Question Video: Selecting the Incorrect Statement about the Electromotive Series | Nagwa Question Video: Selecting the Incorrect Statement about the Electromotive Series | Nagwa

Question Video: Selecting the Incorrect Statement about the Electromotive Series Chemistry • Third Year of Secondary School

The diagram shows the electromotive series. Which of the following statements about the electromotive series is not true? [A] Zinc metal is a better reducing agent than aluminum metal. [B] The more negative the standard reduction potential is, the stronger a reducing agent the metal is. [C] Lithium metal is a better reducing agent than gold metal. [D] Silver ions are better oxidizing agents than calcium ions. [E] The more positive the standard reduction potential is, the stronger an oxidizing agent the metal ion is.

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Video Transcript

The diagram shows the electromotive series. Which of the following statements about the electromotive series is not true? (A) Zinc metal is a better reducing agent than aluminum metal. (B) The more negative the standard reduction potential is, the stronger a reducing agent the metal is. (C) Lithium metal is a better reducing agent than gold metal. (D) Silver ions are better oxidizing agents than calcium ions. (E) The more positive the standard reduction potential is, the stronger an oxidizing agent the metal ion is.

In this question, we want to know which of the answers in the question is not true when investigating the electromotive series. The electromotive series is a sequence of elements that generally consists of metals that are arranged by their standard reduction potentials. Hydrogen is listed in the middle of the sequence with a value of 0.00 volts as it is the standard reference electrode used to determine the reduction potentials of other systems.

The standard reduction potential is measured under specific standard conditions. These are one-molar electrolyte solution concentrations, one-atmosphere pressure, and typically a temperature of 298 kelvin.

If we look at the direction of the arrow and the label, we can see that the elements above hydrogen have negative values and the ones below hydrogen in the sequence have positive standard reduction potential values.

The more negative or the lower the reduction potential of an element is, the less likely it is to be reduced. Lithium is more likely to be oxidized when in a galvanic cell with any element below it. And thus, lithium is a strong reducing agent.

The more positive or the higher the reduction potential, the more likely an element is to be reduced. In other words, a higher reduction potential indicates a greater capacity to receive electrons and be reduced. The elements below hydrogen, for example, silver, are more likely to be reduced when in a galvanic cell with any element above it in the series. Thus, these elements are weak reducing agents.

We can use this information to examine our answer choices.

Answer choice (A) states that zinc metal is a better reducing agent than aluminum metal. However, aluminum is above zinc in the electromotive series, which would mean that aluminum has a more negative standard reduction potential and is thus a stronger reducing agent than zinc. This statement is incorrect and is thus our answer, as we were asked which statement is not true. Let’s quickly check this by examining the remaining answers.

In answer choice (B), we are told that the more negative the standard reduction potential is, the stronger the reducing agent the metal or element is. This is a true statement, as we have seen. We can eliminate answer (B).

Statement (E) — the more positive the standard reduction potential is, the stronger an oxidizing agent the metal ion is — is the converse of statement (B) and thus must be true. So we can rule out answer (E) as well.

Answer choice (C), lithium metal is a better reducing agent than gold metal, is also true. We can see this in the circled portions. So we can eliminate this answer too.

Answer (D) says that silver ions are better oxidizing agents than calcium ions. Note, here we are talking about ions, not neutral metal atoms. This statement makes sense. Since elements lower on this list are weak reducing agents, silver ions will accept electrons more readily than calcium ions and are thus better oxidizing agents. Answer (D) is true, and we can eliminate it.

Finally, which statement about the electromotive series is not true? The answer is (A): zinc metal is a better reducing agent than aluminum metal.

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