Pre-Lab Questions: Answer the following questions in your laboratory notebook be

Question

Pre-Lab Questions: Answer the following questions in your laboratory notebook before coming to class. Be sure to cite any outside sources used to answer questions if necessary 1. What is the effective pH range of a buffer? 2. 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? 3. 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 4. Use the following steps to determine how to make 600 mL of a 0.1M acetate buffer, pH 5.0 using 0.1M acetic acid and 0.1M sodium acetate a. Using the desired pH (5.0) and pKa of acetic acid, use the Henderson-Hasselbalch [base] equation to determine a ratio of required for this buffer acid] [base] 2.3 [acid] (Note that this is NOT the ratio you will obtain it is just an example) b. Given the example above, we can set [acid] -xand Ibase] 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 represents the concentration of acid a CI and also for [base] Use 1 1 M2V2 to solve for the volume of 0.1M acetic acid and 0.1M sodium acetate required to create the buffer M1 0.1M of acetic acid or 0.1M sodium acetate (stock solution) i. V1 what to solve for ii. M2 the value for Lacid] or [basel solved in 4b iv. V the desired buffer volume (600mL)

Explanation / Answer

1. pH range of buffer may be for acidic buffer is pKa+1 to pKa-1.

2. pKa of acidic buffer = 4.75

pH range of buffer is 3.75 to 5.75

3. Blood buffer(bicarbonate buffer) , plasma protein buffer , phosphate buffer.

4. pH = pKa + log [salt/acid]

5.0 = 4.75 + log [salt/acid]

[salt/acid] = 1.78

[base/acid] = [salt/acid] = 1.78

from the data salt = 1.78x , acid = x

x+1.78x = 0.1

x =0.1/2.78 = 0.036 = acid ,

salt = 1.78*0.036 = 0.064

volume of salt (V2) = M1V1/M2 = 0.064*600/0.1= 384 ml

Volume of acid = 0.036*600/0.1 = 216 ml

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