Q1 - You need to produce a buffer solution that has a pH of 5.00. You already ha

Question

Q1- You need to produce a buffer solution that has a pH of 5.00. You already have a solution that contains 10. mmol (millimoles) of acetic acid. How many millimoles of acetate (the conjugate base of acetic acid) will you need to add to this solution? The pKa of acetic acid is 4.74. Express your answer numerically in millimoles.

Q2- Mg(OH)2 is a sparingly soluble salt with a solubility product constant, Ksp, of 5.61×1011. It is used to control the pH and provide nutrients in the biological (microbial) treatment of municipal wastewater streams. Calculate the ratio of solubility of Mg(OH)2 dissolved in pure H2O to Mg(OH)2 dissolved in a 0.200 mol L1 NaOH solution. Express your answer numerically to three significant figures.

Q2 "part B'' What is the pH change of a 0.240 mol L1 solution of citric acid (pKa=4.77) if citrate is added to a concentration of 0.175 mol L1 with no change in volume? Express the difference in pH numerically to two decimal places.

Explanation / Answer

Solution:- From Handerson equation.....

pH = pKa + log(base/acid)

5.00 = 4.74 + log(X/10.)

5.00 - 4.74 = log(X/10.)

0.26 = log(X/10.)

Taking antilog....

100.26 = X/10.

1.82 = X/10.

X = 1.82(10.)

X = 18.2

So, 18.2 mmol of acetate ion are required.

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