How to Figure out the Molecular Formula from the Percentage Composition – Part 1

Molecular formula simply indicates the numbers of each type of atom in a molecule of a chemical compound.


The empirical formula of a chemical compound is the simplest whole number ratio of atoms present in a compound.

The molar mass (aka molecular weight or formula weight) of a chemical substance (element or compound) is defined as the ratio of the mass to the amount of substance measured in moles of any sample of the substance, is a bulk, not molecular, property of a substance, and is a weighted average of many instances of the element or compound, which often vary due to the difference in isotopic abundances.

The molar mass is considered to be a whole number or a number having one decimal place for the ease of calculations.

Question:

A welding fuel gas contains carbon and hydrogen only. Burning a small sample of it in oxygen gives 3.38 g Carbon dioxide, 0.690 g of water and no other products. A volume of 10.0 L (measured at STP) of this welding gas is found to weigh 11.6 g. Calculate the molecular formula of the gas.

Solution:



Click to enlarge the image

RMM = Relative molar mass

Frenzy formulae❓ Let Chemaficionado know at mychemistryhomework@gmail.com❗

References:

(1)    Wikipedia Contributors. Empirical formula. Wikipedia. https://en.wikipedia.org/wiki/Empirical_formula.

‌(2)    Wikipedia Contributors. Chemical formula. Wikipedia.

(3)    Wikipedia Contributors. Molar mass. Wikipedia. https://en.wikipedia.org/wiki/Molar_mass.

‌(4)    Brown, C.; Ford, M. Higher Level Chemistry, 2nd ed.; Pearson Education: Harlow, Essex, 2014.

(5)    Ncert. Chemistry : Textbook for Class XI - Part.I; National Council Of Educational Research And Training: New Delhi.

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