Question

A chemist removes 750 muL of a 4.44 x 10-3 M Na2S solution. How many moles of Na+ ions are present in the aliquot

Answer 1

An ‘aliquot’ in chemistry means a portion of the larger whole i.e. the stock solution assumed to be taken with minimum sampling error. So, here, the aliquot is ‘750 µL of 4.44 × 10^-3 M Na₂S solution’. Now we can see that

            1 mole of Na₂S solution contains 2 moles of Na⁺ ions.

            So, the ‘x’ number of moles of solute in the aliquot will contain ‘2x’ number of moles of Na⁺ ions.

Molarity of a solution is given by the formula:

So, the aliquot contains 3.33×10^-6 moles of solute i.e. Na₂S.

Therefore, 3.33×10^-6 moles of Na₂S (in the aliquot) contains = 2 × 3.33×10^-6 moles of Na⁺ ions

= 6.66×10^-6 moles of Na⁺ ions.