassium formate to a formic acid solution creates a buffer that stabilizes the pH and lowers the percent ionization of the acid.

Acid-Base Equilibrium

This concept describes how weak acids partially dissociate in water to form their conjugate bases and protons, establishing an equilibrium between the undissociated and ionized forms. It is crucial for calculating percent ionization, as the degree of dissociation depends on the acid’s strength and the conditions of the solution.

Acid Dissociation Constant (Ka)

Ka is a quantitative measure of the strength of a weak acid in solution. It reflects the extent to which the acid donates protons to water. In calculations involving percent ionization, using Ka helps determine the equilibrium concentrations of the ionized and undissociated acid.

Transcript

00:01 All right, so in this video we're going to be answering question 32 from chapter 17, which is calculate the percent ionization of a 0 .13 molar formic acid solution in pure water and also in a solution containing 0 .11 molar potassium formate.

00:18 Explain the difference.

00:19 So let's start calculating the percent ionization for the formic acid in pure water.

00:26 So percent ionization is just 100 percent percent ionization is just 100 percent times the ionized acid divided by the initial acid.

00:33 So we need to figure out how much of the acid is ionized before we can solve this.

00:38 So we're going to do an icebox problem.

00:41 So initially we have 0 .13 molar formic acid and nothing else.

00:46 We know that for every x -moles of formic acid that reacts, we form x moles of formate ions and hydronium ions.

00:55 So in our equilibrium row, we have 0 .13 minus x, x and x.

01:02 So we're going to plug these into our expression for the k a.

01:06 So our k a is just products divided by reactants formate times hydronium divided by formic acid and that's going to be equal to x squared divided by 0 .13 minus x and here this is just the k a tabulated value for formic acid.

01:22 So if we bring all of this to one side we have a quadratic equation equal to zero.

01:29 So we want to know the roots of this quadratic equation and you can do that with the quadratic formula you could graph it and find the zeros of it whatever way suits you best but we end up with x equals 0 .00475 molar so that's our concentration of formate and hydronium ions that we end up with and the percent ionization is just that divided by our initial concentration times 100 percent so we have three point 0 .7 % ionization for the formic acid in pure water...

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