Understanding Molarity Calculation: A Practical Example with NaOH

Molarity is a key concept in chemistry that helps us understand the concentration of solutions. This article will walk you through the step-by-step process of calculating the molarity of a sodium hydroxide (NaOH) solution. By the end, you will be able to apply these principles to similar problems.

What is Molarity?

Molarity is defined as the number of moles of solute per liter of solution. The formula to calculate molarity is:

Molarity (M) frac{text{moles of solute}}{text{liters of solution}}

The Step-by-Step Calculation

Let's work through a practical example step-by-step to understand how to calculate the molarity of a NaOH solution.

Step 1: Calculate the Moles of NaOH

The formula to find the molar mass of NaOH is:

Na: 22.99 g/mol O: 16.00 g/mol H: 1.01 g/mol

The molar mass of NaOH is:

Molar mass of NaOH 22.99 16.00 1.01 40.00, g/mol

Step 2: Find the Moles of NaOH

Given that the mass of NaOH is 40 g, we can calculate the moles of NaOH as follows:

Moles of NaOH frac{40, g}{40.00, g/mol} 1, mole

Step 3: Determine the Volume of the Solution

The solution is prepared by dissolving 40 g of NaOH in water to form 1 L of solution.

Step 4: Calculate the Molarity

Molarity is calculated using the formula:

Molarity frac{text{moles of solute}}{text{liters of solution}} frac{1, mole}{1, liter} 1, M

Therefore, the molarity of the solution is 1 M (molar).

Cross-Checking with Units

In any calculation, including the units is crucial to ensure that the calculation is correct. By checking the units, we can avoid simple arithmetic errors. For instance:

S frac{W}{MV} Where:

S Molarity (1 M) W Grams of solute (40 g) M Molar mass of solute (NaOH, 40 g/mol) V Volume of solution (1 L)

S frac{40, g}{40, g/mol times 1, L} 1, M

This confirms that the calculation is correct, as the units (mol/L) are consistent with the definition of molarity.

Conclusion

By understanding and applying the step-by-step process of calculating molarity, you can now confidently tackle similar problems involving different solutes and volumes. Remember, units are your friend in ensuring the accuracy of your calculations.