Theory:

1. Calculate the mass of \(1.51\times10^{23}\) molecules of water.
 
Data:

Given molecules of \(H_2O=1.51\times10^{23}\)
 
Molecular mass of \(H_2O=18\)
 
Avogadro's number \(=6.023\times10^{23}\)
 
Solution:
 
Numberofmoles=NumberofmoleculesofwaterAvogadronumber=1.51×10236.023×1023=14=0.25mole
 
Numberofmoles=MassMolecularmass0.25=Mass18Mass=0.25×18Mass=4.5g
 
Hence, the mass of \(1.51\times10^{23}\) molecules of water \(=4.5\) \(g\)
 
 
2. Calculate the mass of \(5\times10^{23}\) molecules of glucose.
 
Data:
 
Given molecules of glucose \(=1.51\times10^{23}\)
 
Molecular mass of glucose \(=180\)
 
Avogadro's number \(=6.023\times10^{23}\)
  
Formula:
 
Massofglucose=Molecularmass×NumberofparticlesAvogadronumber=180×5×10236.023×1023=149.43g
 
Hence, the mass of \(5\times10^{23}\) molecules of glucose \(=149.43\) \(g\)