Introduction:

In this problem, we are given the density of a solution of sodium chloride and we are asked to find its molarity.

Formula:

Molarity = moles of solute / liters of solution

Moles of solute = mass of solute / molar mass of solute

Calculation:

1. We know that the density of the solution is 1.21 g/ml. This means that 1 liter of the solution has a mass of 1210 g.

2. Let's assume we have x moles of sodium chloride dissolved in 1 liter of solution.

3. The mass of sodium chloride in 1 liter of solution would be x times its molar mass (58.44 g/mol). So, the mass of the solution would be:

1210 g = x * 58.44 g/mol

x = 20.7 moles

4. Now, we can use the formula for molarity to find its value:

Molarity = 20.7 moles / 1 liter

Molarity = 20.7 M

So, the molarity of the sodium chloride solution is 20.7 M.

Conclusion:

We have shown that the molarity of a sodium chloride solution with a density of 1.21 g/ml is 20.7 M. This involves using the formula for molarity and knowing the molar mass of sodium chloride.