Problem: A gaseous hydrogen and carbon containing compound is decomposed and found to contain 82.66% carbon and 17.34% hydrogen by mass. The mass of 158 mL of the gas, measured at 556 mmHg and 25 oC, was found to be 0.275 g.What is the molecular formula of the compound?

FREE Expert Solution

We’re being asked to determine the molecular formula of a compound composed of C and H given the mass percent of C and H. This means we need to do the following steps:


Step 1: Calculate the mass and moles of C and H in the compound.

Step 2: Determine the lowest whole number ratio of C and H to get the empirical formula.

Step 3: Get the ratio of the molar mass and empirical mass to determine the molecular formula.


Step 1: The compound is composed of C and H and we’re only given the mass percent of C (82.66% C) and H (17.34% H)


Recall that mass percent is given by:


%Mass=mass of Xtotal mass×100



Assuming we have 100 g of the compound, this means we have 82.66 g C and 17.34 g H. Now, we need to get the moles of each element in the compound. The atomic masses are 12 g/mol C and 1 g/mol H.


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Problem Details

A gaseous hydrogen and carbon containing compound is decomposed and found to contain 82.66% carbon and 17.34% hydrogen by mass. The mass of 158 mL of the gas, measured at 556 mmHg and 25 oC, was found to be 0.275 g.

What is the molecular formula of the compound?

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