(ii) 10 g of
ammonia 
?
(b)
Calculate the total number of moles in0.585 g of sodium chloride.
(Atomic mass of N =
14 u, H = 1 u, Cl = 35.5
Answer:
(a) (i)
Molecular mass of nitrogen =2x14= 28 u Mass of 1 mole of nitrogen = 28 g
Number of
atoms in 28 g of nitrogen
= 6.022x1023
Number of
atoms in 1 g of nitrogen 
Number
of atoms in 10 g of nitrogen 
ions
Molecular
mass of ammonia = 14 + 3 x 1 =17 u
Mass of 1
mole of ammonia = 17 g
Number of
atoms in 17 g of ammonia
= 6.022x1023
Number of
atoms in 1 g of ammonia
6.022 x 1023
Number of
atoms in 10 g of ammonia
ions
10 g of 
contains more number of
atoms.
(b)
Molecular mass of sodium chloride (NaCI)
= 23+35.5=
58.5 u
58.5 g of
sodium chloride (NaCI) =1 mol
1 g of
sodium chloride (NaCl) 
mol
0.585of sodium
chloride (NaCI)
mol = 0.01 mol
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