AP Chemistry Help

[soccer4kk]

What are the steps to solving this problem?

 

"You have just purified a natural molecular compound from the bark of a tree and analyzed some with a mass spectrometer. The compound is 51.4% Carbon, 5.75% Hdrogen, 22.8% Oxygen, and 20.00% Nitrogen. When you dissolve 5.00g of the compound in 20.0g water, the resulting solution freezes at -1.1 deggree celcius.

 

What is the molecular forumla of the compound?

 

 

[Horza2002]

First of, I would determine the empircal forumal from the elemental analysis you have been given.

 

O, and I think your missing something important about regarding the melting point bit

Edited March 6, 2011 by Horza2002

[Pwyll Pendefig Dyfed]

Calculate the number of moles of each element.

[ewmon]

This is a bit cryptic, but it works because I used it.

 

You seek the molecular formula (~number of atoms for each element) in a compound/molecule.

 

Think of — what the percent means ... and what atomic weight means ... and how they are related ... and how you can simplify the problem (in terms of what you seek). Once you obtain a representative idea of its chemical structure (ie, the relative number of atoms), simplify it to the least (whole) number of atoms for each element. Then you know it's some multiple of those numbers, and the freezing point should guide you to determine the molecule's size/overall composition.

[mississippichem]

When you dissolve 5.00g of the compound in 20.0g water, the resulting solution freezes at -1.1 deggree celcius.

 

Once you have dealt with the percent composition, it appears you have a freezing point depression problem on your hands:

 

[math] \Delta T_{f}=k_{f}mi [/math]

 

Remember that [math] k_{f} [/math] for water is [math] 1.853 K \cdot kg \cdot mol^{-1} [/math]