Question

How do you calculate the number of sodium ions, `Na^+`, in 14.2 g of sodium sulfate? [Relative atomic masses Na = 23, S = 32, O = 16]?

Answer 1

Use the number of moles of sodium per mole of sodium sulfate.

Explanation:

Sodium sulfate is `Na_2` `SO_4`
First, calculate the moles of sodium sulfate you have in a 14.2g sample.

1. Find the molar mass of sodium sulfate
   molar mass = atomic mass in grams
   2(23) + 32 + 4(16) = 142 grams per mole
2. Divide the mass of the sample by the molar mass to obtain moles
   `(14.2g)/(142gmol^-1)` = 0.1 mol

Now, for every 1 mol of `Na_2` `SO_4` you have 2 moles of `Na^+` ions. Multiple the moles of `Na_2` `SO_4` that you found just then by 2 to obtain the moles of sodium ions.

Use Avogadro's number (6.022 x `10^23`) to find the number of ions present. (Recall that Avogrado's number is the number of particles per mole of a substance).

6.022 x `10^23` x 0.2 mol = 1.2044 x `10^23` ions