ICSE Class 10 Chemistry 2019 Solved Paper

Question : 81 of 86

Marks: +1, -0

Find the empirical formula and the molecular formula of an organic compound from the data given below :

{\C}=75.92 \%, {\H}=6.32 \% \;\text " and "\; {\N}=17.76 \%

The vapour density of the compound is 39.5 .

[ {\C}=12, {\H}=1, {\N}=14]

Solution:

\table \C,, \H,, \N ; 75.92,,6. 32,,17.76; 75. 92 \/ 12,,6 . 32 \/ 1,,17.76 \/ 14; 6.32,,6. 32,,1.26; 6.32 \/ 1 .26,,6.32 \/ 1.26,,1 .26 \/ 1.26; 5 .01,,5 . 01,,1; 5 ,:, 5 ,:, 1

Empirical formula :

{\C}_5 {\H}_5 {\N}

Empirical formula Mass

\;= {\C}_5 {\H}_5 {\N}

\;=12 × 5+1 × 5+14

\;=60+5+14=79

\;\text " V.D. "\;=39 ⋅ 5 \;\;

\;\text " Mol. Mass "\;\;=2 × \;\text " V.D. "\;

\;=2 × 39.5=79

n\;=\;{\;\text " Mol. Mass "\;}/{\;\text " Emp. formula Mass "\;}

\;=\;{79}/{79}=1

Molecular formula

\;=(\;\text " Empirical formula "\;)_n

\;= {\C}_5 {\H}_5 {\N} × 1

\;= {\C}_5 {\H}_5 {\N}

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