Theory:

1.  Calculate the number of molecules in \(11.2\) \(L\) of \(CO_2\) at STP.
 
Data:
 
Given volume of \(CO_2=11.2\) \(L\)
 
Molar volume of \(CO_2=22.4\) \(L\)
 
Avogadro's number \(=6.023\times10^{23}\)
 
Solution:
 
NumberofmolesofCO2=VolumeatSTPMolarvolume=11.222.4=0.5mole
 
NumberofmoleculesofCO2=NumberofmolesofCO2×Avogadronumber=0.5×6.023×1023=3.011×1023molecules
 
Therefore, the number of molecules in \(11.2\) \(L\) of \(CO_2\) at STP \(=3.011\times10^{23}\)
 
2.  Calculate the number of molecules in \(54\) \(g\) of \(H_2O\).
 
Data:
 
Given mass of \(H_2O=54\) \(g\)
 
Gram molecular mass of \(H_2O=18\) \(g\)
 
Avogadro's number \(=6.023\times10^{23}\)
 
Solution:
 
Numberofmolecules=Avogadronumber×GivenmassGrammolecularmassNumberofmoleculesofwater=6.023×1023×5418=18.069×1023
 
Therefore, the number of molecules in \(54\) \(g\) of \(H_2O=18.069\times10^{23}\) \(molecules\)