Some Basic Concepts Of Chemistry Question 276
Question: If $ 10^{21} $ molecules are removed from 200mg of $ CO _2 $ , then the number of moles of $ CO _2 $ left are [IIT 1983]
Options:
A) $ 2.85\times {10^{-3}} $
B) $ 28.8\times {10^{-3}} $
C) $ 0.288\times {10^{-3}} $
D) $ 1.68\times {10^{-2}} $
Show Answer
Answer:
Correct Answer: A
Solution:
200mg of $ CO _2 $ = $ 200\times {10^{-3}}=0.2gm $
44gm of $ CO _2 $ = $ 6\times 10^{23} $ molecules 0.2gm of $ CO _2 $ = $ \frac{6\times 10^{23}}{44}\times 0.2=0.0272\times 10^{23} $
$ =2.72\times 10^{21} $ molecule Now $ 10^{21} $ molecule are removed. So remaining molecules $ =2.72\times 10^{21}-10^{21} $ $ =10^{21}(2.72-1) $ = $ 1.72\times 10^{21} $ molecules Now, $ 6.023\times 10^{23} $ molecules = 1mole $ 1.72\times 10^{21} $ molecules $ =\frac{1\times 1.72\times 10^{21}}{6.023\times 10^{23}}=0.285\times {10^{-2}} $
$ =2.85\times {10^{-3}} $ .
