# Question #e7817

##### 1 Answer

#### Explanation:

Your unknown compound has **molecular formula**, so you know for a fact that **mole** of this compound contains

#7# molesof carbon,#7 xx "C"# #8# molesof hydrogen,#8 xx "H"# #x# molesof oxygen,#x xx "O"#

This means that the **molar mass** of the compound can be calculated like this

#M_"M" = overbrace(7 xx "12.011 g mol"^(-1))^(color(blue)("7 moles C")) + overbrace(8 xx "1.00794 g mol"^(-1))^(color(blue)("8 moles H")) + overbrace(x xx "15.9994 g mol"^(-1))^(color(blue)(x quad "moles O"))#

#M_"M" = (94.14052 + 15.9994 * x)quad "g mol"^(-1)#

Now, you know that this compound contains **by mass**. This means that if you take the mass of **mole** of this compound, you can say that you have

#( 15.9994 * x color(red)(cancel(color(black)("g mol"^(-1)))))/((94.14052 + 15.9994 * x)color(red)(cancel(color(black)("g mol"^(-1))))) xx 100% = 26.2%# This basically means that if you take the mass of oxygen present in

#1# moleof this compound, divide it by thetotal massof#1# moleof the compound, and multiply the result by#100%# , you will end up with#26.2%# , thepercent concentration by massof oxygen.

You will thus have

# (15.9994 * x)/((94.14052 + 15.9994 * x)) xx 100 color(red)(cancel(color(black)(%))) = 26.2color(red)(cancel(color(black)(%)))#

Rearrange to solve for

#15.9994 * 100 * x = 26.2 * 94.14052 + 26.2 * 15.9994 * x#

#x * 15.9994 * (100 - 26.2) = 26.2 * 94.14052#

You will end up with

#x = (26.2 * 94.14052)/(15.9994 * (100 - 26.2)) = 2.089 ~~ 2#

You can thus say that you have