# 10. Phenylmagnesium bromide is used as a Grignard reagent in organic synthesis.Deternine its empirical and rnolecular formula if its molar mass is 181.313 g/rnol anditcontains39.7458% C, 2.77956% H, 13.4050 % Mg, and 44.0697%Br. (WS 1)

Molar mass of hydrogen = 1 g
Given mass of hydrogen = 2.77956 g
Number of moles = Given mass / molar mass = 2.77956 / 1 = 2.77956 moles
Molar mass of carbon = 12 g
Given mass of carbon = 39.7458 g
Number of moles = 39.7458 / 12 = 3.312 moles
Molar mass of Magnesium = 24 g
Given mass of magnesium = 13.4050 g
Number of moles = 13.4050 / 24 = 0.558 moles
Molar mass of Bromine = 80 g
Given mass of bromine = 44.0697 g
Number of moles = 44.0697 /80 = 0.55 moles

Dividing the number of moles by the smallest number i.e. 0.55
Hydrogen  = 2.779 / 0.55 = 5
Carbon = 3.312 / 0.55 = 6
Bromine = 0.55 / 0.55 = 1
Magnesium = 0.55 / 0.55 = 1
Hence , its empirical formula is C6H5MgBr  .
Molar mass is 181. 313 g /mol
n = Molar mass / empirical molar mass
Empirical molar mass = 6$×$12 + 5$×$1 + 24 + 80 = 181 g
Hence , n = 181 /181 = 1
Hence , the molecular formula is also C6H5Br .

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