Stoichiometry Silicon to be used in computer chips is manufactured in a process represented by the following reaction: SiCl4(l) + 2Mg(s) → Si(s)+2MgCl2(s) A sample of 225 g of silicon tetrachloride, SiCl4, is reacted with an excess (more than necessary) of Mg. How many moles of Si are produced?

Question

Stoichiometry
Silicon to be used in computer chips is manufactured in a process represented by the following reaction:

[latex]\underset{\substack{ ext{Silicon}\ ext{tetrachloride}}}{ ext{SiCl}_{4}(\ell)} + 2 ext{Mg(s)} \longrightarrow ext{Si(s)} + \underset{\substack{ ext{Magnesium}\ ext{chloride}}}{2 ext{MgCl}_{2} ext{(s)}}[/latex]

A sample of 225 g of silicon tetrachloride, [latex] ext{SiCl}_{4}[/latex], is reacted with an excess (more than necessary) of Mg. How many moles of Si are produced?

Strategy
To solve this example, we first convert grams of [latex] ext{SiCl}_{4}[/latex] to moles of [latex] ext{SiCl}_{4}[/latex], then moles of [latex] ext{SiCl}_{4}[/latex] to moles of Si.

Accepted Answer

Step 1: First, we convert grams of [latex] ext{SiCl}_{4}[/latex] to moles of [latex] ext{SiCl}_{4}[/latex]. For this calculation, we use the conversion factor 1 mol [latex] ext{SiCl}_{4}[/latex] = 170 g [latex] ext{SiCl}_{4}[/latex].
Step 2: To convert moles of [latex] ext{SiCl}_{4}[/latex] to moles of Si, use the conversion factor 1 mol [latex] ext{SiCl}_{4}[/latex] = 1 mol Si, which we obtain from the balanced chemical equation. Now we do the arithmetic and obtain the answer:

[latex]225\ ext{g SiCl}_{4} imes \frac{1\ \cancel{ ext{mol SiCl}_{4}}}{170\ \cancel{ ext{g SiCl}_{4}}} imes \frac{1\ ext{mol Si}}{1\ \cancel{ ext{mol SiCl}_{4}}} = 1.32\ ext{mol Si}[/latex]

■ Quick Check 4.13
In the industrial synthesis of acetic acid, methanol is treated with carbon monoxide. How many moles of CO are required to produce 16.6 mol of acetic acid?

[latex]\underset{\substack{ ext{Methanol}}}{ ext{CH}_{3} ext{OH}(\ell)} + \underset{\substack{ ext{Carbon}\ ext{monoxide}}} { ext{CO(g)}} \longrightarrow \underset{\substack{ ext{Acetic acid}}}{ ext{CH}_{3} ext{COOH}(\ell)}[/latex]

Question 4.13: Stoichiometry Silicon to be used in computer chips is manufa...

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