CH 223

LECTURE # 15

SAMPLE QUESTIONS

• The lesson is for not only accuracy, but speed.

• You will always be under some time constraint.

• You can work in pairs or singly, whatever you are comfortable with.

• You will have approximately 7 minutes for each question, and 2 minutes to view the solution. These are standard exam-type questions.

ONE

The Ksp for Ag2CrO4 is 1.12x10-12

and that of AgCl is 1.77x10-10.

• Calculate the solubility of each.

• Which is more soluble in water?

TWO

A solution is made up by combining

22.5 mL of 0.25 M acetic acid and

1.82 g of sodium acetate dissolved in

17.5 mL.

What is the pH of this solution?

(use your periodic table to find the molar mass of sodium acetate).

Follow up To Question TWO

If one adds 5.0 mL of 0.05 M NaOH to

the buffer made above, what would

Be the final pH?

THREE

Both Ba2+ and Ca2+ ions form precipitates with SO4

2-. Ksp values are 1.07x10-10 for the barium salt, and 7.10x10-5 for calcium.

Which will precipitate first in a solution which contains 4.22x10-4 M Ba2+ and 3.27x10-3 M Ca2+ ?

Follow up To Question THREE

Calculate concentrations of Ca2+ and Ba2+ when Ca2+ starts to precipitate and when Ba2+ starts to precipitate.

FOUR

A 0.5224 g sample of an unknown monoprotic acid was titrated with 0.0998 M NaOH. The equivalence point of the titration occurs at 23.82 mL. Determine molar mass of the unknown acid.

FIVE

A 25.0 mL aliquot of a 0.100 M HCN (Ka=4.9x10-10) is titrated against a 0.100 M NaOH solution. Calculate the pH at the equivalence point. What would be a suitable indicator for this titration?

SIX

A 5.55 g of a weak acid, Ka=1.3x10-4 was combined with 5.00 mL of a 6.00 M NaOH solution and diluted to 750 mL. The final pH of this solution is 4.25. Calculate molar mass of the weak acid.