Question

How do we define the mass percent composition of a solution? Give an example of a solution, and explain the relative amounts of solute and solvent present in the solution in terms of the mass percent composition.

Short answer

The mass percent composition of a solution is calculated by dividing the mass of a component (solute or solvent) by the total mass of the solution and then multiplying by 100. For example, in a solution prepared by dissolving 10 grams of salt in 90 grams of water, the mass percent composition of salt (solute) would be \(\frac{10\ grams}{(10+90)\ grams} \times 100 = 10\%\), and for water (solvent), it would be \(\frac{90\ grams}{(10+90)\ grams} \times 100 = 90\%\). This indicates that 10% of the total mass is salt, and the remaining 90% is water.

Step-by-step solution

1. Define Mass Percent Composition

Mass percent composition, also known as weight/weight percentage (w/w%), is a way to express the concentration of a component in a mixture or solution by calculating the mass of the component divided by the total mass of the mixture or solution and then multiplying by 100 to obtain the percentage value.

2. Formula for Mass Percent Composition

The formula for calculating mass percent composition of a component (solute or solvent) in a solution can be written as: \[mass\ percent\ composition\ (\%) = \frac{mass\ of\ component}{total\ mass\ of\ solution} \times 100\]

3. Example: Salt dissolved in water

For example, consider a solution prepared by dissolving 10 grams of table salt (sodium chloride, NaCl) into 90 grams of water (H₂O). We can find the mass percent composition of both the solute and solvent in this solution.

4. Calculate Mass Percent Composition for Salt (Solute)

We can use the formula to find the mass percent composition of salt (NaCl) in the solution: \[mass\ percent\ of\ NaCl\ (\%) = \frac{mass\ of\ NaCl}{total\ mass\ of\ solution} \times 100\] Plugging the values: \[mass\ percent\ of\ NaCl\ (\%) = \frac{10\ grams}{(10+90)\ grams} \times 100 = \frac{10}{100} \times 100 = 10\%\]

5. Calculate Mass Percent Composition for Water (Solvent)

Now, we can calculate the mass percent composition of water (H₂O) in the solution using the same formula: \[mass\ percent\ of\ H₂O\ (\%) = \frac{mass\ of\ H₂O}{total\ mass\ of\ solution} \times 100\] Plugging the values: \[mass\ percent\ of\ H₂O\ (\%) = \frac{90\ grams}{(10+90)\ grams} \times 100 = \frac{90}{100} \times 100 = 90\%\]

6. Interpret the Results

Based on the calculation, the mass percent composition of the solution is 10% for the solute (salt) and 90% for the solvent (water). This means that in this solution, 10% of the total mass is made up of salt, while the remaining 90% is made up of water.

Key concepts

Solution Concentration

Solution concentration is a measure that describes how much of a particular substance, known as the solute, is present in a solution in relation to the total amount of solution. Concentration can be expressed in different units, such as molarity, molality, or mass percent composition. Among these, mass percent composition is a common way to convey how concentrated a component is within a solution. By understanding solution concentration, we can determine the proportions of substances within mixtures, which is crucial for applications ranging from industrial processes to everyday cooking.
Some ways concentration is useful include:

• Ensuring the right ratio of ingredients in chemical reactions.
• Controlling the strength of solutions in pharmaceuticals.
• Maintaining proper flavor balance in culinary recipes.

Component Mass Calculation

To calculate the mass percent composition of a solution, you first need to know the mass of each component within the solution—the solute and the solvent. The component of interest, either solute or solvent, is divided by the total mass of the solution, and then multiplied by 100 to express it as a percentage. This formula gives you a straightforward way to calculate concentration based on mass:\[mass\ percent\ comp.\ (\%) = \frac{mass\ of\ component}{total\ mass\ of\ solution} \times 100\]This calculation is vital in various fields like chemistry and biology because it allows scientists and technicians to adjust or verify the concentrations of solutions they work with. Mass percent provides a clear picture of how much of a substance is present relative to the entire solution, which is particularly valuable when precise concentrations are necessary.

• Measure the mass of the solute and the solvent separately.
• Add these masses together to get the total mass of the solution.
• Apply the formula to determine the mass percent of each component.

Table Salt Example

Let's take table salt (sodium chloride, NaCl) as an example to better understand mass percent composition. Suppose you dissolve 10 grams of salt in 90 grams of water, creating a simple solution. Here, salt is the solute and water is the solvent. The total mass of the solution becomes 100 grams (10 grams NaCl + 90 grams H₂O).
By using the formula for mass percent composition, you can calculate:

• The mass percent of salt (solute): \[\frac{10\ grams}{100\ grams} \times 100 = 10\%\]
• The mass percent of water (solvent): \[\frac{90\ grams}{100\ grams} \times 100 = 90\%\]

This example shows that in this solution, 10% of the total mass is comprised of salt, while the remaining 90% is water. Understanding such solutions in real-world applications can assist in predicting their behavior, reactivity, and use in various settings.

Solute and Solvent

In the context of solutions, the solute and solvent are key components that define the entire makeup of the mixture. The solute is the substance that gets dissolved—it's typically present in a smaller amount—while the solvent is the component in which the solute is dissolved, often present in a greater amount. Together, they form a homogenous mixture known as a solution.
A solution can have varying solute and solvent identities:

• Solute: Could be a solid, liquid, or gas.
• Solvent: Often a liquid, but can also be a solid or gas.

When computing mass percent compositions, distinguishing between solute and solvent is crucial because it outlines the role each plays within the solution. The solute contributes to the characteristics of the solution such as taste, color, and chemical properties, while the solvent generally determines the phase of the solution and often remains consistent across different solutions. This understanding is important for practical application in science, medicine, and industry.