AP Chemistry Practice Exam 2 ❮ 34512. The chemical equation for the reaction described
in the table indicates that there are three reactants
(H+, H 2 O, and CN 2 H 4 O); however, only two
reactants appear in the data table. Why is there
no column in the table for the third reactant?
(A) The H 2 O behaves as a catalyst.
(B) The H 2 O is not a reactant; it is the solvent.
(C) The H 2 O concentration does not change.
(D) It is only possible to deal with two reactants.- Oxalic acid, H 2 C 2 O 4 , is a useful chemical for
rust removal. A student prepared five oxalic acid
samples by dissolving 0.9000 grams of oxalic acid
in 100.00 mL of water and pipetting 10.00 mL
samples of this solution into five separate beakers.
Each of the samples was diluted with deionized
water, and an appropriate indicator was added as
an indicator. The samples were then titrated with
standard 0.05000 M sodium hydroxide, NaOH,
until the appearance of a permanent color change
of the indicator indicated the endpoint of the
titration. The following volumes were obtained.
Molar mass of H 2 C 2 O 4 = 90.04 g mol-^1.
VOLUME OF
STANDARD NaOH
Sample 1 39.68 mL
Sample 2 40.27 mL
Sample 3 40.54 mL
Sample 4 39.66 mL
Sample 5 39.74 mLThe student calculated a concentration of
approximately 0.20 M in each case. This is not
the correct value. What is the most likely mistake
that the student made?
(A) The student used the total sample volume
of the acid instead of the pipetted sample
volume.
(B) The student did not use the correct mole
ratio in the calculation.
(C) The student did not use the correct indicator.
(D) The student contaminated the samples
during preparation.- Co^2 + + 2 e- → Co E ° = −0.28 V
Zn^2 + + 2 e- → Zn E ° = −0.76 V
Given the above standard reduction potentials,
estimate the approximate value of the ΔG ° for
the following reaction:
Zn + Co^2 + → Zn^2 + + Co
(A) -4.6 × 104 J mol-^1
(B) -9.3 × 104 J mol-^1
(C) +9.3 × 104 J mol-^1
(D) +4.6 × 104 J mol-^1Use the following information to answer questions
15–19.
pH versus volume of titrant added0G HF
pHVolume strong acid addedEThe diagram above represents the idealized titra-
tion curve for the reaction of pure sodium
carbonate, Na 2 CO 3 , with a strong acid such as
hydrochloric acid, HCl. E and F represent the
pH at the endpoints corresponding to the forma-
tion of HCO 3 - and H 2 CO 3 , respectively. G and
H correspond to the quantity of acid required to
reach the endpoints.- A trial run used a sample of pure sodium carbon-
ate. How does the volume of acid necessary to
reach G from 0 compare to the volume of acid
necessary to get from G to H?
(A) They are the same.
(B) It takes more to reach point G.
(C) It takes more to get from G to H.
(D) It is impossible to determine.
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