Problem 49 - Chemistry Matter and Change

Question

Solid silicon dioxide, often called silica, reacts with hydrofluoric acid (HF) solution to produce the gas silicon tetrafluoride and water. a. Write the balanced chemical equation for the reaction. b. List three mole ratios, and explain how you would use them in stoichiometric calculations.

Step-by-Step Solution

Answer

The balanced chemical equation for the reaction of solid silicon dioxide with hydrofluoric acid is: SiO₂(s) + 4HF(aq) → SiF₄(g) + 2H₂O(l) Three mole ratios derived from the balanced equation are: 1. Mole ratio of SiO₂ to HF: \( \frac{1 \text{ mole SiO}₂}{4 \text{ moles HF}} \) 2. Mole ratio of SiO₂ to SiF₄: \( \frac{1 \text{ mole SiO}₂}{1 \text{ mole SiF}₄} \) 3. Mole ratio of SiO₂ to H₂O: \( \frac{1 \text{ mole SiO}₂}{2 \text{ moles H}₂\text{O}} \) These mole ratios can be used in stoichiometric calculations to convert moles of one substance to moles of another substance, determine limiting reactants, excess reactants, or percentage yield in a chemical reaction.

Step 1: Write the balanced chemical equation for the reaction.

First, we need to write the unbalanced chemical equation using the chemical formulas of the reactants and products. Silicon dioxide (SiO₂) + Hydrofluoric acid (HF) → Silicon tetrafluoride (SiF₄) + Water (H₂O) Now, balance the chemical equation by adjusting the coefficients. SiO₂ + 4HF → SiF₄ + 2H₂O So, the balanced chemical equation is: SiO₂(s) + 4HF(aq) → SiF₄(g) + 2H₂O(l)

Step 2: List three mole ratios.

Mole ratios are derived from the balanced chemical equation. They represent the relationship between the moles of reactants and products. In this case, we can determine the following three mole ratios: 1. Moles of SiO₂ to moles of HF 2. Moles of SiO₂ to moles of SiF₄ 3. Moles of SiO₂ to moles of H₂O The mole ratios are calculated from the coefficients of the balanced equation: 1. Mole ratio of SiO₂ to HF: \( \frac{1 \text{ mole SiO}₂}{4 \text{ moles HF}} \) 2. Mole ratio of SiO₂ to SiF₄: \( \frac{1 \text{ mole SiO}₂}{1 \text{ mole SiF}₄} \) 3. Mole ratio of SiO₂ to H₂O: \( \frac{1 \text{ mole SiO}₂}{2 \text{ moles H}₂\text{O}} \)

Step 3: Explain how to use mole ratios in stoichiometric calculations.

Mole ratios are used to convert moles of one substance to moles of another substance in a balanced chemical equation. They can be used to determine the amount of reactants or products in a chemical reaction using stoichiometry. For example, if you are given the moles of SiO₂ and want to determine the moles of HF required for the reaction, you can use the mole ratio of SiO₂ to HF: Moles of HF = (Moles of SiO₂) × \( \frac{4 \text{ moles HF}}{1 \text{ mole SiO}₂} \) Similarly, if you want to find the moles of SiF₄ produced from a given amount of SiO₂, you can use the mole ratio of SiO₂ to SiF₄: Moles of SiF₄ = (Moles of SiO₂) × \( \frac{1 \text{ mole SiF}₄}{1 \text{ mole SiO}₂} \) Lastly, to find the moles of H₂O produced from a given amount of SiO₂, you can use the mole ratio of SiO₂ to H₂O: Moles of H₂O = (Moles of SiO₂) × \( \frac{2 \text{ moles H}₂\text{O}}{1 \text{ mole SiO}₂} \) These mole ratios can also be used to solve more complex stoichiometry problems, like finding the limiting reactant, the amount of excess reactant, or the percentage yield of a reaction.

Key Concepts

Chemical Reactions

In the world of chemistry, a chemical reaction takes place when substances react to form new products. This process involves the breaking and forming of chemical bonds. In our everyday lives, chemical reactions are all around us. They occur when we cook food, digest meals, or even breathe air. For example, when solid silicon dioxide (SiO₂) reacts with hydrofluoric acid (HF), a chemical reaction occurs, resulting in the formation of silicon tetrafluoride (SiF₄) and water (H₂O).
It’s important to understand that during a chemical reaction, the atoms themselves are not destroyed but merely rearranged, creating new products while conserving mass. This is where stoichiometry comes into play, helping us quantify and predict these re-arrangements through calculations. By understanding the nature of chemical reactions, we can better predict the outcome and necessary quantities of products and reactants in any given situation.

Balanced Chemical Equation

A balanced chemical equation represents a chemical reaction in which the number of atoms for each element is equal on both sides of the equation. This ensures that mass is conserved during the reaction, following the Law of Conservation of Mass.
When we look at the reaction between SiO₂ and HF, the unbalanced equation is:

• SiO₂ + HF → SiF₄ + H₂O

To balance this, we adjust the coefficients (the numbers in front of molecules) so that the number of each type of atom is the same on both sides. The balanced equation becomes:

• SiO₂ + 4HF → SiF₄ + 2H₂O

This equation tells us that one molecule of SiO₂ reacts with four molecules of HF to produce one molecule of SiF₄ and two molecules of H₂O. Balancing chemical equations is crucial for accurately determining the relationships and mole ratios between the reactants and products.

Mole Ratios

Mole ratios are derived from the coefficients of a balanced chemical equation and represent the proportional relationship between the amount in moles of reactants and products. These ratios are an essential part of stoichiometric calculations because they allow for the translation of quantities of one substance to another.
Taking the balanced chemical equation for the reaction of silicon dioxide with hydrofluoric acid, we identify three important mole ratios:

• Mole ratio of SiO₂ to HF: \( \frac{1 \, \text{mole SiO₂}}{4 \, \text{moles HF}} \)
• Mole ratio of SiO₂ to SiF₄: \( \frac{1 \, \text{mole SiO₂}}{1 \, \text{mole SiF₄}} \)
• Mole ratio of SiO₂ to H₂O: \( \frac{1 \, \text{mole SiO₂}}{2 \, \text{moles H₂O}} \)

Mole ratios are used to convert the amount of one substance (given in moles) to the amount of another substance in the reaction. For example, if we have a certain amount of SiO₂ and want to find out how much HF is needed, we simply multiply the moles of SiO₂ by the mole ratio of HF. This is done by using the conversion factor from the ratio, ensuring accurate stoichiometric calculations that are vital in both laboratory and industrial chemical processes.