Question

At \(900^{\circ} \mathrm{C},\) titanium tetrachloride vapor reacts with molten magnesium metal to form solid titanium metal and molten magnesium chloride. (a) Write a balanced equation for this reaction. (b) What is being oxidized, and what is being reduced? (c) Which substance is the reductant, and which is the oxidant?

Short answer

(a) The balanced equation for the reaction is: \(TiCl_4 + 2Mg \rightarrow Ti + 2MgCl_2\). (b) Titanium is being reduced, and magnesium is being oxidized. (c) Magnesium is the reductant and titanium tetrachloride is the oxidant.

Step-by-step solution

(a) Write a balanced equation

First, we need to identify the reactants and products: Reactants: Titanium tetrachloride (TiCl4) vapor and molten magnesium metal (Mg) Products: Solid titanium metal (Ti) and molten magnesium chloride (MgCl2) Now, we can write the unbalanced equation: TiCl4 + Mg -> Ti + MgCl2 We need to balance the equation by ensuring equal number of atoms of each element on both sides: TiCl4 + 2Mg -> Ti + 2MgCl2 Now, the equation is balanced with an equal number of atoms on both sides.

(b) Identify what is being oxidized and what is being reduced

To determine which species is being oxidized and which is being reduced, we need to find their oxidation states before and after the reaction: 1. Titanium (Ti) in TiCl4: +4 (since Cl has an oxidation number of -1) 2. Magnesium (Mg) in Mg: 0 (element in its elemental state has an oxidation number of 0) 3. Titanium (Ti) in Ti: 0 (element in its elemental state has an oxidation number of 0) 4. Magnesium (Mg) in MgCl2: +2 (since Cl has an oxidation number of -1) Now we can identify the changes in oxidation numbers: - Ti undergoes a reduction in its oxidation state from +4 to 0. - Mg undergoes an increase in its oxidation state from 0 to +2. So, titanium is being reduced, and magnesium is being oxidized.

(c) Identify the reductant and the oxidant

Based on the changes in the oxidation states, we can now identify the reductant and the oxidant: Reductant: The reductant is the substance that causes the reduction of another species by giving away electrons. In this reaction, magnesium (Mg) is the reductant, as it gives away two electrons causing the reduction of titanium. Oxidant: The oxidant is the substance that causes the oxidation of another species by gaining electrons. In this reaction, titanium tetrachloride (TiCl4) is the oxidant, as it gains two electrons causing the oxidation of magnesium.

Key concepts

Oxidation

In redox reactions, oxidation refers to the process in which a chemical species loses electrons. This change results in an increase in the oxidation number of the element involved. In simpler terms, when something gets oxidized, it is effectively giving away electrons to other substances.
In the original exercise, magnesium (Mg) metal undergoes oxidation. Initially, magnesium is in its elemental form. This means it has an oxidation number of zero. However, after the reaction, magnesium becomes part of magnesium chloride (MgCl2). In this compound, magnesium has an oxidation number of +2, indicating it has lost two electrons during the process.
Oxidation can be remembered using the helpful acronym "OIL RIG" – Oxidation Is Loss of electrons, Reduction Is Gain of electrons. This aids in quickly recalling what happens during an oxidation process in any redox reaction.

Reduction

Reduction is the opposite process of oxidation. It involves the gain of electrons by a chemical species, resulting in a decrease in its oxidation number. Reduction is essentially the "receiving" end in a redox reaction, where a substance gains electrons and thus becomes reduced.
In the given reaction of titanium tetrachloride with magnesium, titanium is the element undergoing reduction. Initially, in its compound form TiCl4, titanium has an oxidation state of +4. After the reaction, titanium is reduced to its elemental state, Ti, with an oxidation number of 0. This clearly shows that titanium has gained electrons in the reaction process.
A good way to remember reduction is the other part of the "OIL RIG" acronym – Reduction Is Gain (of electrons). This helps emphasize that reduction is all about electron gain in chemical reactions.

Chemical Equation Balancing

Balancing chemical equations is crucial for accurately describing the quantitative relationships in chemical reactions. It ensures the law of conservation of mass is satisfied, meaning that the number of atoms for each element is the same on both the reactant and product sides of the equation.
In the initial exercise, the unbalanced equation is listed as TiCl4 + Mg → Ti + MgCl2. Here, it's important to adjust coefficients to have equal numbers of each type of atom on both sides.

• Titanium (Ti): Already balanced with one atom on both sides.
• Chlorine (Cl): Four atoms on the left (in TiCl4), two on the right, so multiply MgCl2 by 2 to have 4 atoms.
• Magnesium (Mg): Now appears twice as MgCl2 on the right, necessitating two Mg atoms on the left to balance it.

Updating these coefficients leads to the balanced equation:\[ \text{TiCl}_4 + 2\text{Mg} \rightarrow \text{Ti} + 2\text{MgCl}_2 \]
Balancing chemical equations accurately is a foundational skill in chemistry that provides insights into the stoichiometry and dynamics of reactions.