Question 1

What would be the molar ratio of cyanic acid (HCNO)/sodium cyanate (NaCNO) buffer having a pH of 4.80? [Ka(HCNO) = 2.0 * 10-4]

Accepted Answer

A)  10.6 mol NaCNO to 1.0 mol HCNO 
B)  11.6 mol NaCNO to 1.0 mol HCNO 
C)  12.6 mol NaCNO to 1.0 mol HCNO 
D)  13.6 mol NaCNO to 1.0 mol HCNO 
E)  None of the above 
A)  10.6 mol NaCNO to 1.0 mol HCNO 
B)  11.6 mol NaCNO to 1.0 mol HCNO 
C)  12.6 mol NaCNO to 1.0 mol HCNO 
D)  13.6 mol NaCNO to 1.0 mol HCNO 
E)  None of the above

Question 2

Starting with 0.750L of a buffer solution containing 0.30 M benzoic acid (C6H5COOH) and 0.35 M sodium benzoate (C6H5COONa), what will the pH of the solution be after the addition of 340.0 mL of 0.350M HCl (Ka (C6H5COOH) = 6.5 x 10-5)

Accepted Answer

A)  4.19 
B)  4.25 
C)  3.81 
D)  0.45 
E)  6.54 
A)  4.19 
B)  4.25 
C)  3.81 
D)  0.45 
E)  6.54

Question 3

Calculate the pH at the equivalence point for the titration of 0.25 M CH3COOH with 0.25 M NaOH. (For CH3COOH, Ka= 1.8 *10-5.)

Accepted Answer

A)  8.92 
B)  8.72 
C)  8.52 
D)  8.32 
E)  None of the above 
A)  8.92 
B)  8.72 
C)  8.52 
D)  8.32 
E)  None of the above

Question 4

Find the concentration of calcium ions in a solution made by adding 3.50 g of calcium fluoride to 750. mL of 0.125 M NaF. [For CaF2, Ksp = 3.95 * 10-11.]

Accepted Answer

A)  3.16 * 10-10 M 
B)  2.53 * 10-9 M 
C)  4.29 * 10-4 M 
D)  6.32 * 10-10 M 
E)  2.15 * 10-4 M 
A)  3.16 * 10-10 M 
B)  2.53 * 10-9 M 
C)  4.29 * 10-4 M 
D)  6.32 * 10-10 M 
E)  2.15 * 10-4 M

Question 5

What mass of sodium fluoride must be added to 250. mL of a 0.100 M HF solution to give a buffer solution having a pH of 3.50 [Ka(HF) = 7.1* 10-4]

Accepted Answer

A)  0.49 g 
B)  1.5 g 
C)  3.4 g 
D)  2.3 g 
E)  0.75 g 
A)  0.49 g 
B)  1.5 g 
C)  3.4 g 
D)  2.3 g 
E)  0.75 g

What would be the molar ratio of cyanic acid (HCNO)/sodium cyanate (NaCNO) buffer having a pH of 4.80? [K_a(HCNO) = 2.0 * 10^-4]

Starting with 0.750L of a buffer solution containing 0.30 M benzoic acid (C₆H₅COOH) and 0.35 M sodium benzoate (C₆H₅COONa), what will the pH of the solution be after the addition of 340.0 mL of 0.350M HCl (K_a (C₆H₅COOH) = 6.5 x 10^-5)

Calculate the pH at the equivalence point for the titration of 0.25 M CH₃COOH with 0.25 M NaOH. (For CH₃COOH, K_a= 1.8 *10^-5.)

Find the concentration of calcium ions in a solution made by adding 3.50 g of calcium fluoride to 750. mL of 0.125 M NaF. [For CaF₂, K_sp = 3.95 * 10^-11.]

What mass of sodium fluoride must be added to 250. mL of a 0.100 M HF solution to give a buffer solution having a pH of 3.50 [K_a(HF) = 7.1* 10^-4]

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