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Chapter 20: Problem 21

The purification process of silicon involves the reaction of silicon tetrachloride vapor \(\left(\mathrm{SiCl}_{4}(g)\right)\) with hydrogen to \(1250^{\circ} \mathrm{C}\) to form solid silicon and hydrogen chloride. \((\mathbf{a})\) 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

Expert verified
The balanced chemical equation for the reaction is: \[\mathrm{SiCl}_{4}(g) + 2\mathrm{H}_{2}(g) \rightarrow \mathrm{Si}(s) + 4\mathrm{HCl}(g)\]. Silicon in \(\mathrm{SiCl}_{4}\) is reduced (oxidation state decreases from +4 to 0), while hydrogen in \(\mathrm{H}_{2}\) is oxidized (oxidation state increases from 0 to +1). Silicon tetrachloride \(\mathrm{SiCl}_{4}\) is the oxidant, and hydrogen gas \(\mathrm{H}_{2}\) is the reductant.

Step by step solution

01

Write the balanced chemical equation for the reaction

To write the balanced chemical equation, we begin by writing down the reactants and products, then balance the number of atoms for each element in the reaction. Reactants: \(\mathrm{SiCl}_{4}(g)\) and \(\mathrm{H}_{2}(g)\) Products: Solid silicon (Si) and hydrogen chloride (HCl) Now, let's balance the equation: \[\mathrm{SiCl}_{4}(g) + 2\mathrm{H}_{2}(g) \rightarrow \mathrm{Si}(s) + 4\mathrm{HCl}(g)\]
02

Identify the substances being oxidized and reduced

Oxidation and reduction refer to the change in oxidation states of elements in a reaction. If the oxidation state of an element increases, it is being oxidized, whereas if it decreases, it is being reduced. - In \(\mathrm{SiCl}_4\), the oxidation state of silicon (Si) is +4. - In \(\mathrm{H}_{2}\), the oxidation state of hydrogen (H) is 0. - In \(\mathrm{HCl}\), the oxidation state of hydrogen is +1. Comparing the oxidation states, we see that silicon's oxidation state has decreased from +4 to 0, implying it has been reduced. On the other hand, hydrogen's oxidation state has increased from 0 to +1, implying it has been oxidized.
03

Identify the reductant and oxidant

In a redox reaction, the substance that causes another substance to be reduced is called the oxidant, while the substance causing another substance to be oxidized is called the reductant. From Step 2, silicon is being reduced, which indicates that silicon tetrachloride (\(\mathrm{SiCl}_{4}(g)\)) is the oxidant. Hydrogen is being oxidized, which indicates that hydrogen gas (\(\mathrm{H}_{2}(g)\)) is the reductant.

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Most popular questions from this chapter

(a) Aluminum metal is used as a sacrificial anode to protect offshore pipelines in salt water from corrosion. Why is the aluminum referred to as a "sacrificial anode"? (b) Looking in Appendix E, suggest what metal the pipelines could be made from in order for aluminum to be successful as a sacrificial anode.

A voltaic cell consists of a strip of cadmium metal in a solution of \(\mathrm{Cd}\left(\mathrm{NO}_{3}\right)_{2}\) in one beaker, and in the other beaker a platinum electrode is immersed in a NaCl solution, with \(\mathrm{Cl}_{2}\) gas bubbled around the electrode. A salt bridge connects the two beakers. (a) Which electrode serves as the anode, and which as the cathode? (b) Does the Cd electrode gain or lose mass as the cell reaction proceeds? (c) Write the equation for the overall cell reaction. (d) What is the emf generated by the cell under standard conditions?

A cell has a standard cell potential of \(+0.257 \mathrm{~V}\) at $298 \mathrm{~K}$. What is the value of the equilibrium constant for the reaction \((\mathbf{a})\) if \(n=1 ?(\mathbf{b})\) if \(n=2 ?(\mathbf{c})\) if \(n=3 ?\)

Consider the following table of standard electrode potentials for a series of hypothetical reactions in aqueous solution: $$ \begin{array}{lr} \hline \text { Reduction Half-Reaction } & {E^{\circ}(\mathrm{V})} \\ \hline \mathrm{A}^{+}(a q)+\mathrm{e}^{-} \longrightarrow \mathrm{A}(s) & 1.33 \\\ \mathrm{~B}^{2+}(a q)+2 \mathrm{e}^{-} \longrightarrow \mathrm{B}(s) & 0.87 \\\ \mathrm{C}^{3+}(a q)+\mathrm{e}^{-} \longrightarrow \mathrm{C}^{2+}(a q) & -0.12 \\ \mathrm{D}^{3+}(a q)+3 \mathrm{e}^{-} \longrightarrow \mathrm{D}(s) & -1.59 \\\ \hline \end{array} $$ (a) Which substance is the strongest oxidizing agent? Which is weakest? (b) Which substance is the strongest reducing agent? Which is weakest? (c) Which substance(s) can oxidize \(\mathrm{C}^{2+} ?\)

A voltaic cell similar to that shown in Figure 20.5 is constructed. One half- cell consists of an iron strip placed in a solution of \(\mathrm{FeSO}_{4}\), and the other has an aluminum strip placed in a solution of \(\mathrm{Al}_{2}\left(\mathrm{SO}_{4}\right)_{3} .\) The overall cell reaction is $$ 2 \mathrm{Al}(s)+3 \mathrm{Fe}^{2+}(a q) \longrightarrow 3 \mathrm{Fe}(s)+2 \mathrm{Al}^{3+}(a q) $$ (a) What is being oxidized, and what is being reduced? (b) Write the half- reactions that occur in the two half-cells. (c) Which electrode is the anode, and which is the cathode? (d) Indicate the signs of the electrodes. (e) Do electrons flow from the aluminum electrode to the iron electrode or from the iron to the aluminum? (f) In which directions do the cations and anions migrate through the solution? Assume the \(\mathrm{Al}\) is not coated with its oxide.
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