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Posted by on Friday, May 2, 2014 at 11:10pm.

1) Assuming the following reaction proceeds in the forward direction,
3 Sn4+(aq) + 2 Cr(s) ---> 3 Sn2+(aq) + 2 Cr3+(aq)
a.Sn4+(aq) is the reducing agent and Cr(s) is the oxidizing agent.

b.Cr(s) is the reducing agent and Sn2+(aq) is the oxidizing agent.

c.Sn4+(aq) is the reducing agent and Sn2+(aq) is the oxidizing agent.

d.Cr(s) is the reducing agent and Cr3+(aq) is the oxidizing agent.

e.Cr(s) is the reducing agent and Sn4+(aq) is the oxidizing agent.

The answer C




2) Write a balanced chemical equation for the oxidation of Cd(s) by concentrated nitric acid, producing NO2(g) and Cd2+(aq).
a. HNO3(aq) + Cd(s) ---> Cd2+(aq) + NO2(g) + OH–(aq)
b. 2 HNO3(aq) + Cd(s) ---> Cd2+(aq) + 2 NO2(g) + 2 OH–(aq)
c. HNO3(aq) + Cd(s) + H+(aq) ---> Cd2+(aq) + NO2(g) + H2O()
d. 4 HNO3(aq) + Cd(s) ---> Cd2+(aq) + 2 NO2(g) + 2H2O() + 2 NO3–(aq)
e. HNO3(aq) + Cd(s) ---> Cd2+(aq) + NO2(g)


the answer is D



3) Consider the following half-reactions:
Cl2(g) + 2 e– -> 2 Cl–(aq) E = +1.36 V
Ag+(aq) + e– -> Ag(s) E = +0.80 V
Cu2+(aq) + 2 e– -> Cu(s) E = +0.34 V
Sn2+(aq) + 2 e– -> Sn(s) E = –0.14 V
Al3+(aq) + 3 e– -> Al(s) E = –1.66 V
Which of the above elements or ions will reduce Cu2+(aq)?
a. Ag(s) and Sn2+(aq)
b. Cl–(aq) and Ag(s)
c. Cl2(g) and Ag+(aq)
d. Sn(s) and Al(s)
e. Sn2+(aq) and Al3+(aq)

the answer is D


4)Given the following two half-reactions, write the overall balanced reaction in the direction in which it is spontaneous and calculate the standard cell potential.
Ga3+(aq) + 3 e– -> Ga(s) E = –0.53 V
Sn4+(aq) + 2 e– -> Sn2+(aq) E = +0.15 V
a. 2 Ga3+(aq) + 3 Sn2+(aq) -> 2 Ga(s) + 3 Sn4+(aq) = +0.68 V
b. 3 Ga3+(aq) + 2 Sn2+(aq) ->3 Ga(s) + 2 Sn4+(aq) = –1.89 V
c. 2 Ga(s) + 3 Sn4+(aq) -> 2 Ga3+(aq) + 3 Sn2+(aq) = +0.68 V
d. 3 Ga(s) + 2 Sn4+(aq) -> 3 Ga3+(aq) + 2 Sn2+(aq) = +0.38 V
e. 2 Ga(s) + 3 Sn4+(aq) -> 2 Ga3+(aq) + 3 Sn2+(aq) = +1.89 V

the answer is D

  • Chem Check Please!!! - , Friday, May 2, 2014 at 11:54pm

    1. Cris, I don't agree with C as an answer. Here is the way you keep these straight. Just remember the definition of oxidation and reduction.
    Oxidation is the loss of electrons.
    Reduction is the gain of electrons.
    The substance oxidized is the reducing agent.
    The substance reduced is the oxidizing agent.

  • Chem Check Please!!! - , Saturday, May 3, 2014 at 12:14am

    2 is ok
    3 is ok
    I don't agree with 4.

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