Question

Calculate the molarity of each of the following solutions. (mol/L)

(a) 6.19 g of methanol (CH3OH) in 1.50 × 102 mL of solution:

______mol/L

(b) 9.43 g of calcium chloride (CaCl2) in 2.20 × 102 mL of solution:

______mol/L

(c) 8.86 g of naphthalene (C10H8) in 85.2 mL of benzene solution:

_______mol/L

Answer 1

a) Molarity of methanol is 1.24 M or 0.19 moles/0.153 litres.

b) molarity of CaCl2 is 0.37 M or 0.084 moles/ 0.2244litres.

c) molarity of napthalene is 0.81 M or 0.069 moles/0.085 litres.

Explanation:

The formula used in the calculation of molarity is:

molarity = $\frac{number of moles}{volume}$     equation 1

number of moles can be calculated as:

number of moles = $\frac{mass}{atomic mass of one mole}$   equation 2

a) mass of methanol = 6.19 grams

   volume of the solution = 1.50 x 102 ml= 153 ml or 0.153 L

   atomic mass of methanol = 32.04 gram/mole

number of moles will be calculated by putting the given values in equation 2

number of moles = $\frac{6.19}{32.04}$

                             = 0.19 moles

molarity is known by putting the values in equation 1

molarity = $\frac{0.19}{153}$

             = 1.24 M

b) mass of CaCl2 = 9.43 gram

  volume of the solution= 224 ml or 0.2244 litres

atomic mass of CaCl2 = 110.8 gram/mole

number of moles is calculated using equation 2

number of moles = $\frac{9.43}{110.98}$

                             = 0.084 moles

molarity is calculated using equation 1

molarity = $\frac{0.084}{0.2244}$

              = 0.37 M

c) mass = 8.86 gram

  volume = 85.2 ml or 0.08512 L

  atomic mass = 128.17

number of moles is calculated by putting the values in equation2:

number of moles = $\frac{8.86}{128.17}$

                             = 0.069 moles

molarity = $\frac{0.069}{0.08512}$

              = 0.80 M