What is the effective pH range of a buffer? For this experiment, you will be cre

Question

What is the effective pH range of a buffer? For this experiment, you will be creating an acetate buffer, which is acidic. Look up the pKa of acetic acid, and be sure to cite where this information was obtained. Based on the pKa of acetic acid, what is the effective pH range of a buffer made with acetic acid? The blood buffer system is one example of a buffer that is present naturally in the body. Look up two additional buffer systems present in the body, and why they are important. Be sure to cite where this information is obtained. Use the following steps to determine how to make 600 mL of a 0.1 M acetate buffer, pH 5.0, using 0.1M acetic acid and 0.1M sodium acetate. Using the desired pH (5.0) and pKa of acetic acid, use the Henderson-Hasselbalch equation to determine a ratio of [base]/[base] required for this buffer. Your answer should look something like this: [base]/[acid] = 2.3 Given the example above, we can set [acid] = x and [base] = 2.3x. Remember that the concentration of acid and base should equal the desired molarity, which 0.1. Based on this, a second equation can be obtained - given the example above, the equation would be x + 2.3x = 0.1. Use this to solve for x, which represent the concentration of acid ([acid]), and also for [base]. C. Use M_1V_1 = M_2V_2 to solve for the volume of 0.1 M acetic acid and 0.1M sodium acetate required to create the buffer. i. M_1 = 0.1M of acetic acid or 0.1M sodium acetate (stock solution) ii. V_1 = What to solve for iii. M_2=the value for [acid] or [base] solved in 4b iv. v_2 = the desired buffer volume (600mL)

Explanation / Answer

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1. The pH of a buffer is given by Henderson equation:

pH = pKa + log [base]/ [acid]

The pKa value of the weak acid is used in this formula. A buffer is effective only when the pH of the solution is close to its pKa.

So the effective pH range of a buffer is +1 or -1 of the pKa value

2. The pKa of acetic acid is 4.76.

This is taken from the acetic acid page of wikipedia.

So when a buffer is made from acetic acid, the effective pH range is +1 or -1 of 4.76

4.76 + 1= 5.76

4.76 - 1 = 3.76

So the effective pH range of an acetic acid buffer is 3.76 to 5.76

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