1. Find the amount (i.e. number of moles) of sodium ions in 70.0mL of 3.0M sodium carbonate.
2. Find the amount of sodium ions in 30.0mL of 1.0M sodium bicarbonate.
Hint: Sodium carbonate = Na2CO3 and sodium bicarbonate = NaHCO3
3. Find the total volume when you mix the two solutions.
4. Add the results from (1) and (2) to find the total amount of sodium ions in your mixture.
5. Divide the moles of sodium ions (from 4) by the total volume (from 3) to find the concentration of sodium ions in your mixture.