Some Basic Concepts Of Chemistry Question 284
Question: Complete combustion of $ 0.858\ g $ of compound X gives $ 2.63\ g $ of $ CO _2 $ and $ 1.28\ g $ of $ H _2O $ . The lowest molecular mass X can have [Kerala MEE 2000]
Options:
A) $ 43\ g $
B) $ 86\ g $
C) $ 129\ g $
D) $ 172\ g $
Show Answer
Answer:
Correct Answer: A
Solution:
$ %C=\frac{12}{44}\times \frac{{W _{CO _2}}}{W}\times 100 $ $ =\frac{12}{44}\times \frac{2.63}{0.858}\times 100=83.6% $
$ %H=\frac{2}{18}\times \frac{{W _{H _2O}}}{W}\times 100 $ $ =\frac{2}{18}\times \frac{1.28}{.858}\times 100=16.4% $ $ . \begin{matrix} Element & %( a ) & At.wt.( b ) & a/b & Ratio \\ C & 83.6 & 12 & 6.96 & 1 \\ H & 16.4 & 1 & 16.4 & 2.3 \\ \end{bmatrix} \times {3 _{ _{ _{ _{ _{ _{ _{ _{ _{ _{ _{ _{ _{ _{ _{_7}}}}}}}}}}}}}}}} $
$ C _3H _7=12\times 3+7=43gm $ .
