A compound is made up of 80.0 % C and 20.0 % H. Its molar mass is 30.0 g. What is its molecular formula? a. C2H6

b. CH

c. C4H12

d. CH3

Molecular formula = C₂H₆

Explanation:

Given data:

Percentage of hydrogen = 20.0 %

Percentage of carbon = 80.0 %

Molar mass = 30.0 g  

Empirical formula = ?

Solution:

Number of gram atoms of H = 20 / 1.01 = 19.8  

Number of gram atoms of C = 80 /12 = 6.7

Atomic ratio:

            C              :           H            

         6.7/6.7        :        19.8/6.7  

            1               :           3        

C : H = 1 : 3

Empirical formula is CH₃.

Molecular formula:

Molecular formula = n (empirical formula)

n = molar mass of compound / empirical formula mass

Empirical formula = CH₃ = 12×1 +3×1.01 = 15.03 g/mol

n = 30 g/mol / 15.03 g/mol

n = 2

Molecular formula = n (empirical formula)

Molecular formula = 2 (CH₃)

Molecular formula = C₂H₆

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"among the transition metal elements, manganese and zinc have a slight lowering of electronegativities. the reason behind this is that the nuclear charges of these elements are slightly weaker than the other transition metal elements due to the way their valence electrons are filled up. both manganese and zinc have their valence electrons filled up to the 4th shell with 1 pair of electrons (4s2) completely occupying it. although the electrons in the 3rd shell (3d) are yet to be paired since the outer most shell is filled up, the ability of the nucleus to attract electrons is lessened. hence,   the electronegativity (or the ability to attract electrons) is lessened."