You dissolve 20.3 g of sodium chloride in 500 mL of water, what is the molarity of sodium cations in the solution as moles per litre?

The molarity of a solution is defined as the number of moles of solute (in this case, sodium chloride, NaCl) divided by the volume of the solution (in liters).

Here are the steps to calculate the molarity:

1. Calculate the number of moles of sodium chloride. The molar mass of sodium chloride is approximately 58.44 g/mol. So, the number of moles of sodium chloride is 20.3 g / 58.44 g/mol = 0.347 moles.

2. Convert the volume of the solution from milliliters to liters. 500 mL = 0.5 L.

3. Calculate the molarity of the sodium chloride solution. Molarity = moles of solute / volume of solution in liters = 0.347 moles / 0.5 L = 0.694 M.

4. However, each unit of NaCl dissociates into one Na+ ion and one Cl- ion in solution. Therefore, the molarity of Na+ ions is the same as the molarity of the NaCl solution.

So, the molarity of sodium cations in the solution is 0.694 M.