Oxalic acid is an organic substance. Its composition is 26.7% , 2.2% , and 71.1% (by mass), and its molecular weight is 90 amu. What is its molecular formula?

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Oxalic acid is an organic substance. Its composition is 26.7% C, 2.2% H, and 71.1% O (by mass), and its molecular weight is 90 amu. What is its molecular formula?

Answer : The molecular formula of a compound is,

Solution : Given,

If percentage are given then we are taking total mass is 100 grams.

So, the mass of each element is equal to the percentage given.

Mass of C = 26.7 g

Mass of H = 2.2 g

Mass of O = 71.1 g

Molar mass of C = 12 g/mole

Molar mass of H = 1 g/mole

Molar mass of O = 16 g/mole

Step 1 : convert given masses into moles.

Moles of C =

Moles of H =

Moles of O =

Step 2 : For the mole ratio, divide each value of moles by the smallest number of moles calculated.

For C =

For H =

For O =

The ratio of C : H : O = 1 : 1 : 2

The mole ratio of the element is represented by subscripts in empirical formula.

The Empirical formula =

The empirical formula weight = 1(12) + 1(1) + 2(16) = 45 gram/eq

Now we have to calculate the molecular formula of the compound.

Formula used :

Molecular formula =

Therefore, the molecular of the compound is,