POST-LAB QUESTION (7 points) In this lab, you prepared a buffer and then determi

Question

POST-LAB QUESTION (7 points) In this lab, you prepared a buffer and then determined its pH, but in a laboratory setting it is usually the other way around -you need a buffer at a particular pH, and this dictates its preparation. Describe how you would prepare 100 ml of 0.10 phosphate buffer at pH =6.5, given appropriate glass are, sodium phosphate, monobasic (NaHapo, pKa = 7.20) and sodium phosphate, dibasic (NaH PO. pKa = 12.35) at 25°C. Your answer should include calculations. (Note: The moles of each component must add to the buffer moles. Le. A + HA- 0.250 mol)

Explanation / Answer

To prepare 100 of 0.100 molar phosphate buffer pH =pKa+log(salt)/log(acid)

6.5=7.2+logsalt/acid

Let molarity of buffer = 0.1 molarity of salt Na2HPO4 = x and acid = 0.1-x

Log x/0.1-x = -0.7

X/0.1-x = anti -0.7

X/0.1-x =5.01

X= 0.125 mole per litre or 0.0125in 100 ml

0.0125mole acid and rest 0.09 salt in one 100 ml

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