What is the mass in grams of na 2 co 3 (s) (molar mass = 105.98 g/mol) that, when dissolved in 125 ml of water, will make a 0.15 m aqueous solution?

Molarity is defined as the number of moles of solute dissolved in 1 L of solution.

molarity of sodium carbonate is 0.15 M

this means that 0.15 moles of sodium carbonate are dissolved in 1 L of solution

if 1 L contains - 0.15 mol

then 125 mL should contain - 0.15 mol/L x 0.125 L = 0.019 mol

mass of sodium carbonate in 125 mL - 0.019 mol x 105.98 g/mol = 2.0 g

2.0 g of sodium carbonate is required to make a 0.15 M solution