Question

23.5 grams of sodium carbonate is dissolved in enough water to make 250 ml of solution.If sodium carbonate dissociates completely, molar concentration of sodium ion and carbonate ions are

Answer 1

Answer: The final concentrations are:

1.76 moles of sodium ions / one litre of solution

0.88 moles of carbonate ions / one litre of solution

Explanation:

1 - Count the molar mass of Na2CO3

23 *2 + 12 + 16*3 = 106

The molar mass of sodium carbonate is 106 grams per mole.

2 - Write the dissociation reaction

Na2CO3 --water---> 2 Na+ + CO3 2-

From this reaction we know that one mole of sodium carbonate dissociates into 2 moles of sodium ions and 1 mole of carbonate ions.

3 - Make a ratio

23.5/106 = 0.22

If 1 mole of Na2CO3 --------> 2 moles of sodium ions

                                    then

0.22 moles of Na2CO3 ---------- x moles of sodium ions

to find the x use the formula

0.22 x 2 / 1

therefore x=0.44 If you do the same with carbonate, you'll find that x for carbonate ions = 0.22

Now you know what the concetrations would be for one litre, so for 250ml you they'll be 4 times bigger:

0.44 x 4 = 1.76

0.22 x 4 = 0.88

So the final concentrations are:

1.76 moles of sodium ions / one litre of solution

0.88 moles of carbonate ions / one litre of solution