Barrons SAT Subject Test Chemistry, 13th Edition

Solving for number of moles gives:

No. of moles of solute = M × volume in liters of solution

No. of moles of NaOH = 1.50 M × volume in liters of solution

The molar mass of NaOH = 23 + 16 + 1.0 = 40 g of NaOH

3. MOLALITY (abbreviated m) is defined as the number of moles of the solute
   dissolved in 1,000 grams of solvent.

Example

A 1 molal solution of H 2 SO 4 has 98 grams of H 2 SO 4 dissolved in 1,000. grams of

water. This, you will notice, gives a total volume greater than 1 liter, whereas the
molar solution had 98 grams in 1 liter of solution.

Example

Suppose that 0.25 mole of sugar is dissolved in 500. grams of water. What is the
molality of this solution?

If 0.25 mole is in 500. grams of H 2 O, then 0.50 mole is in 1,000 grams of H 2 O.

Thus:

m = 0.50

TIP

Know how to determine the mole fraction.

4. MOLE FRACTION is another way of indicating the concentration of a