How do you calculate the number of ions in a solution?

Question

Natalie Anton · Accepted Answer

To determine the concentration of each ion, first determine the molar concentration and then consult the formula.

Lets look at an example: "How many sodium ions are there in a solution of sodium chloride of concentration #58.5 g.dm^(-3) ?# "

We need to convert this into #mol.dm^(-3)# . To do this we add up the #A_r# values to get the relative formula mass. For NaCl this will be 23 +35.5 = 58.5. So 1 mole of NaCl weighs 58.5g.

Thus, we must now divide the mass in grams by the mass of one mole in order to convert grams into moles.

Thus, 58.5/58.5 = 1 mole of NaCl is the number of moles.

So the concentration of NaCl is #1 mol.dm^(-3)#

This means that in #1dm^3# of solution there must be 1 mole of sodium ions.

The number of particles in 1 mole is given by the Avogadro Constant which is equal to #6.02x10^(23) mol^(-1)#. We usually give this the symbol L.

Thus, L sodium ions are present in the solution under consideration.

Check the stoichiometry of the formula. If you have #1dm^3# of a 1 molar solution of sodium sulfate #Na_2SO_4# then this would be 2 molar with respect to sodium ions so would contain 2L sodium ions.

Cooper Anderson · Answer

undefined To calculate the number of ions in a solution, you need to know the concentration of the ions in the solution and the volume of the solution. Multiply the concentration of the ion (in moles per liter) by the volume of the solution (in liters). This will give you the number of moles of ions. Then, multiply the number of moles by Avogadro's number (6.022 x 10^23 ions/mole) to find the number of ions in the solution.