Calculate the molarity of a solution containing 5 g of NaOH in 450 mL solution.

To calculate the molarity of a sodium hydroxide (NaOH) solution, you need to follow a few straightforward steps. Molarity (M) is defined as the number of moles of solute divided by the volume of the solution in liters. Let’s break it down step by step.

Step 1: Find the Molar Mass of NaOH

The first thing we need is the molar mass of sodium hydroxide (NaOH). This can be calculated by adding the atomic masses of its constituent elements:

• Sodium (Na): approximately 23.0 g/mol
• Oxygen (O): approximately 16.0 g/mol
• Hydrogen (H): approximately 1.0 g/mol

So, the molar mass of NaOH is:

23.0 + 16.0 + 1.0 = 40.0 g/mol

Step 2: Convert Grams to Moles

Now that we know the molar mass, we can convert the mass of NaOH in the solution from grams to moles. You have 5 g of NaOH. To find the number of moles, use the formula:

moles = mass (g) / molar mass (g/mol)

Substituting the values we have:

moles = 5 g / 40.0 g/mol = 0.125 moles

Step 3: Convert Volume from mL to Liters

The next step is to convert the volume of the solution from milliliters to liters, as molarity requires the volume to be in liters. Since there are 1000 mL in 1 L:

450 mL = 450 / 1000 = 0.450 L

Step 4: Calculate Molarity

Now we can calculate the molarity using the formula:

Molarity (M) = moles of solute / volume of solution in liters

Substituting the values we found:

M = 0.125 moles / 0.450 L

Calculating this gives:

M = 0.2778 M

Final Result

Therefore, the molarity of the sodium hydroxide solution is approximately 0.278 M. This means that in every liter of this solution, there are about 0.278 moles of NaOH dissolved. Understanding how to perform these calculations is crucial in chemistry, especially when preparing solutions for various experiments.