1. Determine the molar mass of sodium carbonate (Na₂CO₃):

* Na: 22.99 g/mol (x 2 since there are 2 sodium atoms) = 45.98 g/mol

* C: 12.01 g/mol

* O: 16.00 g/mol (x 3) = 48.00 g/mol

Total molar mass of Na₂CO₃ = 45.98 + 12.01 + 48.00 = 105.99 g/mol

2. Calculate the mass of sodium in 1 mole of Na₂CO₃:

* Mass of sodium in 1 mole of Na₂CO₃ = (45.98 g/mol Na) / (105.99 g/mol Na₂CO₃) = 0.434 g Na/g Na₂CO₃

3. Calculate the mass of sodium in 3 moles of Na₂CO₃:

* Mass of sodium in 3 moles of Na₂CO₃ = 0.434 g Na/g Na₂CO₃ x 3 moles Na₂CO₃ x 105.99 g Na₂CO₃/mol Na₂CO₃ = 138 g Na

Therefore, there are approximately 138 grams of sodium in 3 moles of sodium carbonate.