Finding Molecular formula from a given molecular mass and equation.

In summary, using the given information, 1g of a compound reacted completely with oxygen to produce 2.2 g CO2 and 1.2 g H2O. The molar mass is approximately 60. Various calculations were made to determine the number of moles of each compound and the molar ratio of carbon and hydrogen. However, the molecular formula of the compound remains unknown and further calculations using empirical formula methods may be necessary.
  • #1
SaRaH...
7
0
The question is as follows:
A compound contains only carbon, hydrogen and oxygen. When 1g of the compound is reacted completely with oxygen, 2.2 g CO2 and 1.2 g H2O are obtained. The molar mass is close to 60. What is the molecular formula?

I first wrote the equation: compound + O2 = CO2 +H20 (is this right?)

Using the equation no.moles = no. grams/molar mass I found the number of moles of each to be:
compound: ~0.0167mol
O2: no. grams/32
CO2: 0.05mol
H2O: 0.067mol

Using these I found that (if the above equation is right) that the amount of the compound used is ~ 4.012*amount of H2O produced.

I also found the molucular mass of the compound CxHyOz to be: 12x+y+16z = 60

I'm not sure if everything I tried was necessary or correct however now I seem to be going around in circles with everything I do and can't seem to be able to reach an answer.

Any help in solving this would be very much appreciated.
Thanks,
Sarah.
 
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  • #2
SaRaH... said:
I first wrote the equation: compound + O2 = CO2 +H20 (is this right?)

Yes and no. Yes - that's a correct skeletal equation describing what is going on. No - it is not balanced (it can't be as long as you don't have your compound formula) and it doesn't help much.

compound: ~0.0167mol

That's not incorrect, but at this moment it is irrelevant.

O2: no. grams/32

You don't know number of grams of oxygen (yet) so while it is correct, it is not yet useful. Can you calculate how much oxygen was in the 1g of the compound?

CO2: 0.05mol
H2O: 0.067mol

That's the most important information at this stage. Molar ratio of these compound is linked to molar ratio of carbon and hydrogen in the original compound. Can you calculate how many atoms of hydrogen were there for each atom of carbon? For two atoms of carbon? For three?

I also found the molucular mass of the compound CxHyOz to be: 12x+y+16z = 60

That's correct, but not necesarilly required.

Check your textbook for empirical formula calculation.

--
methods
 

1. How do you find the molecular formula from a given molecular mass and equation?

The molecular formula can be found by first calculating the molar mass of the compound using the given molecular mass. Then, divide the molar mass of the compound by the molar mass of each individual element in the compound. This will give you the ratio of each element present in the compound, which can then be used to determine the molecular formula.

2. Can the molecular formula be determined from just the molecular mass and equation?

Yes, the molecular formula can be determined from just the molecular mass and equation as long as the equation is balanced and all reactants and products are known. However, it is always helpful to have additional information such as the molar mass of the compound or the ratios of elements present in the compound.

3. What is the significance of finding the molecular formula?

The molecular formula provides important information about the composition of a compound. It tells us the types and numbers of atoms present in the compound, which can help us understand its properties and potential uses. Knowing the molecular formula is also crucial for accurately naming a compound according to the rules of nomenclature.

4. Can the molecular formula be determined for all compounds?

No, the molecular formula can only be determined for compounds that are made up of discrete molecules. Some compounds, such as ionic compounds, do not exist as discrete molecules and therefore do not have a molecular formula. These types of compounds are typically named based on their empirical formula.

5. Are there any shortcuts or tricks for finding the molecular formula from a given molecular mass and equation?

There are no shortcuts or tricks for finding the molecular formula. The process involves careful calculation and consideration of the ratios of elements in the compound. However, with practice and knowledge of basic chemistry principles, the process can become easier and more efficient.

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