2. 100mL of 0.40M solution bufferpH 7.0 3. 250mL of 0.040M a solution pH 7.0 wit
ID: 186228 • Letter: 2
Question
2. 100mL of 0.40M solution bufferpH 7.0 3. 250mL of 0.040M a solution pH 7.0 with 0.040M salt solution 4. a) 250ml of 0.040M Tris pH 7.0 b) What is the g of Tris and volume of 2M HCl required to change the pH? 2. 100mL of 0.40M solution bufferpH 7.0 3. 250mL of 0.040M a solution pH 7.0 with 0.040M salt solution 4. a) 250ml of 0.040M Tris pH 7.0 b) What is the g of Tris and volume of 2M HCl required to change the pH? 4. Add 10 mL of 0.1 M HCl to one liter of a 0.10 M sodium acetate buffer, pH 6.76 (pK, -4.76 for acetic acid). (2 pts)e a) Does the pH of the solution change? Calculate the pH of the buffer following the addition of HCI. b) How does this illustrate (or not) the general rule about choosing a buffer with a pk, within 1 pH unit of the desired pH?Explanation / Answer
a)
Yes the pH of the solution will change.
The new pH of the buffer solution can be calculated as follows:
0.01 l * 0.1M = 0.001moles HCl
1 l * 0.10 M = 0.1moles sodium acetate
Resulting pH = 4.76 + log 0.001/ (0.1-0.001)
= 4.76 + log (0.001 / 0.099) = (4.76 - 1.99) = 2.76
b) Let us suppose that the desired pH was 2.76. Then you had not chosen a pKa which is one pH below/above the desired pH. So, this example does not illustrate the general rule about choosing a buffer with a pKa within 1pH unit of desired pH.
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