Finding Molecular X

[Johanna Caprietta 1E]

The past two weeks we have gone over questions about solving for both the Empirical and Molecular formula. I understand how to solve these problems when I am given the molecular compound and molar mass. How do I go about solving the problem if I am not given the molecular compound?

[tmehrazar]

What do you mean exactly, could you provide an example?

[Odalys Cuevas 1C]

Do you mean when you are just given the name? For example Nitrogen trifluoride so then you have to figure out what that compound is.

[Johanna Caprietta 1E]

Say for example problem F.13 where 4.14 g of phosphorus is combined with chlorine to produce 27.8g of a white compund. The problem then ask to find the empirical formula. What would be the steps to solve this problem?

[Betty Wolkeba section 1L]

What do you mean by molecular compound? Are you talking about when they give us the name and not the compound? Because if thats the case, we havent learned how to form molecular compounds from names yet

[chemlover]

I don't believe we have gone over that, I would ask a TA or Dr.Lavelle on Monday!

[Johanna Caprietta 1E]

Okay I found an example of what I was referring to. The questions states "A combustion analysis was conducted on an unknown molecule. After 28.4 grams of the unknown molecule was combusted, 43.82 grams of carbon dioxide and 16.44 grams of water were produced. The molecular mass of molecule is 342.3g/mol. What is the empirical formula of the unknown molecule?" I was wondering if anyone could help me with steps in order to solve this problem.

[Betty Wolkeba section 1L]

First I would solve for the number of moles produced for each product but break it down to C,H,O. Then divide each of the moles you got by the lowest number of moles produced. Then you would use those values for the empirical. To find the molecular formula, just divide the given molecular mass by the molecular mass you calculated from the empirical. Then multiply that number by the empirical to find the molecular.

[Hongtao Yao]

In the case of the example you mentioned, you need to figure out what will be produced as the result of the reaction just by the properties of the reactant you are given.

[Jaquelinne Rodriguez-Lopez 1L]

For combustions problems, you most likely need to use Avogadro's constant to find mols before proceeding to find the mass percentage. Also, if you haven't already, sign up for peer learning sessions with AAP. We went over this last week.