Question

A 8.20 g sample of an aqueous solution of perchloric acid contains an unknown amount of the acid. If 20.4 mL of 0.922 M potassium hydroxide are required to neutralize the perchloric acid, what is the percent by mass of perchloric acid in the mixture?

Answer 1

Answer: The percent by mass of perchloric acid in the mixture is 22.92 %.

Step-by-step explanation:

• To calculate the moles of a solute, we use the equation:

`\text{Molarity of the solution}=\frac{\text{Moles of solute}}{\text{Volume of solution (in L)}}`

We are given:

Volume of potassium hydroxide = 20.4mL = 0.0204 L (Conversion factor: 1 L = 1000 mL)

Molarity of the solution = 0.922 moles/ L

Putting values in above equation, we get:

`0.922mol/L=\frac{\text{Moles of potassium hydroxide}}{0.0204L}\\\\\text{Moles of potassium hydroxide}=0.0188mol`

• For the given chemical reaction:

`HClO_4+KOH\rightarrow KClO_4+H_2O`

By Stoichiometry of the reaction:

1 mole of potassium hydroxide reacts with 1 mole of perchloric acid.

So, 0.0188 moles of potassium hydroxide will react with =
`(1)/(1)* 0.0188=0.0188mol` of perchloric acid.

• To calculate the mass of perchloric acid, we use the equation:

`\text{Number of moles}=\frac{\text{Given mass}}{\text{Molar mass}}`

Moles of perchloric acid = 0.0188 moles

Molar mass of perchloric acid = 100.46 g/mol

Putting values in above equation, we get:

`0.0188mol=\frac{\text{Mass of perchloric acid}}{100.46g/mol}\\\\\text{Mass of perchloric acid}=1.88g`

• To calculate the percent by mass of perchloric acid, we use the equation:

`\text{Mass percent}=\frac{\text{Mass of the solute}}{\text{Mass of solution}}* 100`

We are given:

Mass of perchloric acid = 1.88 g

Mass of solution = 8.20 g

Putting values in above equation, we get:

`\text{Mass percent of perchloric acid}=(1.88g)/(8.20g)* 100\\\\\text{Mass percent of perchloric acid}=22.92\%`

Hence, the percent by mass of perchloric acid in the mixture is 22.92 %.