Buffer capacity=millimoles of NaOH (HCl) / 1L of buffer A. Preparation of the Bu

Question

Buffer capacity=millimoles of NaOH (HCl) / 1L of buffer
A. Preparation of the Buffer Molarity of Acetic Acid: Molarity of Sodium Acetate 0.l B. Proper Use of a pH Meter Initial pH of buffer solution C. Buffer Titration With a Strong Acid Molarity of HCl: Volume of HCI Volume of HCI pH Reading Added, mLs pH Read Added, mLs -0.60 0.00 4.b2 5.50 4.00 0.50 Lt. 55 000 3.15 1.00 50 D 3.34 4.45 1.50 1.00 3.75 2.00 4.3 3.00 1.50 5 0 4.29 8.50 2.50 4.24 1.00 3.13 2.90 9.60 10.00 12. Olo 2.00 4. Chemistry 132 EXPERIMENT 28

Explanation / Answer

2.a. Estimated volume of strong acid to reach buffer capacity is the volume of strong acid that can be added before the pH of the buffer changes significantly. From the tabular column C, it is observed that the pH value changes significantly only after adding more than 5.5 ml HCl (this is the answer). Just follow the differences in pH values on successive addition of 0.5 ml of the strong acid

2.b. Similarly, estimated volume of strong base to reach buffer capacity is 5.5 ml as observed in Table E. You can understand this by following the differences in pH values on successive addition of 0.5 ml of the strong base.

2.c. Calculated Buffer capacity for strong acid = Number of millimoles of strong acid added/(change in pH x volume of the buffer solution)

For this calculation, choose the region before reaching buffer capacity. We have just now estimated in 2.a. that the buffer pH does not vary signficantly untill the addition 5.5 ml HCl. So, we can consider the pH changes observed on adding 5 ml HCl to calculate the buffer capacity. Note that I have assumed the buffer volume to be 10 ml as it is not mentioned in your data sheet.

                                       Thus buffer capacity for strong acid = (5 ml x 0.101 M)/(4.62-4.06)x0.01L

                                                                                           = 90.2 millimoles acid/L buffer solution

2.d. From Table E, we can perform a similar calculation as in 2.c.

Buffer capacity for strong base = (5 ml x 0.0965 M)/(5.09-4.62)x0.01L = 102.6 millimoles base/L buffer solution

(I think the molarity of NaOH given above Table E must be 0.0965 M instead of 0.965 M. Please check)

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