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

Step-by-step explanation:

The given data is as follows.

Volume = 0.25 ml =
`0.25 * 0.001 L/ml` = 0.00025 l

mass =
`5.4 * 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 * 5.4 * 10^(-4) g/l`

=
`0.00135 * 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}}`

=
`(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.

Answer 2

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