Calculating Molarity of a NaOH Solution

To calculate the molarity of a NaOH solution, we need to know the weight of NaOH and the volume of the solution. In this case, we are given the weight of NaOH as 20% weight by weight and the density of the solution as 1.2 gm/cc.

Step 1: Convert Weight Percentage to Grams
First, we need to convert the weight percentage of NaOH to grams. Since the solution is 20% weight by weight, it means that 20 grams of NaOH is present in every 100 grams of the solution.

Step 2: Calculate the Weight of NaOH
To calculate the weight of NaOH, we can assume a convenient volume for the solution, such as 100 ml. Since the density of the solution is 1.2 gm/cc, the weight of the solution can be calculated as follows:
Weight of the solution = Volume of the solution x Density of the solution
Weight of the solution = 100 ml x 1.2 gm/cc = 120 grams

Therefore, the weight of NaOH in the solution is:
Weight of NaOH = Weight of the solution x Weight percentage of NaOH
Weight of NaOH = 120 grams x 20% = 24 grams

Step 3: Calculate the Molarity
To calculate the molarity, we need to know the molar mass of NaOH, which is 22.99 g/mol for Na, 16.00 g/mol for O, and 1.01 g/mol for H.

Molar mass of NaOH = 22.99 g/mol + 16.00 g/mol + 1.01 g/mol = 40.00 g/mol

Molarity (M) = Number of moles of solute / Volume of solution in liters
Number of moles of NaOH = Weight of NaOH / Molar mass of NaOH
Volume of solution = Weight of the solution / Density of the solution

Using the given values, we can calculate the molarity as follows:
Number of moles of NaOH = 24 grams / 40.00 g/mol = 0.6 moles
Volume of solution = 120 grams / 1.2 gm/cc = 100 ml / 1000 = 0.1 liters

Molarity (M) = 0.6 moles / 0.1 liters = 6 M

Therefore, the molarity of the NaOH solution is 6 M.