212 g Na₂CO₃
We are given;
We are required to calculate the mass of Na₂CO₃.
We need to know how molarity is calculated.
Moles = Molarity × Volume
Therefore;
Moles of Na₂CO₃ = 4.00 M × 0.5 L
= 2 moles
Thus, moles of Na₂CO₃ is 2 moles
We need to know the relationship between the mass of a compound, molar mass and the number of moles.
Moles = Mass ÷ molar mass
Rearranging the formula;
Mass = Moles × molar mass
Molar mass of Na₂CO₃ is 106 g/mol
Therefore;
Mass of Na₂CO₃ = 2 moles × 106 g/mol
= 212 g
Therefore, the mass of Na₂CO₃ that would be needed is 212 g