CHM1212K PRELAB Quiz Last Name: First Name: Date Pre-Lab Questions for Lab 11: B
ID: 1043855 • Letter: C
Question
CHM1212K PRELAB Quiz Last Name: First Name: Date Pre-Lab Questions for Lab 11: Buffer Solutions 1. (40 Points) Define: A. (20 Points) Buffer Solution B. (10 Points) Buffer capacity C. (10 Points) Buffer range 2. (20 points) What is the pH of a solution prepared by mixing 25.00 mL of 0.10 M CH3CO.H with 25.00 mL of 0.050 M CHyCONa? Assume that the volume of the solutions are additive and that Ka 1.8 x 10-5 for CH3CO2H? 3. (20 Points) You wish to prepare an HC2H302 buffer with a pH of 4.24. If the pKa of is 4.74, what ratio of C2H302 /HC2H302 must you use? 4. (10 Points) Which is the best acid to use in the preparation of a buffer with pH3.3 (Explain) A) HOI (Ka 2.0 x 10-11) B) HNO2 (K 4.5 10-4) C) HNO3 D) HIO3 ((K 1.7 10-1) 5. (10 Points) Which statement about buffers is true? A) Buffers have a pH 7 B) Buffers consist of a strong acid and its conjugate base. C) A buffer does not change pH on addition of a strong acid or strong base. D) Buffers resist change in pH upon addition of small amounts of strong acid or strong base.Explanation / Answer
1.
A.
Buffer Solution : A solution which resists to change in its pH by the addition of small amount of strong acid or strong base.
B.
Buffer Capacity : A measure of reesistance of a buffer to change its pH on addition of hydroxide ions.
C.
Buffer range : The range of pH at which buffer is effective.
2.
pH = pKa + Log[Salt]/[Acid]
pH = - Log(1.8 * 10-5) + Log[(0.050 * 25.00) / ( 0.10 * 25.00)]
pH = 4.44
3.
4.24 = 4.74 +Log[Salt]/[Acid]
Log[Salt]/[Acid] = - 0.5
[Salt] / [Acid] = 0.316
4.
(B) HNO2 is best at pH 3.3
Because,
pKa = - Log(4.5 * 10-4) = 3.35
5.
(D)