Question

How many moles of sodium chloride (NaCl) solute are in 155 grams of an 85.5 percent by mass solution?

Answer 1

Our solution has 85.5 g of solute in 100 g of solution:


`155\ g\ solution\cdot (85.5\ g\ NaCl)/(100\ g\ solution) = 132.52\ g\ NaCl`

The molecular mass of NaCl is: 23 + 35.5 = 58.5 g/mol.


`132.52\ g\ NaCl\cdot (1\ mol)/(58.5\ g) = \bf 2.26\ mol\ NaCl`

Answer 2

85.5 percent by mass = 85.5 / 100 = 0.855

155 g x 0.855 => 132.525 g ( mass of solute )

Molar mass NaCl = 58.44 g/mol

number of moles:

n = mass of solute / molar mass

n = 132.525 / 58.44

n = 2.27 moles of NaCl

hope this helps!