Question

Perchloric acid is a strong acid with the chemical formula HCIO4. Youdissolved a certain amount of perchloric acid in 250mL of water. you measure thepH of the solution and obtain a pH of 1.28.a) Write the reaction of perchloric acid with water.b) What is the concentration of H3O+ ions in the acid solution?c) What mass of perchloric acid was used to prepare the solution?

Answer 1

`HClO_(4(s))+H_2O\rightarrow H_3O_((aq))^++ClO_(4(aq))^-`

B) To determine the concentration from pH we use the following formula:

`\begin{gathered} pH=-log[H_3O^+] \\ 1.28=-log[H_3O^+] \\ [H_3O^+]=10^(-pH) \\ [H_3O^+]=10^(-1.28) \\ [H_3O^+]=0.052\text{ }molL^(-1) \end{gathered}`

C) Determining the mass of perchloric acid used to prepare the solution, we must first determine the number of moles in the solution.

`\begin{gathered} _nHClO_4=\frac{0.052\text{ }mol*250\text{ }mL}{1000\text{ }mL} \\ _nHClO_4=0.013\text{ }mol \end{gathered}`

Mass is therefore:

`\begin{gathered} mass=\frac{moles}{molar\text{ }mass} \\ \\ mass=(0.013mol)/(100.46gmol^(-1)) \\ mass=0.000129g \end{gathered}`

Mass prepared is 1.29e-3 g.

`mass=1.29*10^(-3)g`