Question

The more reactive halogen elements are able to replace the less reactive halogens from their compounds. For example, if chlorine gas is bubbled through a potassium iodide solution, elemental iodine is produced. $$\mathrm{Cl}_{2}(g)+\mathrm{KI}(a q) \rightarrow \mathrm{I}_{2}(s)+\mathrm{KCl}(a q)$$ Calculate the mass of iodine produced when \(2.55 \mathrm{g}\) of chlorine gas is bubbled through an excess amount of potassium iodide solution.

Short answer

The mass of iodine produced when \(2.55 g\) of chlorine gas is bubbled through an excess amount of potassium iodide solution is \(9.14 g\).

Step-by-step solution

Write the balanced chemical equation

The balanced chemical equation for the reaction is already provided in the exercise: $$\mathrm{Cl}_{2}(g)+\mathrm{KI}(a q) \rightarrow \mathrm{I}_{2}(s)+\mathrm{KCl}(a q)$$

Convert mass of \(Cl_2\) to moles

To convert the mass of \(Cl_2\) to moles, we will use its molar mass. The molar mass of \(Cl_2\) is \(2 \times 35.45 = 70.90 \mathrm{g/mol}\). Then, to calculate the moles of \(Cl_2\), we will use the formula: \[\text{moles of } Cl_2 = \frac{\text{mass of } Cl_2}{\text{molar mass of } Cl_2}\] \[\text{moles of } Cl_2 = \frac{2.55 \,\text{g}}{70.90 \,\text{g/mol}} = 0.0360 \,\text{mol} \]

Calculate the moles of \(I_2\) produced

According to the stoichiometry of the balanced chemical equation, 1 mole of \(Cl_2\) reacts with 1 mole of \(KI\) to produce 1 mole of \(I_2\) and 1 mole of \(KCl\). So, the moles of \(I_2\) produced will be equal to the moles of \(Cl_2\). \[\text{moles of } I_2 = \text{moles of } Cl_2 = 0.0360 \,\text{mol}\]

Convert moles of \(I_2\) to mass

To convert the moles of \(I_2\) to mass, we will use its molar mass. The molar mass of \(I_2\) is \(2 \times 126.90 = 253.80 \mathrm{g/mol}\). Then, to calculate the mass of \(I_2\), we will use the formula: \[\text{mass of } I_2 = \text{moles of } I_2 \times \text{molar mass of } I_2\] \[\text{mass of } I_2 = 0.0360 \,\text{mol} \times 253.80 \,\text{g/mol} = 9.14 \,\text{g}\] So, the mass of iodine produced when \(2.55 g\) of chlorine gas is bubbled through an excess amount of potassium iodide solution is \(9.14 g\).

Key concepts

Reactive Halogens

In chemistry, halogens are a group of elements including fluorine, chlorine, bromine, iodine, and astatine. These elements are very reactive, especially with metals, because they need just one more electron to achieve a stable electron configuration. Within the group of halogens, reactivity decreases as you move down the periodic table. For example, chlorine is more reactive than iodine. This means chlorine can displace iodine in chemical reactions. This ability is demonstrated when chlorine gas is bubbled through a potassium iodide solution, generating elemental iodine. This is a classic example of a halogen displacement reaction.
Understanding the reactivity of halogens is crucial in predicting the outcomes of chemical reactions. The more reactive halogen will always replace the less reactive one in compounds.

Chemical Reactions

Chemical reactions are processes where substances, known as reactants, are transformed into different substances called products. This transformation occurs through the making and breaking of chemical bonds. In a chemical reaction like the one between chlorine gas and potassium iodide, chlorine, being the more reactive halogen, displaces iodine from potassium iodide.
This specific reaction showcases the dynamic nature of chemical changes:

• Reactants: Chlorine (\( \text{Cl}_2 \)) gas and potassium iodide (\( \text{KI} \)).
• Products: Iodine (\( \text{I}_2 \)) and potassium chloride (\( \text{KCl} \)).

Chemical reactions involve rearrangements of atoms and shifts in chemical identities, highlighting the importance of understanding their fundamental principles.

Stoichiometry

Stoichiometry is a key concept in chemistry that involves the calculation of reactants and products in chemical reactions. It is based on the conservation of mass, where the mass of reactants equals the mass of products. In the given reaction between \( \text{Cl}_2 \) and \( \text{KI} \), stoichiometry helps us understand the relationship between the amounts of reactants used and products formed.
Through stoichiometry:

• We can determine the amount of iodine produced from a given amount of chlorine.
• The mole ratio derived from the balanced equation shows that one mole of chlorine produces one mole of iodine, allowing us to calculate the exact mass of iodine formed in the reaction.

This systematic approach helps ensure precise predictions of product yields in chemical reactions.

Molar Mass

Molar mass is an essential concept for converting between grams and moles of a substance. It is the mass of one mole of a substance, usually measured in grams per mole (g/mol). Calculating molar mass involves adding up the atomic masses of elements present in a molecule.
In this example:

• The molar mass of \( \text{Cl}_2 \) is calculated as \( 2 \times 35.45 = 70.90 \text{ g/mol} \).
• Similarly, the molar mass of \( \text{I}_2 \) is \( 2 \times 126.90 = 253.80 \text{ g/mol} \).
• Using these values, we can convert masses to moles and vice versa, crucial for accurate stoichiometric calculations.

Thus, understanding molar mass is vital for predicting how much of each substance is needed or produced in a chemical reaction.

Balanced Chemical Equations

Balanced chemical equations are central to understanding chemical reactions. They represent the conservation of matter, ensuring that the same number of each type of atom appears on both sides of the equation. This is achieved by adjusting coefficients, not subscripts, in the chemical formulas.
In the \( \text{Cl}_2 + \text{KI} \to \text{I}_2 + \text{KCl} \) reaction:

• Each side of the equation contains the same number of chlorine, iodine, and potassium atoms, making it balanced.
• The balanced equation assures us that one mole of chlorine reacts with one mole of potassium iodide to produce one mole of iodine and one mole of potassium chloride.

Balanced equations are indispensable for performing accurate chemical calculations and ensuring predictions match actual experimental results.