Question

How many SO32- ions are contained in 99.6 mg of Na2SO3? The molar mass of Na2SO3 is 126.05 g/mol.

Answer 1

Well, as you can see, it's a 2:1 ratio of ions here, you have 2 sodium ions per single sulfite ion.

So, you would start by firstly, converting \(\sf \color{red}{mg \rightarrow g}\) so you can use the given molar mass.

Your next step would be to convert: \(\sf \color{red}{g~Na_2SO_3 \rightarrow moles~of~ Na_2SO_3 \rightarrow moles~of~SO_3^{2-}}\)
that means grams of sodium sulfite to moles and then moles of sodium sulfite to moles of sulfite anion.

You'll then, finally, be applying, once you have moles, avogadro's constant, which is moles per unit, which you want, ions.

Avogadro's constant is: \(\sf \color{blue}{6.022 \times 10^{23} \large \frac{moles}{ion}}\)