Suppose 12.0 g of silicon (Si) reacts with 70.0 g of oxygen (O2) to give 25.6 g of the compou

step 1 We are asked to consider 12 grams, actually 12 .0 grams of silicon, reacts with 70 .0 grams of o

Suppose 12.0 g of silicon (Si) reacts with 70.0 g of...

Suppose $12.0 \mathrm{~g}$ of silicon (Si) reacts with $70.0 \mathrm{~g}$ of oxygen $\left(\mathrm{O}_{2}\right)$ to give $25.6 \mathrm{~g}$ of the compound silicon dioxide $\left(\mathrm{SiO}_{2}\right)$. In the process, all the silicon gets used up, but some oxygen is left over. (a) For the law of conservation of matter to be obeyed, how much oxygen is unused? (b) What is the percent $\mathrm{Si}$ in $\mathrm{SiO}_{2}$ ? (c) What is the percent $\mathrm{O}$ in $\mathrm{SiO}_{2}$ ?

Suppose $12.0 \mathrm{~g}$ of silicon (Si) reacts with $70.0 \mathrm{~g}$ of oxygen $\left(\mathrm{O}_{2}\right)$ to give $25.6 \mathrm{~g}$ of the compound silicon dioxide $\left(\mathrm{SiO}_{2}\right)$. In the process, all the silicon gets used up, but some oxygen is left over.
(a) For the law of conservation of matter to be obeyed, how much oxygen is unused?
(b) What is the percent $\mathrm{Si}$ in $\mathrm{SiO}_{2}$ ?
(c) What is the percent $\mathrm{O}$ in $\mathrm{SiO}_{2}$ ?

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Key Concepts

Percent Composition

Percent composition is the calculation of the mass percentage of each element within a compound. This concept is used to determine the proportion of each element in the compound, which is essential for both analyzing the makeup of compounds and for verifying reaction outcomes.

Stoichiometry

Stoichiometry involves the quantitative relationships between the amounts of reactants and products in a chemical reaction. It uses balanced chemical equations to relate masses, moles, or volumes, allowing us to determine how much of each substance participates or is produced in the reaction.

Limiting Reactant and Excess Reactant

The limiting reactant in a chemical reaction is the substance that is completely consumed first, determining the maximum amount of product that can be formed. In contrast, an excess reactant is present in a greater amount than needed and will not be entirely consumed, which is useful for calculating the mass of reactants remaining after the reaction.

Law of Conservation of Mass

This fundamental principle states that in any closed system, the total mass of the reactants is equal to the total mass of the products. No mass is lost or gained during a chemical reaction, which allows for the calculation of unused reactants when one or more reactants do not completely convert to the product.

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