carbon 85.6% and H 14.4 % is their composition of mass.

what is their molecular formula

examples below
C2H6
C3H4
CH4
C2H4
C3H8

With this information one cannot determine the molecular formula. The empirical formula can be determined.

Take 100 g sample which will give you
85.6g C and 14.4g H.
Convert to moles. moles = grams/molar mass
85.6/12 = ??
14.4/1 = ??

Now find the ratio of the two elements to each other with the lowest number being 1.00. The easy way to do that is to divide the smaller number by itself. If you know the molecular formula is one of those listed, you can pick one of them. Post your work if you get stuck.

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To determine the molecular formula of a compound based on its composition of mass, you need to convert the given mass percentages into molar ratios and then simplify the ratios to obtain the simplest whole-number ratio of atoms in the compound.

Let's start with the given composition of mass:
Carbon (C): 85.6%
Hydrogen (H): 14.4%

Step 1: Convert mass percentages to molar ratios
To convert mass percentages to molar ratios, you assume you have a 100g sample of the compound. This means that in a 100g sample, you will have 85.6g of carbon and 14.4g of hydrogen.

Step 2: Convert to moles
To convert grams to moles, divide the mass of each element by its molar mass (atomic weight). The molar mass of carbon is approximately 12 g/mol, and the molar mass of hydrogen is approximately 1 g/mol.

Number of moles of carbon (n(C)) = mass of carbon / molar mass of carbon = 85.6g / 12g/mol = 7.133 moles of carbon
Number of moles of hydrogen (n(H)) = mass of hydrogen / molar mass of hydrogen = 14.4g / 1g/mol = 14.4 moles of hydrogen

Step 3: Find the simplest whole-number ratio
Divide both the number of moles of carbon and hydrogen by the smaller value to get the simplest whole-number ratio.
Dividing both values by 7.133 gives:
n(C): 1
n(H): 2

Therefore, the simplest whole-number ratio of carbon to hydrogen in the compound is 1:2.

Step 4: Write the molecular formula
Now we use the elements' symbols to represent the compound's molecular formula.
The molecular formula with a 1:2 ratio of carbon to hydrogen is CH2.

Therefore, based on the given composition of mass (85.6% carbon and 14.4% hydrogen), the molecular formula is CH2.