Question

When a concentrated stock solution is diluted to prepare a less concentrated reagent, the number of _____ is the same both before and after the dilution.

Short answer

When a concentrated stock solution is diluted to prepare a less concentrated reagent, the number of \(moles\) of solute is the same both before and after the dilution.

Step-by-step solution

Understand the concept of dilution

Dilution is the process of reducing the concentration of a solute in a solution by mixing it with more solvent (usually water). The amount of solute is the same before and after dilution, only the volume of the solution increases, causing a decrease in concentration.

Identify the constant property in dilution

In the dilution process, the amount of solute remains constant. In other words, the number of moles of the solute remains the same before and after dilution.

Apply the dilution formula

To help understand the constant property in dilution, the dilution formula is used: \( C_1V_1 = C_2V_2 \) Where \(C_1\) is the initial concentration, \(V_1\) is the initial volume, \(C_2\) is the final concentration, and \(V_2\) is the final volume. This equation tells us that the product of the initial concentration and volume is equal to the product of the final concentration and volume, which implies that the number of moles of solute remains constant during dilution.

Answer the question

When a concentrated stock solution is diluted to prepare a less concentrated reagent, the number of moles of solute is the same both before and after the dilution.

Key concepts

Dilution Formula

The dilution formula is a mathematical expression that helps you calculate the concentration of a solution after it has been diluted. It's based on the principle that when you add more solvent to a solution, the amount of dissolved substance (the solute) stays the same, only distributed within a larger volume. Here's the formula:
\[\begin{equation} C_1V_1 = C_2V_2 \tag{1} \end{equation}\]
In this equation, \(C_1\) represents the initial concentration of the solution, while \(V_1\) represents the initial volume. After dilution, \(C_2\) is the new concentration and \(V_2\) is the new volume. The concept might seem tricky at first, but with a little practice, you'll find it becomes quite straightforward. Think of it like this: if you have a strong cup of tea (\(C_1\)) in a small teapot (\(V_1\)), pouring it into a bigger pot (\(V_2\)) and adding more water won't change how much tea leaves you originally had, but it will make the tea weaker (\(C_2\)).

Concentration of Solutions

Understanding the concentration of solutions is crucial in fields like chemistry and biology. The concentration can be thought of as how 'strong' a solution is. In other words, it measures how much solute is present in a given volume of solvent. It's usually expressed in terms like molarity, which is moles of solute per liter of solution.
To get a clear picture, imagine having a glass of lemonade. The amount of lemon juice in the water would be the 'concentration' of your drink. If you add too much water, the drink becomes less 'concentrated' and tastes weaker. The same concept applies when you’re working in the lab. If you have a very concentrated acid, for instance, you might dilute it to a specific concentration to make it safer to handle or to use in experiments which require a less concentrated acid.

Moles of Solute

The term 'moles of solute' is a way to quantify the amount of a substance. A mole is a unit used in chemistry to express amounts of a chemical substance, defined as containing exactly 6.02214076×10²³ (Avogadro's number) of particles, be it atoms, molecules, ions, or electrons.
When you dissolve a substance in a solvent to make a solution, the number of moles of that substance is what determines the solution’s concentration. This concept is vital for the dilution process. No matter how much you dilute a solution, the moles of solute do not change; they just become more spread out. To circle back to our lemonade example: If you start with a certain number of lemon juice molecules in a glass, adding more water doesn't make those molecules disappear – there are still the same number of molecules, just in a larger volume. Remembering that the moles of solute remain constant before and after dilution will help you better understand the process and use the dilution formula correctly.