Old Dominion UniversityCHEM 441PROBLEM SET 1 BIOCHEMISTRY. ( verified answers, 100% correct )
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PROBLEM SET 1 BIOCHEMISTRY
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Old Dominion University
Question 1 0.5 out of 0.5 points Which of the following statements is true about water? Select all answers that apply. Selected | C.liquid-phase water is more dense than solidphase water D . it is a weak acid E. it is a weak base Answers: A. it is non-polar B. it fully ionizes at neutral pH C. ...
old dominion universitychem 441problem set 1 biochemistry verified answers
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PROBLEM SET 1 BIOCHEMISTRY
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Question 1
0.5 out of 0.5 points
Which of the following statements is true about water? Select all answers that
apply.
Selected
C.
Answers:
liquid-phase water is more dense than solid-
phase water
D.
it is a weak acid
E.
it is a weak base
Answers: A.
it is non-polar
B.
it fully ionizes at neutral pH
C.
liquid-phase water is more dense than solid-
phase water
D.
it is a weak acid
E.
it is a weak base
Question 2
1 out of 1 points
-5 -
The Ka for a weak acid (HA) is known to be 1.9 x 10 . What is the ratio of [A ] to
[HA] at a pH of 6? Explain your answer & show all mathematical work.
Selected pH=pKa+log[A-]/[HA]
Answer: [A-]/[HA]=pH-pKa
[A-]/[HA]=10 pH x Ka= 10^+6 x 1.9 x 10^-5 = 19
[A-]/[HA]= 19
Correct Answer:
Since the Ka = 1.9 x 10-5, then the pKa = -log[1.9 x 10-5], which
is equal to 4.72.
Using the H/H equation:
pH = pKa + log([A-]/[HA])
6 = 4.72 + log([A-]/[HA])
1.28 = log([A-]/[HA])
So: [A-]/[HA] = 19.
Response [None Given]
Feedback:
Question 3
0.5 out of 0.5 points
,For questions 3-6, consider the titration curve below. The chemical species being
titrated by a strong base must be a __________ , since it is capable of donating
______ proton(s).
Selected E.
Answer:
triprotic acid;
three
Answers: A.
weak base; no
B.
strong base;
three
C.
monoprotic acid;
one
D.
diprotic acid; two
E.
, triprotic acid;
three
Question 4
0.5 out of 0.5 points
The chemical group being titrated around the point labeled (C) in the graph is
most likely a(n) ________________ (basic or acidic) group. [Blank1]
Specified Answer for: basi
Blank1
c
Correct Answers for: Blank1
Correct
Evaluation Method Case Sensitivity
Answer
Exact Match basic
Response Since the graph indicates the pKa is approximately 12.5 at point (C), then this
Feedback: must be a basic group, such as an amino group.
Question 5
0.5 out of 0.5 points
The titration curve shown in Question #3 is that of a free amino acid in aqueous
solution. Based on the graph, which particular amino acid is most likely
represented? Simply name the amino acid. [Blank1]
Specified Answer for: Arginin
Blank1
e
Correct Answers for: Blank1
Correct
Evaluation Method Case Sensitivity
Answer
Exact Match arginine
Response The titration curve clearly shows that the amino acid in question has three
Feedback: ionizable groups, due to the three distinct "steps" on the graph. So this means that
the amino acid must be Tyr, Cys, Lys, His, Arg, Asp, or Glu (these are the only free
amino acids with ionizable side chains). The chemical group at point (A) has a pKa
of a little over 2; the chemical group at point (B) has a pKa of approximately 9; the
chemical group at point (C) has a pKa of around 12.5. The only amino acid that fits
this pKa profile is ARGININE.
Question 6
1 out of 1 points
Assume that the equilibrium represented around point (A) in the titration can
generically be described as:
H3A + OH- ---> H2A- + HOH
What is the pH at which the ratio of [HA2-] to [H2A-] is 25:1? Show all work &
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