Final answer:
To prepare a solution of NaNO₃ with a molarity of 0.138 M, you will need 0.374 g of NaNO₃.
Step-by-step explanation:
To find the mass of NaNO₃ required, we need to use the formula for molarity:
Moles of solute = Molarity × Volume of solution
First, convert the given volume of solution to liters:
31.8 mL ÷ 1000 = 0.0318 L
Next, plug in the values into the formula:
Moles of NaNO₃ = 0.138 M × 0.0318 L = 0.0044 mol
Finally, use the molar mass of NaNO₃ (85.0 g/mol) to calculate the mass:
Mass of NaNO₃ = 0.0044 mol × 85.0 g/mol = 0.374 g