Question 1

Which of the following statements best describes the role of the oxidizing agent in a redox reaction?

Accepted Answer

It accepts electrons from another species, causing that species to be oxidized.

Question 2

What is the oxidation state of chromium in $$\mathrm{Cr_2O_7$$^{2-}$$}$$?

Accepted Answer

$$+6$$

Question 3

Which of the following is the correct balanced half-reaction for the oxidation of $$\mathrm{Mn$$^{2+}$$} to$$ $$\mathrm{$$MnO_4$$^-} in $$acidic solution?

Accepted Answer

$$\mathrm{Mn$$^{2+}$$ (aq) + 4 H_2O (l) \rightarrow $$MnO_4$$^- (aq) + 8 H^+ (aq) + 5 e^-}$$

Question 4

In the reaction $$2\mathrm{Na} (s) + \mathrm{Cl_2$} (g) \rightarrow 2\mathrm{NaCl} (s)$$, which species is oxidized?

Accepted Answer

$$\mathrm{Na}$$

Question 5

Which rule is NOT correct for assigning oxidation numbers?

Accepted Answer

The oxidation state of hydrogen in metal hydrides is $$+1.$$

Question 6

When balancing a redox reaction in acidic solution, what is the correct order of steps?

Accepted Answer

Balance all atoms except H and O, then O with $$\mathrm{H_2O}$$, H with $$\mathrm{H^+}$$, and finally charge with $$e^-.$$

Question 7

In the reaction $$\mathrm{Cr(OH)_3 + ClO^- \rightarrow $$CrO_4$$^{2-} + Cl_2$} ($$basic solution), what is the correct way to neutralize $$\mathrm{H^+}$$ ions after balancing in acidic solution?

Accepted Answer

Add $$\mathrm{OH^-} to $$both sides of the equation.

Question 8

Which of the following best describes what happens to the oxidation state of an element during reduction?

Accepted Answer

It decreases due to gain of electrons.

Question 9

A student is asked to balance the following redox reaction in acidic solution: $$\mathrm{Cr_2O_7$$^{2-}$$ + CH_3OH \rightarrow HCO_2H + Cr$$^{3+}$$}. $$What is the first step?

Accepted Answer

Identify the redox pairs and split into half-reactions.

Question 10

Which of the following is a correct statement about the sum of oxidation numbers in a polyatomic ion?

Accepted Answer

It is equal to the charge of the ion.

Question 11

In the reaction $$\mathrm{2Al (s) + 3Cl_2 (g) \rightarrow 2AlCl_3 (s)}$$, what is the oxidation state of aluminum in $$\mathrm{$$AlCl_3$$}$$?

Accepted Answer

$$+3$$

Question 12

Which of the following is the correct balanced equation for the reduction half-reaction of $$\mathrm{Cl_2$} to$$ $$\mathrm{Cl^-}$$?

Accepted Answer

$$\mathrm{Cl_2$ (g) + 2 e^- \rightarrow 2 Cl^- (aq)}$$

Question 13

A redox reaction is balanced when:

Accepted Answer

The number of atoms of each element and the total charge are the same on both sides.

Question 14

Which of the following is the correct sequence for balancing a redox reaction in basic solution?

Accepted Answer

Balance as if in acidic solution, add $$\mathrm{OH^-} to $$both sides to neutralize $$\mathrm{H^+}$$, combine $$\mathrm{H^+}$$ and $$\mathrm{OH^-} to $$form $$\mathrm{H_2O}$$, and simplify.

Question 15

In the reaction $$\mathrm{NO_2$^- (aq) + Al (s) \rightarrow $$AlO_2$$^- (aq) + NH_3$ (g)} ($$basic solution), which species is reduced?

Accepted Answer

$$\mathrm{NO_2$^-}$$

Electrochemistry: Redox Reactions and Balancing Equations

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