Question

A laboratory assistant prepared a potassium chloride solution for her class by dissolving \(5.34 \mathrm{g}\) of \(\mathrm{KCl}\) in 152 g of water. What is the mass percent of the solution she prepared?

Short answer

The mass percent of the potassium chloride solution prepared by the laboratory assistant is approximately \(3.39\%\).

Step-by-step solution

Calculate the total mass of the solution

First, we need to find the total mass of the solution. This can be done by adding the mass of the solute (KCl) and the mass of the solvent (water) together. Total mass of solution = Mass of KCl + Mass of water Total mass of solution = 5.34 g + 152 g Total mass of solution = 157.34 g

Calculate the mass percent of KCl in the solution

Now, we will find the mass percent of potassium chloride in the solution using the formula mentioned in the analysis: Mass percent = (Mass of solute / Total mass of solution) × 100 Mass percent = (Mass of KCl / Total mass of solution) × 100 Plug in the values we found in Step 1: Mass percent = (5.34 g / 157.34 g) × 100

Express the final result as a percentage

Finally, complete the calculation to get the mass percent of KCl as a percentage: Mass percent = (5.34 g / 157.34 g) × 100 ≈ 3.39 % The mass percent of the potassium chloride solution prepared by the laboratory assistant is approximately 3.39%.

Key concepts

Potassium Chloride Solution

When discussing a potassium chloride solution, we're talking about a mixture that involves dissolving potassium chloride (KCl) in water. This solution is frequently used in chemistry labs because KCl is a common salt that helps illustrate how solutes dissolve in a solvent.

• Potassium chloride is made up of potassium (K) and chloride (Cl) ions.
• In water, these ions dissociate, making the solution electrically conductive.

The concentration of the solution can be expressed in different ways, one of which is mass percent, which tells us how much solute is present compared to the entire solution.

Solute and Solvent

In any solution, there are two main components: the solute and the solvent. Understanding these components is crucial for solving problems involving solutions.

• The solute is the substance that gets dissolved. In our example, potassium chloride is the solute.
• The solvent is the substance that does the dissolving. For our potassium chloride solution, water acts as the solvent.
• A solution forms when the solute mixes uniformly with the solvent.

Mass percent calculation, such as described in the exercise, uses these concepts by measuring how much solute is dissolved compared to the total solution mass.

Total Mass of Solution

To find the mass percent of a solution, we first need to determine the total mass of the solution. This step is essential because it combines both the solute and the solvent.

• In our example, the total mass of the solution is the sum of KCl's mass and the mass of water.
• The calculation goes: \(5.34\, \text{g} + 152\, \text{g} = 157.34\, \text{g}\).

By knowing the total mass, you can further calculate how much of that mass is percent-wise made up of potassium chloride through mass percent calculations.

Stoichiometry in Chemistry

Stoichiometry is the part of chemistry that deals with the calculation of reactants and products in chemical reactions. While the term often applies to chemical reactions, its principles can help us understand solution concentrations too.

• It involves using balanced equations to calculate quantities like mass, volume, and number of molecules.
• Here, stoichiometry helps to ensure the proper ratio between solute and solvent is maintained.

When calculating the mass percent of a substance like potassium chloride in a solution, we're essentially using stoichiometric concepts to express how much of the solute (KCl) is present per 100 parts of the total solution.