Question

How many grams of NaOH were dissolved to make a 1.25 L solution of 2.92 M NaOH?

Answer 1

• 146. g

Step-by-step explanation:

1) Data:

a) mass of solute = ?

b) volume of solution = 1.25 liter

c) M = 2.92 mol/liter

d) solute NaOH

2) Formulae:

a) Molarity, M = number of moles of solute / volume of solution in liters

b) mass in grams = molar mass × number of moles

3) Solution:

a) Calculate number of moles of solute:

• M = number of moles of solute / volume of solution in liters

⇒ number of moles of solute = M × volume of solution in liters

⇒ number of moles of solute = 2.92 mol/liter × 1.25 liter = 3.65 mol

b) Molar mass of NaOH = 39.997 g/mol (you can take this number from internet or calculate it using the atomic masses of Na, O, and H).

c) Calculate the mass of solute:

• mass in grams = molar mass × number of moles = 39.997 g/mol × 3.65 mol = 145.98905 g = 146. g

The answer must be reported with 3 significant figures, so it is 146. g.