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Business homework help. It depends on the information you have.
The empirical formula tells us the simplest whole-number ratio of the different types of atoms in a compound.
FROM THE MOLECULAR FORMULA
If you know that the molecular formula of butane is C?H??, then you divide the subscripts by their highest common factor (2).
This gives you the empirical formula C?H?.
FROM PERCENTAGE COMPOSITION
You can calculate the empirical formula from percentage composition.
Example
Butane is 82.66 % C and 17.34 % by mass. What is its empirical formula?
Solution
Assume 100 g of butane. Then you have 82.66 g of C and 17.34 g of H.
Moles of C = 82.66 g C ? ##(1″mol C”)/(12.01″g C”)## = 6.8826 mol C
Moles of H = 17.34 g H ? ##(1″mol H”)/(1.008″g H”)## = 17.202 mol H
##”Moles of C”/”Moles of H” = (6.8826″mol”)/(17.202″mol”) = 1/2.4994 =2/4.9988 ÷ 2/5##
? The empirical formula of butane is C?H?.
FROM COMBUSTION ANALYSIS
You can calculate the empirical formula by doing a combustion analysis.
You burn a sample of butane and measure the masses of CO? and H?O produced.
Example
The combustion of a sample of butane produces 1.6114 g of carbon dioxide and 0.8427 g of water. What is the empirical formula of butane?
Solution
Moles of C = 1.6114 g CO? ? ##(1″mol CO?”)/(44.01″g CO?”) ? (1″mol C”)/(1″mol CO?”)## = 0.036 614 mol C
Moles of H = 0.8247 g H?O ? ##(1″mol H?O”)/(18.02″g H?O”) ? (2″mol H”)/(1″mol H?O”)## = 0.091 532 mol H
##”Moles of C”/”Moles of H” = (0.036 614″mol”)/(0.091 532″mol”) = 1/2.5000 =2/5.0000 ÷ 2/5##
? The empirical formula of butane is C?H?.

Very good explanation, large fond, video on this page: https://www.boundless.com/chemistry/textbooks/boundless-chemistry-textbook/atoms-molecules-and-ions-2/chemical-formulas-37/empirical-formulas-210-587/

Business homework help