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) TiCl4 + 2 Mg → Ti + 2 MgCl2 (b) Mg is oxidized, TiCl4 is reduced. (c) Mg is the reductant, TiCl4 is the oxidant.

Step-by-step solution

Writing the balanced chemical equation

First, let's write down the reactants and products given in the problem. Reactants: titanium tetrachloride (TiCl4) and magnesium (Mg) Products: titanium (Ti) and magnesium chloride (MgCl2) Next, we'll write down the unbalanced chemical equation: TiCl4 + Mg → Ti + MgCl2 In order to balance the equation, we need to match the number of atoms of all elements on both sides of the reaction. TiCl4 has 1 Ti atom and 4 Cl atoms. Mg has 1 Mg atom. On the product side, Ti has 1 Ti atom, and MgCl2 has 1 Mg atom and 2 Cl atoms. By observing the species present, if we double the amount of MgCl2, the Cl atoms count will balance. TiCl4 + Mg → Ti + 2 MgCl2 Now, we have a balanced chemical equation: TiCl4 + 2 Mg → Ti + 2 MgCl2

Identifying oxidation and reduction

Oxidation is the process of losing electrons, and reduction is the process of gaining electrons. To find out which species is being oxidized or reduced, we need to determine the changes in the oxidation states between the reactants and products. TiCl4: Ti has an oxidation state of +4 (as it is sharing its 4 electrons with the four Cl atoms) Mg: Oxidation state is 0 Ti : Oxidation state is 0 MgCl2: Mg has an oxidation state of +2 (it gave its 2 electrons to the two Cl atoms) Now, comparing the oxidation states between reactants and products: - Ti goes from +4 in TiCl4 to 0 in Ti, which means Ti gains 4 electrons (reduction) - Mg goes from 0 to +2 in MgCl2, which means Mg loses 2 electrons (oxidation)

Identifying the reductant and oxidant

The reductant is the substance that loses electrons and gets oxidized, while the oxidant is the substance that gains electrons and gets reduced. In this case, magnesium (Mg) is being oxidized, meaning it loses electrons. Therefore, Mg is the reductant. Titanium tetrachloride (TiCl4) is being reduced (gaining electrons), so TiCl4 is the oxidant. In summary, (a) The balanced chemical equation for the reaction is: TiCl4 + 2 Mg → Ti + 2 MgCl2 (b) Magnesium (Mg) is being oxidized, and titanium tetrachloride (TiCl4) is being reduced. (c) The reductant is magnesium (Mg), and the oxidant is titanium tetrachloride (TiCl4).

Key concepts

Balancing Chemical Equations

Balancing chemical equations is a crucial skill in chemistry that ensures the law of conservation of mass is respected, meaning that the number of atoms of each element is the same on both sides of the equation. Let's delve into the process of balancing the equation TiCl4 + Mg → Ti + 2 MgCl2.

When balancing, start by listing the number of atoms of each element in the reactants and products. In our problem, we have titanium, chlorine, and magnesium to consider. The initial equation shows that chlorine is out of balance, with 4 atoms on the reactant side and only 2 on the product side. By doubling the amount of MgCl2, you balance the chlorine atoms. The titanium and magnesium atoms are already balanced—one atom each on both sides.

Thus, the corrected equation becomes TiCl4 + 2 Mg → Ti + 2 MgCl2, with equal numbers of each type of atom on either side, reflecting the mass conservation principle.

Oxidation States

Understanding oxidation states is key to grasping redox reactions. The oxidation state, often referred to as oxidation number, is a measure of the degree of oxidation of an atom in a substance. It helps us track the transfer of electrons during the reaction.

In our reaction, TiCl4 has a titanium (Ti) atom with an oxidation state of +4 and chlorine (Cl) with -1 each, summing to zero. Magnesium (Mg) in its elemental form has an oxidation state of 0, while in MgCl2, magnesium exhibits a +2 oxidation state because it has lost two electrons, and each chlorine has an oxidation state of -1. By comparing these states, we can see that Ti is reduced as it goes from +4 to 0, and Mg is oxidized as it goes from 0 to +2, indicating that the transfer of electrons is indeed occurring.

Identifying Reductant and Oxidant

In redox chemistry, identifying the reductant and oxidant is fundamental. The reductant (also known as the reducing agent) is the substance that donates electrons, thus being oxidized itself. Conversely, the oxidant (oxidizing agent) accepts electrons, undergoing reduction.

In the given equation, magnesium's oxidation state increases from 0 to +2, indicating it loses electrons and, hence, is the reductant. Titanium tetrachloride, on the other side, gains electrons as Ti's oxidation state decreases from +4 in TiCl4 to 0 in Ti, making TiCl4 the oxidant. Understanding the role of each substance in a redox reaction is essential, as it lays the groundwork for predicting reaction outcomes and crafting further chemical equations.