CHEM 1C Chapter Notes - Chapter 18: Silver Nitrate, Sodium Hydroxide, Lewis Acids And Bases

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13 Oct 2017

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The acidity of the blood is important because ph has a narrow ph range it can function in. This nearly constant blood ph is maintained by buffers. Buffers resist ph changes by neutralizing added acid or base. When acid/base is added most solutions significantly change. However, buffers resist ph change by neutralizing added acid or added base. Significant amounts of both a weak acid and its conjugate base: 2. Significant amounts of both a weak base and its conjugate acid. Same thing with a weak base, it doesn"t have enough acid to be a buffer: a buffer must contain significant amounts of both weak acid and its conj. base (same with weak base) As long as the amount added of a base/acid is less than the amount of base/acid in the solution, the buffer will be able to neutralize it.

Related Questions

Need help with part B and C

Â± pH Changes in Buffers

When a solution contains a weak acid and its conjugate base or a weak base and its conjugate acid, it will be a buffer solution. Buffers resist change in pH following the addition of acid or base. A buffer solution prepared from a weak acid (HA) and its conjugate base (Aâ) is represented as

HA(aq)âH+(aq)+Aâ(aq)

The buffer will follow Le ChÃ¢telier's principle. If acid is added, the reaction shifts to consume the added H+, forming more HA. When base is added, the base will react with H+, reducing its concentration. The reaction then shifts to replace H+ through the dissociation of HA into H+ and Aâ. In both instances, [H+] tends to remain constant.

The pH of a buffer is calculated by using the Henderson-Hasselbalch equation:

pH=pKa+log[Aâ][HA]

Part A

What is the pH of a buffer prepared by adding 0.405 mol of the weak acid HA to 0.609 mol of NaAin 2.00 L of solution? The dissociation constant Ka of HA is 5.66Ã10â7.

Express the pH numerically to three decimal places.

Hints

pH =

6.424

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Correct

Since both the acid and base exist in the same volume, we can skip the concentration calculations and use the number of moles in the Henderson-Hasselbalch equation to calculate the pH. The answer will be the same.

Part B

What is the pH after 0.150 mol of HCl is added to the buffer from Part A? Assume no volume change on the addition of the acid.

Express the pH numerically to three decimal places.

Hints

pH =

6.165

All attempts used; correct answer displayed

Even though a significant amount of a strong acid was added, the pH of the buffer changed very little. If this amount of acid was added to 2.00 L of pure water, the pH would change from 7.000 to 1.125.

Part C

What is the pH after 0.195 mol of NaOH is added to the buffer from Part A? Assume no volume change on the addition of the base.

Express the pH numerically to three decimal places.

pH =

6.408

Incorrect; Try Again; 4 attempts remaining