Question 1

In the first image, a titration is being performed using potassium permanganate ($$KMnO_4) as $$the titrant. What is the most likely reason the solution in the flask turns purple at the endpoint?

Accepted Answer

All the iron(II) ions have been oxidized, and excess $$KMnO_4$$ remains unreacted.

Question 2

Which balanced equation represents the reaction between copper metal and concentrated nitric acid, as shown in the second image?

Accepted Answer

$$4 $$HNO_3$$(aq) + Cu(s) \rightarrow 2 NO_2$(g) + Cu(NO_3$)_2(aq) + 2 H_2O(l)$$

Question 3

When balancing redox reactions in acidic solution using the oxidation numbers method, which species can be added to balance hydrogen atoms?

Accepted Answer

$$H^+(aq)$$

Question 4

In the reaction $$MnO_4^-(aq) + 5$$ $$Fe^{2+}(aq) + 8 H^+(aq$$) \rightarrow $$Mn^{2+}(aq) + 5$$ $$Fe^{3+}(aq) + 4 H_2O(l$$)$$, how many electrons are transferred per $$MnO_4$$^-$$ ion?

Accepted Answer

$$5$$ electrons

Question 5

Which of the following is the correct half-reaction for the reduction of permanganate ion in acidic solution?

Accepted Answer

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

Question 6

A student is asked to balance the following redox reaction in basic solution: $$IO_3^-(aq) + 3 C_2O$$_$$4^{2-}(aq) + 3 H_2O(l$$) \rightarrow I^-(aq) + 6 $$CO_2(g) + 6 OH^-(aq$$)$$. What is the total number of electrons transferred in this reaction?

Accepted Answer

$$6$$ electrons

Question 7

Which step is unique to balancing redox reactions in basic solution compared to acidic solution?

Accepted Answer

Adding $$OH^-(aq)$$ ions to both sides to neutralize $$H^+(aq)$$ ions.

Question 8

In the reaction $$4 $$HNO_3$$(aq) + Cu(s) \rightarrow 2 NO_2$(g) + Cu(NO_3$)_2(aq) + 2 H_2O(l)$$, what is the oxidation number change for copper?

Accepted Answer

From $$0 to$$ $$+2$$

Question 9

Which of the following best describes why the sum of the charges on both sides of a balanced redox equation must be equal?

Accepted Answer

Because charge is conserved during chemical reactions.

Question 10

A chemist uses the half-reactions method to balance the reaction $$Zn(s) + H^+(aq) \rightarrow Zn$$^{2+}$$(aq) + H_2$(g). $$What is the oxidation half-reaction?

Accepted Answer

$$Zn(s) \rightarrow Zn$$^{2+}$$(aq) + 2 e^-$$

Question 11

Which of the following is a correct statement about the use of potassium permanganate ($$KMnO_4) in $$redox titrations?

Accepted Answer

It acts as an oxidizing agent and its purple color signals the endpoint.

Question 12

In a redox reaction, which of the following indicates that a species has been oxidized?

Accepted Answer

Its oxidation number increases.

Question 13

When balancing the following reaction in acidic solution: $$MnO_4^-(aq) + Br^-(aq$$) \rightarrow $$MnO_2(s$$) + $$BrO_3^-(aq$$)$$, which species should be added to balance the hydrogen atoms?

Accepted Answer

$$H^+(aq)$$

Question 14

A student is asked to balance the following equation in basic solution: $$MnO_4^-(aq$$) + $$SO_3$$^{2-}(aq) \rightarrow $$SO_4$$^{2-}(aq) + $$MnO_2(s$$)$$. Which of the following steps is necessary?

Accepted Answer

Add $$OH^-(aq)$$ ions to both sides to neutralize $$H^+(aq)$$ ions.

Question 15

Which of the following is the correct reduction half-reaction for the conversion of $$Cr_2O_7$$^{2-}$$ to Cr$$^{3+}$$ in acidic solution?

Accepted Answer

$$Cr_2O_7$$^{2-}$$(aq) + 14 H^+(aq) + 6 e^- \rightarrow 2 Cr$$^{3+}$$(aq) + 7 H_2O(l)$$

Lesson 9.2: Balancing Redox Reaction Equations: Methods and Applications

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