Understanding Molarity: How to Calculate Moles of a Solute in a Solution

What is Molarity?

Molarity (M) is a fundamental concept in chemistry that expresses the concentration of a solution. It is defined as:

$$Molarity(M)=\frac{\text{Moles of solute}}{\text{Liters of solution}}$$

This means that a 5.0 M solution contains 5.0 moles of solute per litre of solution.

How to Calculate the Number of Moles in a Solution

To determine the number of moles of solute present in a given volume of solution, use the formula:

$$\text{Moles of solute}=Molarity(M)\times Volume(L)$$

Example Calculation

Let's find out how many moles of glucose are present in 320 mL of a 5.0 M glucose solution.

Step 1: Convert volume from mL to L

$$320\times \frac{1\text{ L}}{1000\text{ mL}}=0.320\text{ L}$$

Step 2: Apply the formula

$$\text{Moles} = 5.0 \times 0.320$$
$$=1.6\text{ moles of glucose}$$

So, 1.6 moles of glucose are present in 320 mL of a 5.0 M solution.

Key Takeaways

• Molarity expresses the concentration of a solution in moles per litre.
• To find the number of moles in a given volume, multiply molarity by volume (in litres).
• Always convert mL to L before calculations.

Important Concept about Molarity Calculation

This simple formula helps in various chemistry applications, from lab experiments to industrial processes.