Question

If you want to double the concentration of a solution, how could you do it? [Section 4.5]

Short answer

To double the concentration of a solution, you can either increase the mass of the solute by carefully weighing and adding more solute to the existing solution, or decrease the volume of the solution to half by evaporating or removing half of the solvent, such as heating an aqueous solution to evaporate the water.

Step-by-step solution

Method 1: Increasing the mass of solute

Adding more solute to the solution increases the mass of the solute, resulting in an increase in the concentration. To double the concentration, we need to double the mass of solute dissolved in the solution, while keeping the volume of the solution constant. This can be done by carefully weighing the solute and adding it to the existing solution, stirring it until it dissolves completely.

Method 2: Decreasing the volume of the solution

Another way to double the concentration is to decrease the volume of the solution to half without changing the mass of the solute. This can be done by evaporating or removing half of the solvent from the solution. For instance, if the solution is aqueous, we can heat the solution to evaporate the water until the volume of the solution is reduced by half. Once the volume is half of the initial volume, the concentration of the solution will be doubled.

Key concepts

Concentration of Solution

Understanding the concentration of a solution is essential for various scientific fields, including chemistry and biology. Concentration refers to the amount of solute that is dissolved in a given amount of solvent. It’s often expressed in terms of mass per unit volume, such as grams per liter (g/L). To visualize it simply, imagine you have a glass of lemonade—the amount of lemon and sugar mixed into the water determines how concentrated your drink is.

If a student wishes to double the concentration of a solution, they fundamentally need to alter the solute-to-solvent ratio. This could mean either adding more solute—the substance being dissolved—or reducing the amount of solvent, which is the substance doing the dissolving, typically a liquid like water. In our lemonade example, doubling the concentration could mean adding more lemon and sugar without adding more water, or it could mean letting some water evaporate off.

Mass of Solute

The mass of solute is simply how much of the substance is being dissolved into the solvent. This is commonly measured in units of mass such as grams or kilograms. When you’re aiming to double the concentration of a solution, one approach is to add more solite to the existing solution. This is akin to boosting the flavor of your drink by adding more lemon and sugar: you intensify the taste without increasing the amount of water in the glass.

In a laboratory setting, solutes are usually added using precise measurements to ensure the correct concentration is achieved. For the student's exercise, doubling the solute means measuring an equivalent amount that is already present in the solution and adding it in. Keep in mind it's crucial to ensure that the added solute is fully dissolved, otherwise, the actual concentration may differ from the calculated one.

Volume of Solution

The volume of the solution is the total space that the mixture of solute and solvent occupies, typically measured in liters (L) or milliliters (mL). Since concentration is tied to the volume, reducing the solution’s volume is another effective method to double its concentration. Imagine our lemonade glass is full: if we pour out half of it, the remaining lemonade is more intense in flavor because the same amount of sugar and lemon is now in less water.

In the context of the problem at hand, if a student reduces the solution's volume by half while keeping the mass of the solute constant, they effectively double the solution's concentration. It is essential, however, that this reduction is done carefully to avoid spilling or losing solute in the process, as this would alter the final concentration.

Solvent Evaporation

Solvent evaporation is a process where the solvent turns from a liquid into a gas and leaves the solution, typically under the influence of heat. In the classroom or laboratory, this can be achieved by heating the solution gently until the desired amount of solvent has evaporated. This method is particularly handy if adding more solute is impractical due to solubility limits or if precision in measurement must be attained without altering the solute amount.

A practical tip for students conducting evaporation is to control the heat source to avoid rapid boiling, which might lead to loss of solute through splattering or decomposition. Monitoring the volume throughout the process ensures that exactly half of the solvent is removed to achieve the objective of doubling the solution's concentration. Evaporation is quite common in everyday life, too—for instance, when a puddle dries up after a sunny day, that's solvent evaporation in action.