Question

What is the molecular formula of the compound whose molar mass is 120.2 g/mol and empirical formula is SiO2?


@JoannaBlackwelder @aaronq

Answer 1

This one confuses me even more:

A compound is found to be 85.6% C and 14.4% H. Its molecular mass is 42.1 g. What is its molecular formula?
A. CH
B. CH6
C. C3H6
D. C6H12

Is it C?

Answer 2

For the first one,

Silicon atomic mass - about 28.02 g/mol
Oxygen atomic mass - about 16 g/mol

The empirical formula shows a ratio of one silicon to 2 oxygens, and has a mass of
SiO2 - 28.02 + 2(16) = 60.02 g/mol

The compound you are looking for has atomic mass 120.2 g/mol
\[\frac{ 120.2 }{ 60.02 } \approx 2\]

2x [SiO2] --->
Si2O4

Answer 3

The second one with the percents i am guessing goes something like this ...

Carbon - 85.6% of the 42.1g molecular mass

42.1*0.856 = 36.037 g of Carbon molecular mass

Molecular mass of carbon is about 12.01 grams per mol
\[\frac{ 36.037 }{ 12.01 } = 3~~carbon ~atoms\]

Hydrogen - 14.4% of the 42.1 g molecular mass
42.1*0.144 = 6.06 g of Hydrogen Molecular mass

Molecular mass of hydrogen is about 1.008 grams per mole

\[\frac{ 6.06 }{ 1.008 } \approx 6~hydrogen~atoms\]

Overall: \[\large\color{blue}{ C _{3}H _{6}}\]

Answer 4

@DanJS
Does the chemical formula MgCl2 represent a molecule or a formula unit?
A. Molecule
B. Formula unit