Question

A chemist wants to make 750mL of a 6M NaOH solution. What mass (in grams) of NaOH will they need?

Answer 1

180 g NaOH

Step-by-step explanation:

Step #1 : Use the molarity equation to find moles. The volume is needed in liters, so convert the milliliters to liters.

Molarity (M) = moles (mol) / liters (L) ---->

Molarity (M) x liters (L) = moles (mol)

750 mL NaOH 1 L
x ---------------- = 0.75 L NaOH
1,000 mL

(6 M NaOH) x (0.75 L NaOH) = ? mol

= 4.5 mol NaOH

Step #2 : Find the mass using the moles and the molar mass of the solution. The molar mass can be calculated using the values of the elements on the periodic table.

Molar Mass (g/mol) = grams (g) / moles (mol) --->

Molar Mass (g/mol) x moles (mol) = grams (g)

? g/mol = (22.99 g/mol Na) + (15.999 g/mol O) + (1.008 g/mol H)

? g/mol = 39.997 g/mol NaOH

(39.997 g/mol NaOH) x (4.5 mol NaOH) = ? g

= 179.99 g NaOH

= 180 g NaOH (2 sig figs)

= 200 g NaOH (1 sig fig)