Question

How many moles of steric acid are contained in 0.25 ml of a hexane solution containing 5.4 x 10^-4 g stearic acid/l?

Answer 1

First, we determine the mass of stearic acid in the solution by multiplying the given concentration by the volume. 
                      mass of stearic acid = (5.4 x 10^-4 g/L) (0.25 mL) (1000 mL/1L)
                                                          = 0.135 g
Then, we divide this amount by the molar mass in order to obtain the number of moles of stearic acid. The molar mass of stearic acid is 284.4772 g/mol.
                   moles stearic acid = 0.135 g / (284.4772 g/mol)
                                                    = 4.75 x 10^-4 mol

Answer 2

Explanation:

The given data is as follows.

        Volume = 0.25 ml = $0.25 \times 0.001 L/ml$ = 0.00025 l

        mass = $5.4 \times 10^{-4} g/l$

Also, it is known that molar mass of stearic acid is 284.48 g/mol.

Therefore, calculate the mass present in 0.00025 l as follows.

          $0.00025 l \times 5.4 \times 10^{-4} g/l$

            = $0.00135 \times 10^{-4}$

            = 13.5 g

As number of moles is mass divided by molar mass of the substance. Hence, calculate the number of moles of stearic acid as follows.

                No. of moles = $\frac{mass}{\text{molar mass}}$

                                     = $\frac{13.5 g}{284.48 g/mol}$

                                     = 0.047 mol

Thus, we can conclude that there are 0.047 mol of steric acid are contained in the given solution.