Question

eredA compound that contains only carbon, hydrogen,and selenium is 84.9 % Se and 12.9 % C by mass.Mass spectrometry data indicate the molar mass ofthis compound is 372 g/mol. What is the molecularformula of this substance?How to enter your answer: Suppose you deduce aformula of C6H7Se5. Enter it as C6H7Se5

Answer 1

`C_4H_8Se_4`

Step-by-step explanation:

Here, we want to get the molecular formula of the substance

We start by dividing the percentages by the atomic masses of the individual elements

The atomic mass of Selenium is 79 amu

The atomic mass of Carbon is 12 amu

The atomic mass of hydrogen is 1 amu

From the given percentages, to get the percentage for hydrogen, we subtract the percentages of carbon and selenium

We have that as 100- (12.9 + 84.9) = 2.2%

We have the calculation as follows:

`\begin{gathered} Selenium \\ (84.9)/(79)\text{ = 1.075} \\ \\ Carbon \\ (12.9)/(12)=\text{ 1.075} \\ \\ Hydrogen \\ (2.2)/(1)\text{ = 2.2} \end{gathered}`

From the above, we can see that the minimum value is 1.075

Now, we divide the values by the smallest

We have that as:

`\begin{gathered} Selenium \\ (1.075)/(1.075)\text{ = 1} \\ Carbon \\ (1.075)/(1.075)\text{ = 1} \\ Hydrogen \\ (2.2)/(1.075)\text{ = 2} \end{gathered}`

We can see that the empirical formula is thus:

`CH_2Se`

Now, let us get the molecular formula

We have to find the mass of the empirical formula, then divide the molar mass by it

This will give us the required multiple needed to get the molecular formula from the empirical formula

Mathematically, we have that as:

`\begin{gathered} (79\text{ + 2\lparen1\rparen + 12\rparen n = 372} \\ 93\text{ = 372} \\ n\text{ = }(372)/(93)\text{ = 4 } \end{gathered}`

This means that the molecular formula is:

`C_4H_8Se_4`