Calcule el pH de las siguientes disoluciones (los valores de...

Calcule el pH de las siguientes disoluciones (los valores de $K_a$ y $K_b$ se encuentran en el Apéndice D): (a) ácido propiónico $\left(\mathrm{HC}_3 \mathrm{H}_5 \mathrm{O}_2\right) 0.095 \mathrm{M}$; (b) ion hidrogenocromato $\left(\mathrm{HCrO}_4^{-}\right) 0.100 \mathrm{M}$; (c) piridina $\left(\mathrm{C}_5 \mathrm{H}_5 \mathrm{~N}\right) 0.120 \mathrm{M}$.

Key Concepts

Dissociation Constants (Ka and Kb)

The dissociation constants, Ka for acids and Kb for bases, measure the strength of weak acids and bases respectively. These constants indicate the extent to which a compound dissociates in water, directly influencing the ion concentrations and thus the pH of the solution. They are key parameters in formulating the equilibrium expressions used to solve acid–base problems.

Weak Base Equilibrium

Weak base equilibrium refers to the partial association of a weak base with water to form its conjugate acid and hydroxide ions. The base dissociation constant (Kb) quantifies this process. Understanding the equilibrium behavior of weak bases is crucial for calculating their influence on the solution’s pH.

pH is a measure of the acidity or basicity of an aqueous solution, defined as the negative logarithm of the hydrogen ion concentration. It provides a scale to quantify how acidic or basic a solution is and is fundamental in acid-base chemistry.

Acid–Base Equilibrium

Acid–base equilibrium involves reversible reactions in which acids donate protons to bases in water. This equilibrium determines the concentrations of the various species present in solution, which in turn influence the overall pH. Understanding these equilibria is essential for predicting the behavior of different acidic and basic compounds in solution.

Weak Acid Equilibrium

Weak acid equilibrium describes the state in which a weak acid only partially dissociates into its ions in solution. The extent of this partial dissociation is quantified by the acid dissociation constant (Ka), and the equilibrium conditions allow for the estimation of the acid’s contribution to the hydrogen ion concentration, thereby affecting the pH.

Transcript

00:03 Problem 59.

00:06 Part a.

00:19 In part a, 0 .095m propionic acid is given.

00:29 So, initial concentration of propionic acid is 0 .095m.

00:44 And initial concentration of hydrogen ion and propionate ion is 0.

00:49 Now at equilibrium, according to, uh, at equilibrium, let's let xm of hydrogen ion is formed, therefore xm of propionate ion is also formed.

01:15 So, remaining concentration of propionic acid equilibrium is 0 .095 minus x.

01:27 Now, according to appendix d, we can write as ke equals to 1 .3 into 10 to the power minus 5 that is equals to concentration of product divided by concentration of reactants.

01:50 So, concentration of hydrogen ion into concentration of propionate ion divided by concentration of propionicaseed.

02:11 Now put the value, x squared, divided by.

02:17 0 .095 minus x now value of x is a very less as compared to 0 .095 because propionic acid is a weak acid and its dissociation alpha is very low therefore we can write as 1 .3 into 10 to the power minus 5 equals to x squared so we ignore this x so x squared divided by 0 .095.

03:04 Therefore, value of x equals to 1 .1 into 10 to the power minus 3, that is hydrogen ion concentration.

03:26 So, ph equals to minus log hydrogen ion concentration.

03:32 That is equal to minus log.

03:34 Log 1 .1 into 10 to the power minus 3 that is equals to 2 .95.

03:45 So this is value of ph for part a.

03:55 Now in part b, given that 0 .10m hydrogen chromat ion, it will dissociated into hydrogen chromation, it will dissociated into hydrogen and chromat ion.

04:14 At initially concentration of hydrogen and chromat ion at 0...

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