Question

Silicon is produced for the chemical and electronics industries by the following reactions. Give the balanced equation for each reaction. a. \(\mathrm{SiO}_{2}(s)+\mathrm{C}(s) \frac{\text { Heemic }}{\text { ar thmace }} \mathrm{Si}(s)+\mathrm{CO}(g)\) b. Silicon tetrachloride is reacted with very pure magnesium, producing silicon and magnesium chloride. c. \(\mathrm{Na}_{2} \mathrm{SiF}_{6}(s)+\mathrm{Na}(s) \rightarrow \mathrm{Si}(s)+\mathrm{NaF}(s)\) 98\. Glass is a mixture of several compounds, but a major constituent of most glass is calcium silicate, \(\mathrm{CaSiO}_{3} .\) Glass can be etched by treatment with hydrofluoric acid; HF attacks the calcium silicate of the glass, producing gaseous and water-soluble products (which can be removed by washing the glass). For example, the volumetric glassware in chemistry laboratories is often graduated by using this process. Balance the following equation for the reaction of hydrofluoric acid with calcium silicate. $$ \mathrm{CaSiO}_{3}(s)+\mathrm{HF}(a q) \longrightarrow \mathrm{CaF}_{2}(a q)+\mathrm{SiF}_{4}(g)+\mathrm{H}_{2} \mathrm{O}(l) $$

Short answer

The balanced equations for the mentioned reactions are: a. \(\mathrm{SiO}_{2}(s) + \mathrm{C}(s) \rightarrow \mathrm{Si}(s) + 2\mathrm{CO}(g)\) b. \(\mathrm{SiCl}_{4}(g) + 2\mathrm{Mg}(s) \rightarrow \mathrm{Si}(s) + 2\mathrm{MgCl}_{2}(s)\) c. \(\mathrm{Na}_{2} \mathrm{SiF}_{6}(s) + \mathrm{Na}(s) \rightarrow \mathrm{Si}(s) + 3\mathrm{NaF}(s)\) 98. \( \mathrm{CaSiO}_{3}(s) + 4\mathrm{HF}(a q) \longrightarrow \mathrm{CaF}_{2}(a q) + \mathrm{SiF}_{4}(g) + \mathrm{H}_{2} \mathrm{O}(l)\)

Step-by-step solution

Count atoms on both sides of the equation

First count the number of atoms for each element on both the reactants and products side: Reactants: 1 Si, 2 O, and 1 C. Products: 1 Si, 1 O, and 1 C.

Balance the equation

Since there are two oxygen atoms on the reactant side, but only one on the product side, we need to add a 2 in front of \(\mathrm{CO}(g)\): \(\mathrm{SiO}_{2}(s) + \mathrm{C}(s) \rightarrow \mathrm{Si}(s) + 2\mathrm{CO}(g)\) Now, the equation is balanced with 1 Si, 2 O, and 1 C on both sides. b. Balance the reaction of silicon tetrachloride with very pure magnesium

Write the unbalanced equation

We need to write the unbalanced equation for the reaction of silicon tetrachloride (\(\mathrm{SiCl}_{4}\)) with magnesium (Mg), producing silicon (Si) and magnesium chloride (MgCl₂): \(\mathrm{SiCl}_{4}(g) + \mathrm{Mg}(s) \rightarrow \mathrm{Si}(s) + \mathrm{MgCl}_{2}(s)\)

Balance the equation

Count the number of atoms for each element on both sides: Reactants: 1 Si, 4 Cl, and 1 Mg. Products: 1 Si, 2 Cl, and 1 Mg. We need to balance the number of Cl atoms, so we add a 2 in front of \(\mathrm{MgCl}_{2}(s)\) and also need to put a 2 in front of the \(\mathrm{Mg}(s)\): \(\mathrm{SiCl}_{4}(g) + 2\mathrm{Mg}(s) \rightarrow \mathrm{Si}(s) + 2\mathrm{MgCl}_{2}(s)\) Now, the equation is balanced with 1 Si, 4 Cl, and 2 Mg on both sides. c. Balance the reaction of \(\mathrm{Na}_{2} \mathrm{SiF}_{6}(s) + \mathrm{Na}(s) \rightarrow \mathrm{Si}(s) + \mathrm{NaF}(s)\)

Count atoms on both sides of the equation

Count the number of atoms for each element on both the reactants and products side: Reactants: 2 Na, 1 Si, 6 F. Products: 1 Si, 1 Na, and 1 F.

Balance the equation

Add a 3 in front of \(\mathrm{NaF}(s)\) to balance Na and F: \(\mathrm{Na}_{2} \mathrm{SiF}_{6}(s) + \mathrm{Na}(s) \rightarrow \mathrm{Si}(s) + 3\mathrm{NaF}(s)\) Now, the equation is balanced with 1 Si, 3 Na, and 6 F on both sides. 98. Balance the reaction of \(\mathrm{CaSiO}_{3}(s) + \mathrm{HF}(a q) \longrightarrow \mathrm{CaF}_{2}(a q) + \mathrm{SiF}_{4}(g) + \mathrm{H}_{2} \mathrm{O}(l)\)

Count atoms on both sides of the equation

Count the number of atoms for each element on both the reactants and products side: Reactants: 1 Ca, 1 Si, 3 O, 1 H, 1 F. Products: 1 Ca, 1 Si, 1 O, 2 H, 6 F.

