a) From inspection of your data in Table II, over what pH range does phosphate b

Question

a) From inspection of your data in Table II, over what pH range does phosphate buffer have its best

buffering capacity?How does your data support this?

b) Is your 0.10 M phosphate buffer or your diluted buffer better able to buffer against addition of acid

and base? How does your data support this?

d) From inspection of Tables II and III, which concentration of buffer gives measured pH values closest to

those you calculated? Is this what you would expect? Why or why not?

Thanks

Table II. Measured pH values for 0.10 M phosphate buffer, before and after addition of acid and base.. Measured pH Measured pH after addition of HCI Measured pH after addition of NaOH Calculated pH 6.0 5.42 5.33 6.02 6.5 5.96 3.84 6.20 7.0 6.61 6.40 6.68 7.5 7.10 6.69 7.20 8.0 7.66 6.92 10.44 Table III. Measured pH values for diluted phosphate buffer, before and after addition of acid and base.. Measured pH Measured pH after HCl added Measured pH after NaOH added Calculated pH 6.0 5.81 6.01 6.69 7.20 7.32 1.72 7.92 1.93 1.88 2.46 1.97 6.5 11.70 7.0 11.26 12.06 11.87 7.5 8.0

Explanation / Answer

a) A buffer is a solution of a weak acid and its conjugate base or a weak base and its conjugate base that keeps the pH of the solution constant; therefore, a buffer must be able to resist changes in pH of the solution upon addition of small amounts of a strong acid or base. It is clearly seen that the 0.1 M phosphate buffer is best able to withstand pH changes in the range 7.0-7.5 and hence, this is the range where the said buffer works best.

b) The diluted buffer shows abrupt changes in pH over all pH ranges and hence, the original 0.1 M phosphate buffer is best able to resist pH changes in the pH range 7.0-7.5.

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