Calculate [OH^-] and pH in a solution in which the hydrogen sulfite ion, HSO3^-, is 0.429 M and

Calculate [OH^-] and pH in a solution in which the hydrogen...

Key Concepts

Henderson-Hasselbalch Equation

The Henderson-Hasselbalch equation is a useful tool for estimating the pH of a buffer solution. It relates the pH to the acid dissociation constant (pKa) and the logarithm of the ratio of the concentrations of the conjugate base to the weak acid. This equation simplifies the assessment of pH when both components of the buffer are known, making it invaluable in both laboratory and theoretical settings.

Relationship Between pH, pOH, and Hydroxide Ion Concentration

This principle explains how pH and pOH are interrelated through the ion product of water, where pH + pOH = 14 at standard conditions. The concentration of hydroxide ions ([OH?]) is directly related to the pOH value, with lower [OH?] corresponding to higher pOH and vice versa. Mastering this concept is essential for converting between different measures of acidity and basicity in aqueous solutions.

Acid-Base Equilibrium

This concept pertains to the dynamic balance between acids and bases in solution, where a weak acid partially dissociates into its conjugate base and a proton. Understanding acid?base equilibrium involves writing the equilibrium expression for the dissociation, which relates the concentrations of the species involved through the acid dissociation constant (Ka). This lays the groundwork for calculating pH and understanding the behavior of buffer systems.

Buffer Systems

A buffer system is a solution that resists significant changes in pH upon the addition of small amounts of acid or base. It typically consists of a weak acid and its conjugate base (or a weak base and its conjugate acid). In buffer solutions, the ratio of the concentrations of the conjugate pairs determines the pH, providing a protective mechanism against pH fluctuations and ensuring stability in various chemical and biological environments.

Transcript

00:01 Okay, so we're going to find the ph and the hydroxide ion concentration of several buffer solutions here.

00:07 We know that through all these buffers, the hso3 minus concentration is going to stay at 0 .429 molar.

00:14 And the easiest way to find the concentrations of h plus and oh minus for buffers is to use this equation.

00:22 Here, h plus is ka concentration of the acid over the base.

00:26 So we'll go ahead for this first example.

00:29 Okay, we'll plug in our ca, which is 6 .0 times 10 to the negative 8.

00:36 The concentration of our acid is going to be 0 .429 the entire time.

00:43 And for this first one, the concentration of our base is 0 .0249.

00:49 So we'll multiply that out, and we'll get 1 .03 times 10 of the negative 6 molar h plus.

00:58 So if we go ahead and take the negative the log of that, so ph negative log of 1 .06 times 10 to minus 6, we'll give us a ph of 5 .99.

01:10 And also we can find the oh minus, right? oh minus is simply kw over h plus.

01:18 So 1 times 10 to negative 14 divided by 1 .03 times 10 of the negative 6.

01:23 We'll give us our oh minus.

01:25 So 9 .7 times 10 of the negative 9 molar, oh h minus so these next are going to be the same the only thing that's changing in these examples in this problem is going to be the value of the concentration of the base so k a is the same the weak acid is still 0 .429 molar and the base in this second example is 0 .247 so we multiply that we'll get our 1 .04 times 10 of the negative 7.

02:07 That's the molarity of the h plus.

02:10 If we take negative the log of that, we'll get our ph, and our ph will come out to be 6 .98.

02:18 And again, hydroxide ion is just going to be 1 times 10 to minus 14 divided by h plus.

02:25 So you'll get 9 .6 times 10 of the negative 8 molar oh, h minus.

02:36 More, again, where not much is changing.

02:40 So once you get the hang on one of these, you've probably got them all.

02:46 0 .429 molar of our acid.

02:51 And in this example, our base is 0 .504 molar...