Question

Question (a)Calculate the empirical formula of a compound that has the following composition by mass. 29.0% Na, 40.5% S, O=30.4%

Answer 1

The first step to answer this question is to assume that the given percents are masses.

Then, convert these masses to moles using the corresponding molar mass:

`\begin{gathered} 29.0gNa\cdot(1molNa)/(22.98gNa)=1.26molNa \\ 40.5gS\cdot(1molS)/(32.065gS)=1.26molS \\ 30.4gO\cdot(1molO)/(15.999gO)=1.9molO \end{gathered}`

Divide each result by the least result (1.26mol):

`\begin{gathered} (1.26mol)/(1.26mol)=1 \\ (1.26mol)/(1.26mol)=1 \\ (1.9mol)/(1.26mol)=1.5 \end{gathered}`

Since not all of these are whole numbers, we have to multiply them times 2:

`\begin{gathered} 1\cdot2=2 \\ 1\cdot2=2 \\ 1.5\cdot2=3 \end{gathered}`

These numbers are the subscripts of each element in the empirical formula.

It means that the empirical formula of this compound is:

`Na_2S_2O_3`