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In 100 g of naphthalene ,  2.423 g of S was dissolved . Melting point of naphthalene is 80.1 celcius .Tf is 661 celcius . Lf is 35.7 cal/g of naphthalene . Molecular formula of sulphur added is

(a)S2

(b)S4

(c)S6

(d)S8

Asked by Balbir 17th July 2019, 4:48 PM
Answered by Expert
Answer:
Given: 
Melting point of napthalene Tf = 80.1ºC = 353K
Lf = 35.7 cal/g
W= 0.661
WB = 2.423g
 
Formula used:
 
straight K subscript straight f equals fraction numerator RT subscript straight f superscript 2 over denominator 1000 cross times straight L subscript straight f end fraction
And the formula for depression in freezing point,
 
increment straight T subscript straight f equals straight K subscript straight f space space end subscript cross times fraction numerator straight W subscript straight B over denominator straight W subscript straight A cross times straight m subscript straight B end fraction space cross times 1000

increment straight T subscript straight f equals space fraction numerator RT subscript straight f superscript 2 over denominator 1000 cross times straight L subscript straight f end fraction cross times fraction numerator straight W subscript straight B over denominator straight W subscript straight A cross times straight m subscript straight B end fraction space cross times 1000

straight m subscript straight B space equals fraction numerator RT subscript straight f superscript 2 over denominator 1000 cross times straight L subscript straight f end fraction cross times fraction numerator straight W subscript straight B over denominator straight W subscript straight A cross times increment straight T subscript straight f end fraction space cross times 1000 space space


straight m subscript straight B space equals fraction numerator 2 cross times left parenthesis 353 right parenthesis squared over denominator 1000 cross times 35.7 end fraction cross times fraction numerator 2.423 over denominator 0.661 cross times 100 end fraction cross times 1000 space space space................... The space value space of space straight R space taken space as space 2 space in space calories.


straight m subscript straight B space equals 249218 over 35700 cross times fraction numerator 2423 over denominator 66.1 end fraction

straight m subscript straight B space equals 6.98 cross times 36.66

straight m subscript straight B space equals space 255.86 space almost equal to 256
 
Since, the atomic weight of sulphur is 32 and its molecular mass is 256, therefore number of sulphur atoms associated to form a single molecule is 256 over 32 space equals space 8
Hence the molecular formula of sulphur is S8
 
 
 
 
 
 
Answered by Expert 22nd July 2019, 5:27 PM
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