Homework Help: Chemistry

Posted by Louis on Sunday, September 18, 2011 at 10:19pm.

A 185.325 g sample of a compound of carbon, nitrgoen and hydrogen is burned completely. Calculate the empirical formula if 225.0 g of water and 230.0 g of NO2 is formed. In another experiment the sample was found to have a density of 10.9 g/L at 1.20 atm and 25.0 degrees Celsius. What is the molecular formula of the compound?

Chemistry - DrBob222, Monday, September 19, 2011 at 12:45am
Convert 225.0g H2O to g H. Convert 230.0g NO2 to g N.
185.325-gH-gN = gH.

Using moles = grams/atomic mass, convert g C, g H, and g N to moles.

Then find the ratio of each element to each other with the smallest number being 1.00. The easy way to do that is to divide the smallest number by itself, then divide the other numbers by the same small number. Round to whole numbers of multiply by 1, 2, 3, 4, etc to obtain values that are close enough to whole numbers to round to them. That will be the empirical formula.
The molar mass will be given by
Pressure*molar mass = density*R*T
Solve for molar mass.
Finally, the molecular formula is given by (molar mass/empirical mass)_n where n is rounded to a whole number.

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