Nyb Fall 07 Unit Test 3

NAME: 202-NYB-05 Fall 2007 Section 31 Class Test 3 Green 1. a)You are required to make 250.0 mL of a buffer of pH = 4.80. Choose the components from the list below and calculate the volume of each required. (10 MARKS) i) 0.100 M acetic acid (Ka = 1.8 x 10-5) ii)0.075 M potassium phosphate

iii) 0.144 M barium acetate iv) 0.100 potassium hydrogen phosphate (Ka = 6.3 x 10-8)

b) What will the resulting pH be when 15.0 mL of 0.100 KOH (aq) are added. (10 MARKS)

2. 40.00 mL of an unknown monoprotic weak acid solution are titrated with 0.226 M sodium hydroxide. The equivalence point is reached after 25.00 mL of base have been added. a) What is the concentration of the acid solution? (5 MARKS)

b) The pH of the solution at the equivalence point is 8.24. Which of the following acids is in the solution? (10 MARKS) i. Hydrocyanic acid, Ka = 6.2 x 10-10 ii. Chloroacetic acid, Ka = 1.4 x 10-3 iii. Formic acid, Ka = 1.8 x 10-4

3. Below is a plot of the titration 25.00 mL of citric acid with 0.200 M sodium hydroxide. 14.0 12.0 10.0

p[H]

8.0 6.0 4.0 2.0 0.0 0.0

10.0

20.0

30.0

40.0 50.0 Volume of titrant (mL)

60.0

70.0

80.0

90.0

a) Calculate the concentration of the citric acid solution. (5 MARKS)

b) What is the pKa of citric acid? (2 MARKS)

c) On the graph above, sketch the titration of a weak base with a strong acid. (3 MARKS)

4. Explain why marble statues are adversely affected by acid rain. (5 MARKS)

5. Determine if the following salts will be acidic, basic or neutral in solution. (5 MARKS) a) Chromium(III) chloride________________ b) Lithium acetate__________________ c) Ammonium iodide ______________ d) Magnesium bromide _______________ e) Manganese(IV) bromide ____________

6. A microbiologist prepares a phosphate buffer from 0.60 M KH2PO4 and 0.60 M K2HPO4. At 25 oC, the pH of the buffer is 8.23. At 37 oC the pH of the buffer is 7.83. Explain. Calculate the Ka at 37 oC. Is the equilibrium endo- or exothermic? (KH2PO4 Ka (25 oC) = 6.3 x 10-8) (10 MARKS)

BONUS (2 MARKS) A Haiku is a poem that has three lines. The first line has five syllables, the second line had seven and the third has five. Write a haiku about any subject we have discussed in class.