Question

What mass of KI is dissolved in \(700.0 \mathrm{~g}\) of a solution that is \(15.0 \%\) KI by mass?

Short answer

The mass of KI dissolved in the solution is 105.0g.

Step-by-step solution

Understanding Data

We have a total solution mass of 700.0g and a given KI concentration of 15.0%. We aim to find out how much KI this percentage corresponds to.

Rewrite the Formula

We know that the mass percent equation is: mass percent = (mass solute / mass solution) * 100. We can rewrite this equation to solve for mass solute: mass solute = (mass percent * mass solution) / 100.

Substitution

Substitute the given values: mass solute = (15.0 * 700.0) / 100.

Calculating

Perform the calculation to obtain the mass of KI.

Key concepts

Mass Percent Calculation

Mass percent is a simple way to express the concentration of a solute in a solution. It tells us how many grams of solute are present in 100 grams of solution. For example, if a solution is 15% potassium iodide (KI) by mass, this means there are 15 grams of KI in every 100 grams of the solution.

To find out how much KI is in a 700 g solution, we use the mass percent formula:

\[ \text{mass percent} = \left(\frac{\text{mass of solute}}{\text{mass of solution}}\right) \times 100 \]

By rearranging the formula to solve for the mass of the solute, we get:

\[ \text{mass of solute} = \left(\frac{\text{mass percent} \times \text{mass of solution}}{100}\right) \]

This rearrangement allows us to calculate the amount of KI using the given mass percent and the total mass of the solution.

Solute Concentration

Solute concentration refers to how much solute, like KI, is present in a solution. Understanding concentration is crucial for chemistry problems because it helps us understand how substances interact.

Concentration can be expressed in different ways:

• Mass percent: As used in this problem, it measures grams of solute per 100 grams of solution.
• Molarity: This considers moles of solute per liter of solution, different from mass percent.
• Molality: It calculates moles of solute per kilogram of solvent, providing another way to describe concentration.

For this exercise, focusing on mass percent allows us to directly calculate the mass of KI needed in the solution. By substituting the known values into our equation, we find that a 15% concentration in 700g equates to a certain mass of KI.

Solution Composition

When we talk about solution composition, we mean how a solution is made up of its different components, the solute and solvent.

In our example:

• Solute: KI (potassium iodide), the substance being dissolved.
• Solvent: The other substances in the solution, typically more abundant.

A solution's composition can significantly affect its properties and behavior in a chemical reaction. Knowing the specific amounts of solute and solvent helps determine reactions and outcomes.

For calculating purposes, understanding solution composition means being able to plug known values into an equation like the mass percent formula, which gives us an insightful understanding of what's in our solution. This composition is essential not just in textbooks, but also in real-world applications like cooking or formulating products.