Calculate the sodium ion concentration when 70.0 mL of 3.0 M sodium carbonate is added to 30.0 mL of 1.0 M sodium
bicarbonate.

4.5 M Na+

Explanation:

Multiply the molarity by the volume of the solution to get moles.

Note that there are TWO sodium ions in sodium carbonate, therefore the first-mole calculation must be multiplied by two.

Since molarity is defined as moles of ions/liters of solution, the final molarity will be the sum of the calculated moles divided by the sum of the liters of solution.

Hope this helps :)