Buffer
Solutions
Solutions
Which of the following solutions would make the best buffer system?
a. 0.10 M NaCl and 0.10 M HCl
b. 1.0 M CH3CH2COOH and 1.0 M NaCH3CH2COO
c. 0.10 M NaOH and 0.10 HCl
d. 1.0 M HNO3 and 1.0 NaNO3
e. 1.0 M HCN and 1.0 M NaCl
b. 1.0 M CH3CH2COOH and 1.0 M NaCH3CH2COO
What determines pH after the equivalence point of a weak base/strong acid titration?
The concentration of excess strong acid determines pH after the equivalence point.
What is the pH of a 2.0 L solution of 0.30 M HCN (Ka = 6.2 x 10-10) after addition of 722.0 mL 0.90 M NaOH?
pH = 12.26
What is the pH of a 0.1 M solution of acetic acid (Ka = 1.8 x 10-5)?
2.87
The second law of thermodynamics tells us…
a. the entropy of the universe is constant
b. entropy is neither created nor destroyed
c. the universe proceeds toward a state of lower entropy
d. the universe proceeds toward a state of higher entropy
e. the entropy of the universe may increase or decrease
d. the universe proceeds toward a state of higher entropy
What is the pKa for the acid HA if a solution of 0.65 M HA and 0.85 M NaA has a pH of 4.75?
pKa = 4.63
What is the pH for a strong acid/ strong base equivalence point in a titration?
pH at equivalence is neutral for strong acid/strong base or strong base/strong acid titration.
What is the pH when 20.0 mL of 0.20 M HCl is added to 60.0 mL of 0.133 M hydrazine (N2H4, Kb = 1.3 x 10-6)?
pH = 8.11
A 0.1 M solution of formic acid (HCOOH, Ka = 1.8 x 10^-4) has a pH of 2.50. What is the percent ionization of formic acid in solution?
3.16%
Which of the following is true?
a. the reverse of a spontaneous reaction is also spontaneous
b. a non-spontaneous process can be caused to occur
c. a highly spontaneous process always occurs rapidly
d. a spontaneous process moves a system out of equilibrium
b. a non-spontaneous process can be caused to occur
Which of the following solutions has the greatest buffering capacity?
a. 0.528 M CH3COOH and 0.197 M NaCH3COO
b. 0.365 M CH3COOH and 0.527 M NaCH3COO
c. 0.817 M CH3COOH and 0.862 M NaCH3COO
d. 0.124 M CH3COOH and 0.131 M NaCH3COO
c. 0.817 M CH3COOH and 0.862 M NaCH3COO
What is the pH at equivalence for a strong acid/ weak base titration?
pH <7
A solution is prepared by dissolving 0.36 mol of hydrofluoric acid and 0.36 mol of sodium fluoride
in water sufficient to yield 1.00 L of solution. Calculate the pH of this solution after the addition of
0.250 moles of solid LiOH. Assume no volume change upon the addition of base. The Ka for HF
is 3.5 × 10-4
4.20
A 0.05 M solution of ammonia (NH3, Kb = 1.8 x 10^-5) has a pH of 11.13. What is the percent ionization of ammonia in solution?
2.70%
Under which of the following conditions would one mole of argon (Ar) have the lowest entropy, S?
a. 14 ᵒC and 5 L
b. 87 ᵒC and 15 L
c. 87 ᵒC and 5 L
d. 14 ᵒC and 15 L
a. 14 ᵒC and 5 L
The pH of blood is 7.35. It is maintained in part by the buffer system composed of carbonic acid (H2CO3) and the bicarbonate (HCO3-) ion. What is the ratio of [bicarbonate]/[carbonic acid] at this pH? The Ka of carbonic acid is 4.2 x 10-7.
[A-]/[HA] = 9.40
What is the pH at equivalence for a weak acid and strong base titration
pH>7
A 50.0 mL sample of an aqueous H2CO3 solution is titrated with 0.345 M NaOH. The second equivalence point is reached with 83.5 mL of base. What was the initial concentration of the H2CO3?
[H2CO3]initial = 0.288 M
Explain the purpose of a buffer and how it works.
Weak acid/base conjugte pair, reduces changes in pH upon addition of titrant
CB and CA react with added strong acid or base to neutralize its addition
In which of the following pairs will the entropy of the first substance be greater than that of the second?
a. 1 mole of F2(g); 1 mole of Cl2(g)
b. 1 mole of I2(s); 1 mole of I2(g)
c. 1 mole of CaCO3(s); 1 mole of CaO(s) plus 1 mole of CO2(g)
d. 1 mole of H2(g) at 25ᵒ C; 1 mole of H2(g) at 50ᵒ C
e. 1 mole of O3(g); 1 mole of O2(g)
e. 1 mol of O3(g); 1 mol of O2(g)
Buffer solutions with the component concentrations shown below were prepared. Which of them should have the lowest pH?
a. [CH3COOH] = 0.25 M, [CH3COO-] = 0.25 M
b. [CH3COOH] = 0.75 M, [CH3COO-] = 0.75 M
c. [CH3COOH] = 0.75 M, [CH3COO-] = 0.25 M
d. [CH3COOH] = 0.25 M, [CH3COO-] = 0.75 M
e. [CH3COOH] = 1.00 M, [CH3COO-] = 1.00 M
c. [CH3COOH] = 0.75 M, [CH3COO-] = 0.25 M
At what point in a titration does pH = pKa, and why is this true?
pH = pKa at the half equivalence point, because half of the analyte has been converted to its conjugate form and the ratio inside the log of the Henderson-Hasselbalch equation reduces to 1, making the log equal to 0 (pH = pKa + log(1) --> pH = pKa).
An 80.0 mL sample of an aqueous H2SO4 solution is titrated with 0.650 M NaOH. The second equivalence point is reached with 91.4 mL of base. What was the initial concentration of the H2SO4
0.37M
Calculate the pH of a solution made by dissolving 0.10 moles of acetic acid (CH3COOH) and 0.10 moles of sodium hydroxide (NaOH) in enough water to make 1.00 liter of solution. (Ka for acetic acid is 1.8 x 10-5)
Can the entropy of a system ever decrease favorably?
No, it can decrease, but higher entropic states are favored, thus not favorably.