1.)Complete the Henderson -Hasselbach equation: pH = ______ 2.)Fill in the blank
ID: 889999 • Letter: 1
Question
1.)Complete the Henderson -Hasselbach equation: pH = ______
2.)Fill in the blank: For polyprotic acids, by convention K1 refers to the acid species with the ______ protons.
3.)Fill in the blank: A buffer is a mixture of a weak acid and its______
4.)Fill in the blank: To make a buffer, we pick a weak acid with a pKa that is within ______ pH-units of the desired pH.
5.)Fill in the blank: That ____________ metal-ligand complexes are stronger than ____________ ones is called the chelate effect.
6.)If pH = 6, calculate: [H+] ________, pOH _________, [OH-] _________
7.)Fill in the blank: An acid-base indicator is itself a ________ _______, where the protonated form has a different ________ than the deprotonted form.
8.)Na+ has a Kf of 101.7 for binding to EDTA; Mn3+ has a Kf of 1025 for binding EDTA. Circle the metal that binds to EDTA more favorably.
9.)Based on the table of pKas below, circle the stronger acid.
Acid pKa
Propanoic acid 4.87
Cyano acetic acid 2.47
10.)An acid, HA, has a pKa1 of 5
a)What is the principal species, HA or A-, at pH = 4:
b)What is the principal species, HA or A-, at pH = 8:
c)What is the ratio of A- to HA at pH = 6:
d)At what pH would the ratio of A- to HA be one:
11.)The ion V3+ (10.00mL of 0.0100M metal ion buffered at pH 12) was titrated with 0.0100M EDTA. (useful tables are appended to this exam)
a)At this pH what percentage of all the EDTA in solution is in its most deprotonated form?
b)What is the equivalence volume in mL?
c)Calculate the conditional formation constant (Kf’) for Mn+.
d)Calculate the concentration of free metal ion (Mn+) at V = 10mL (i.e. after 10 mL of EDTA have been added).
e)Why is there usually a limit to how high the pH can be for an EDTA titration?
12.)For phosphoric acid (H3PO4):
pKa1 = 2.148, pKa2 = 7.199 and pKa3 = 12.15
a)What would be the pH of 0.1M NaH2PO4 in water?
(note that Na is a spectator ion; also this is NOT a titration problem)
b)What would be the pH of 0.1M Na3PO4?
(note that Na is a spectator ion; also this is NOT a titration problem) If you do not have a quadratic solver on your calculator you may use the “shortcut”, HOWEVER, you must evaluate your answer and state whether or not the shortcut is justified.
Problem continued from above:
For phosphoric acid (H3PO4):
pKa1 = 2.148, pKa2 = 7.199 and pKa3 = 12.15
c)Free-hand sketch a titration curve for 10.0mL of 0.010M H3PO4 with 0.010M NaOH. .
On the curve label the pH and volume for the following:
(1) the point where there are equal amounts of H3PO4 and H2PO4-
(2) the point where there is all H2PO4- in solution
(3) the point where there are equal amounts of H2PO4- and HPO42-
(4) the point where there is all HPO42- in solution
(5) the point where there are equal amounts of PO43- and HPO42-
13.)Multiple Choice: To make phosphoric acid buffer at pH 7…. (note your answers for 12, if correct, might help)
a)You would calculate the ratio of sodium Na2HPO4 to Na3PO4 you need, then combine the two species in that ratio.
b)You would take Na2HPO4and add NaOH until the pH reads 7.
c)You would calculate the ratio of H3PO4 to NaH2PO4 you need, then combine the two species in that ratio.
d)You would take NaH2PO4 and add NaOH until the pH reads 7.
14)For 50.0 mL of 0.020 M MES (pKa=6.15) titrated with 0.10M KOH, what is the pH after 3mL of KOH have been added?
15)What is the pH if we add 1.0mL of 1.00M HCl to a 100mL-solution that was initially at 0.1000M Tris and 0.0200M TrisH+ (pKa = 8.075)
16)See graph and questions below:
Reminder: SHOW ALL WORK
e)Multiple choice: What type of species is being titrated?
i)monprotic acid
iii) diprotic acid
iv)monoprotic base
v)triprotic acid
vi)triprotic base
vii)diprotic base
f)What is the approximate pKa2 of the species titrated (i.e. the analyte)?
g)What is the pKb2 of the species titrated (i.e. the analyte)?
h)Standard lab-type titration question: If each tick mark on the x-axis is 5.00mL, the concentration of the titrant is 1.00M and the initial volume of the analyte is 100.0mL, what is the initial concentration of the species titrated (i.e., the analyte) before any titrant was added?
i)Read off the plot the pH for:
i)fully protonated analyte: pH = _______
ii) fully deprotonated analyte: pH = ________
pleeeease help me, answer as much as possible.
Reminder: SHOW ALL WORK
Explanation / Answer
1) pH = pka + log[salt/acid] , pH = pkb + log[salt/base]
2) K1 gives information about dissociation of one proton that is first proton.
3) A buffer is a mixture of a weak acid and its salt with strong base.
4) +or- 1 pH-units of desired pH.
5) That chelating metal-ligand complexes are stronger than non chealating ones is called the chelate effect
6) pH = 6
pH = -log[H+]
[H+] = 10^-6 M
pOH = 14-6 = 8
[OH-] = 10^-pOH = 10^-8
7) acid or base ,pH
8) higher the Kf value more favorable the bond formation.
9) By decreasing Ka acidity increases.so that cyano aceticacid is more acidic.
10) a) the principal species are HA at pH = 4:
b) the principal species are A-, at pH = 8:
c) the ratio of A- to HA at pH = 6 is 10:1
d) pH= pka ,the ratio of A- to HA be one
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