You dissolve 21.59 g of sodium chloride in 500 mL of water, what is the molarity of sodium cations in the solution as moles per litre?

Molarity is defined as the number of moles of solute per liter of solution.

Given: Mass of NaCl = 21.59 g Volume of water = 500 mL = 0.5 L (since 1 L = 1000 mL) Molar mass of NaCl = 58.44 g/mol

Step 1: Calculate the number of moles of NaCl:

Number of moles = mass of substance (in grams) / molar mass (in g/mol) Number of moles = 21.59 g / 58.44 g/mol = 0.370 moles

Step 2: Calculate the molarity of the solution:

Molarity = number of moles / volume of solution (in L) Molarity = 0.370 moles / 0.5 L = 0.740 M

However, each molecule of NaCl dissociates into one Na+ ion and one Cl- ion. 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 0.740 M.