Use the unbalanced redox reaction below to answer questions 6-8 Fe(s) + CrO_4^2-

Question

Use the unbalanced redox reaction below to answer questions 6-8 Fe(s) + CrO_4^2-(aq) rightarrow Fe^3+ CrO_2(aq) (basic media) The oxidation state of Chromium changes from ______ to _____. a. 4 to 0 b. 6 to 4 c. 6 to 2 d. 6 to 5 e. 4 to 2 The reducing agent is agent is _____. a. CrO_4^2-(aq) b. Fe^3+ c. CrO_2(aq) d. Fe(s) When the equation is balanced the coefficient in front of OH is a. 12 b. 16 c. 14 d. 10 e 8 When the standard free energy of a reaction Delta G degree is negative we know which of the following is always true? A. The entropy of the universe is increasing. B. The Delta H degree is negative C. The Delta S degree_system is positive D. K_ed > 1 A. A only B. A& D only C. B & C only D. A& B only E. all are true

Explanation / Answer

Balance

Fe = Fe+3

CrO4-2 = CrO2

balance O

Fe = Fe+3

CrO4-2 = CrO2 + 2H2O

balnace H

Fe = Fe+3

4H+ + CrO4-2 = CrO2-2 + 2H2O

balance charge

Fe = Fe+3 + 3e-

4e- + 4H+ + CrO4-2 = CrO2-2 + 2H2O

balance e-

4Fe = 4Fe+3 + 12e-

12e- + 12H+ + 3CrO4-2 = 3CrO2-2 + 12H2O

add all

4Fe + 12H+ + 3CrO4-2 = 3CrO2-2 + 12H2O +  4Fe+3

add OH-

4Fe + 12H2O + 3CrO4-2 = 3CrO2-2 + 12OH- +  4Fe+3

now,

Cr goes from +6 to +2

Q7.

reducing agent --> is oxidizing so choose Fe(s)

Q8

OH -- 12 coefficient

Q9.

dG < 0

then

entropy always increaes, dH cna't be sure, dSsystem cant be sure, KEq > 1

so only A and D are true

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