Balance the equation

Add a 4 in front of \(\mathrm{HF}(a q)\): \(\mathrm{CaSiO}_{3}(s) + 4\mathrm{HF}(a q) \longrightarrow \mathrm{CaF}_{2}(a q) + \mathrm{SiF}_{4}(g) + \mathrm{H}_{2} \mathrm{O}(l)\) Now the equation is balanced with 1 Ca, 1 Si, 3 O, 4 H, and 6 F on both sides.

Key concepts

Silicon production

Silicon is an essential element used in various industries, from electronics to chemicals. Its production often begins with the reduction of silicon dioxide (\(\mathrm{SiO}_2\)). In its natural state, silicon dioxide is found abundantly in sand. By heating silicon dioxide with carbon (\(\mathrm{C}\)) in an electric arc furnace, silicon (\(\mathrm{Si}\)) is produced along with carbon monoxide (\(\mathrm{CO}\)), a gaseous byproduct.

The reaction can be represented as follows:

• Reactants: \(\mathrm{SiO}_{2}(s) + \mathrm{C}(s)\)
• Products: \(\mathrm{Si}(s) + \mathrm{CO}(g)\)

To balance this equation, it is crucial to ensure that the number of oxygen atoms on the reactant side equals those on the product side by putting a coefficient of 2 in front of \(\mathrm{CO}\). This leads to the balanced equation: \[\mathrm{SiO}_{2}(s) + \mathrm{C}(s) \rightarrow \mathrm{Si}(s) + 2\mathrm{CO}(g)\]
This process is essential in producing silicon for further chemical reactions.

Silicon tetrachloride reaction

Silicon tetrachloride (\(\mathrm{SiCl}_{4}\)) reacts with magnesium (\(\mathrm{Mg}\)) to produce pure silicon, an essential component in manufacturing electronics. In this reaction, silicon tetrachloride serves as the source of silicon.

Initially, an unbalanced chemical equation for this reaction is: \[\mathrm{SiCl}_{4}(g) + \mathrm{Mg}(s) \rightarrow \mathrm{Si}(s) + \mathrm{MgCl}_{2}(s)\]
To balance the reaction, we must ensure that the number of chlorine (\(\mathrm{Cl}\)) and magnesium molecules are equal on both sides. By placing a coefficient of 2 in front of \(\mathrm{Mg}\) and \(\mathrm{MgCl}_{2}\), we maintain balance.

The balanced equation becomes: \[\mathrm{SiCl}_{4}(g) + 2\mathrm{Mg}(s) \rightarrow \mathrm{Si}(s) + 2\mathrm{MgCl}_{2}(s)\]
This balanced reaction ensures equal distribution of atoms, thereby conserving mass according to the law of conservation of mass, a fundamental principle in stoichiometry.

Hydrofluoric acid and glass etching

Glass etching is a process used to produce patterns on glass by eroding its surface. Hydrofluoric acid (HF) plays a crucial role in this process. When hydrofluoric acid interacts with calcium silicate (\(\mathrm{CaSiO}_{3}\)), a primary component of many glasses, a chemical reaction occurs.

This reaction produces calcium fluoride (\(\mathrm{CaF}_{2}\)), silicon tetrafluoride (\(\mathrm{SiF}_{4}\)), and water (\(\mathrm{H}_{2}\mathrm{O}\)), all of which are either gaseous or water-soluble products, allowing them to be easily washed away. The chemical equation for this process is: \[\mathrm{CaSiO}_{3}(s) + \mathrm{HF}(aq) \rightarrow \mathrm{CaF}_{2}(aq) + \mathrm{SiF}_{4}(g) + \mathrm{H}_{2}\mathrm{O}(l)\]

The challenge in balancing the reaction lies in ensuring an equal number of atoms for each element on both sides. After counting and comparing atoms, we adjust the equation by placing a coefficient of 4 in front of HF: \[\mathrm{CaSiO}_{3}(s) + 4\mathrm{HF}(aq) \rightarrow \mathrm{CaF}_{2}(aq) + \mathrm{SiF}_{4}(g) + \mathrm{H}_{2}\mathrm{O}(l)\]
By balancing the equation, we respect stoichiometry's rules, providing a clear path from reactants to products.

Stoichiometry

Stoichiometry is the section of chemistry that deals with the quantitative relationship between reactants and products in chemical reactions. It's a crucial concept for anyone learning to balance chemical equations.

In a balanced chemical equation, stoichiometry ensures that the number of atoms of each element is the same on both sides of the equation. This balance reflects the conservation of mass principle, which dictates that matter cannot be created or destroyed in a closed system.

To understand stoichiometry:

• Count the number of each type of atom on the reactant and product sides.
• Adjust coefficients before compounds to balance the number of atoms for each element.
• The coefficients indicate the ratio of moles of reactants to moles of products.

Mastery of stoichiometry is essential for predicting the quantities of products formed from given reactants or determining the amounts of reactants needed to form desired products. It's the mathematical backbone of chemistry, ensuring that reactions are predictable and efficient.