A buffer is made up of 355 mL each of 0.200 M NaHCO3 and 0.134 M Na2 CO3. Assuming that volumes

A buffer is made up of 355 mL each of 0.200 M NaHCO3 and...

A buffer is made up of $355 \mathrm{~mL}$ each of $0.200 \mathrm{M} \mathrm{NaHCO}_{3}$ and $0.134 \mathrm{M}$ $\mathrm{Na}_{2} \mathrm{CO}_{3}$. Assuming that volumes are additive, calculate (a) the $\mathrm{pH}$ of the buffer. (b) the $\mathrm{pH}$ of the buffer after the addition of $0.0300 \mathrm{~mol}$ of $\mathrm{HCl}$ to $0.710 \mathrm{~L}$ of buffer. (c) the $\mathrm{pH}$ of the buffer after the addition of $0.0300 \mathrm{~mol}$ of $\mathrm{KOH}$ to $0.710 \mathrm{~L}$ of buffer.

A buffer is made up of $355 \mathrm{~mL}$ each of $0.200 \mathrm{M} \mathrm{NaHCO}_{3}$ and $0.134 \mathrm{M}$ $\mathrm{Na}_{2} \mathrm{CO}_{3}$. Assuming that volumes are additive, calculate
(a) the $\mathrm{pH}$ of the buffer.
(b) the $\mathrm{pH}$ of the buffer after the addition of $0.0300 \mathrm{~mol}$ of $\mathrm{HCl}$ to $0.710 \mathrm{~L}$ of buffer.
(c) the $\mathrm{pH}$ of the buffer after the addition of $0.0300 \mathrm{~mol}$ of $\mathrm{KOH}$ to $0.710 \mathrm{~L}$ of buffer.

Key Concepts

Acid-Base Reaction Stoichiometry

Stoichiometry in acid-base reactions deals with the quantitative relationships between acids and bases during neutralization reactions. In the context of buffers, it is used to calculate how the concentrations of the weak acid and its conjugate base change when a known amount of strong acid or base is added, thereby allowing for the subsequent determination of pH shifts.

Buffer Solutions

A buffer solution is composed of a weak acid and its conjugate base or a weak base and its conjugate acid. It is designed to resist pH changes when small amounts of a strong acid or base are added. This resistance is due to the equilibrium between the weak acid and its conjugate base, which allows the system to neutralize added H+ or OH– ions.

Henderson-Hasselbalch Equation

The Henderson-Hasselbalch equation is a formula that relates the pH of a buffer solution to the pKa of the weak acid and the ratio of the concentrations of its conjugate base to the acid. It simplifies the calculation of pH in buffer systems by providing a direct link between these quantities, making it a critical tool in understanding and designing buffer solutions.

Buffer Capacity

Buffer capacity refers to the ability of a buffer solution to maintain its pH despite the addition of acids or bases. It is determined by the absolute amounts of the buffering components rather than just their ratio, indicating how much strong acid or base can be neutralized before a significant pH change occurs.

Transcript

00:01 Okay, so let's start by figuring out how many moles of each substance we have here.

00:06 Okay, so we have 0 .2 molar and 0 .355 liters.

00:12 So that's going to give us 0 .0710 moles of the weak acid, which is bicarbonate, and 0 .134 molar in the same volume, which will give us 0 .04 -molar, and the same volume, of its conjugate base carbonate.

00:37 Okay, so we have a weak acid in its conjugate base, so that is going to be a buffer.

00:44 So our relationship for buffers is h plus is k -a times the moles of acid divided by the moles of base.

00:57 So that'll be 4 .7 times 10 and negative 11.

01:03 So moles of acid over moles of base.

01:10 So this will give us 7 .0 .0.

01:12 Times 10 to negative 11 molar.

01:15 That's our h plus concentration.

01:18 So if i take minus the log of that, we'll get the ph, and that will be 10 .15.

01:26 In the second example, we're adding some strong acid.

01:30 That strong acid is going to react with the weak base part of the buffer to make some more weak acid.

01:39 So let's just do a little table where we keep track of the stoichiometry, initial change and final.

01:44 So 0 .03 is what we're adding to 0 .0476.

01:53 And don't forget you have 0 .071 of this to start.

01:58 The h -plus is our limiting reactant.

02:02 So we'll go ahead and subtract and add 0 .03.

02:09 So we'll give a 0 .1 of that .0 .176 moles and 0 .101 .1 .1 .1 .1 moles.

02:18 So we have a weak base and its conjugate weak acid.

02:25 So that's a buffer...

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