Using Experimental Results to Rank Oxidizing and Reducing Agents

Identification of Species and Chemical Roles

• Spectator Ions: In the provided experiment, metal nitrate compounds are used. The nitrate ions ($NO_3^-$) act as spectator ions, meaning they do not participate in the chemical reaction. To simplify the analysis, the nitrates are discarded, and the substances are expressed as cations.
• Charge Determination: Nitrate ($NO_3$) carries a $-1$ charge. The charge of the metal cation is determined by the number of nitrate ions in the compound:
  • $Dy(NO_3)_2$: Contains two nitrates, resulting in a cation of $Dy^{2+}$.
  • $Be(NO_3)_2$: Contains two nitrates, resulting in a cation of $Be^{2+}$.
  • $Gd(NO_3)_3$: Contains three nitrates, resulting in a cation of $Gd^{3+}$.
  • $Ti(NO_3)_3$: Contains three nitrates, resulting in a cation of $Ti^{3+}$.
• Defining Oxidizing and Reducing Agents:
  • Oxidizing Agent (OA): The more positive form of the element (the cations in this experiment: $Dy^{2+}$, $Be^{2+}$, $Gd^{3+}$, and $Ti^{3+}$).
  • Reducing Agent (RA): The less positive or neutral form of the element (the neutral metals in this experiment: $Dy$, $be$, $GD$, and $TI$).
• Half-Reaction Structure: In a standard reduction table, reduction half-reactions are written with the oxidizing agent on the left side gaining electrons to form the reducing agent on the right side. The general format is:
  • $Oxidizing \, Agent + n e^- \rightarrow Reducing \, Agent$

Experimental Observations and Analysis

Experimental evidence is used to build a hierarchy of reactivity. The core rule for spontaneity in a reduction table is that any oxidizing agent on the left will react spontaneously with any reducing agent on the right that is positioned below it.

• Observation 1: $Be(NO_3)_2$ solution react spontaneously with $Dy$ metal:
  • Since $Be(NO_3)_2$ is the source of the $Be^{2+}$ ion (OA) and it reacts with $Dy$ metal (RA), $Be^{2+}$ must be placed higher on the left side of the table than $Dy$ is on the right side.
• Observation 2: No reaction between $Gd(NO_3)_3$ solution and $Dy$ metal:
  • $Gd(NO_3)_3$ provides the $Gd^{3+}$ ion (OA). Because there is no reaction with $Dy$ metal (RA), the spontaneity rule is not met. Therefore, $Gd^{3+}$ must be placed below $Dy$ on the reduction table.
• Observation 3: $be$ metal reacts spontaneously with the $Ti(NO_3)_3$ solution:
  • $Ti(NO_3)_3$ provides the $Ti^{3+}$ ion (OA). Since it reacts spontaneously with $be$ metal (RA), the $Ti^{3+}$ ion must be placed above $be$ on the reduction table.

Constructing the Mini Reduction Table

By synthesizing the observations above, we can arrange the four half-reactions in order of decreasing reduction potential (from strongest oxidizing agent at the top to weakest at the bottom):

1. $Ti^{3+} + 3e^- \rightarrow TI$
2. $Be^{2+} + 2e^- \rightarrow be$
3. $Dy^{2+} + 2e^- \rightarrow Dy$
4. $Gd^{3+} + 3e^- \rightarrow GD$

Ranking Oxidizing and Reducing Agents

Oxidizing Agents (Left Side of Table)

On a reduction table, the strength of the oxidizing agents increases as you move up the left side. Based on the constructed table, the ranking of the four oxidizing agents from strongest to weakest is:

1. $Ti^{3+}$ (Strongest)
2. $Be^{2+}$
3. $Dy^{2+}$
4. $Gd^{3+}$ (Weakest)

In shorthand notation: $Ti^{3+} > Be^{2+} > Dy^{2+} > Gd^{3+}$.

Reducing Agents (Right Side of Table)

The strength of reducing agents increases as you move down the right side of the table. Based on the constructed table, the ranking of the four reducing agents from strongest to weakest is:

1. $GD$ (Strongest)
2. $Dy$
3. $be$
4. $TI$ (Weakest)

In shorthand notation: $GD > Dy > be > TI$.