# Q1. Calculate the number of atoms ina) 0.5 mole atoms of nitrogenb) 0.2 mole moleules of nitrogenc) 3.2g of sulphurd)3.4 g of H2SQ2. how many molecules of water of hydration are present in 252 mg of oxalic acid?

1) (a) 1 mole of nitrogen atoms = 6.022 $×$1023 atoms
0.5 moles of Nitrogen atoms = 6.022 $×$1023 $×$ 0.5  = 3.011$×$1023 atoms

(b) 1 mole of nitrogen molecules  = ​ 6.022 $×$1023  molecules
0.2 moles of nitrogen molecules = 6.022 $×$1023 $×$ 0.2  = 1.2044$×$1023 molecules
As 1 molecule of nitrogen contains 2 atoms of nitrogen.
So, ​1.2044$×$1023 molecules of nitrogen will contain 1.2044$×$1023$×$ 2 atoms
= 2.4088 $×$1023 atoms

(c) 32 g of sulphur (Molar mass of Sulphur ) = 6.022 $×$1023 atoms
3.2 g of sulphur  =
= 0.6022 $×$1023 atoms

(d) 3.4 g of H2S
Molar mass of H2S = 34 g mol-1
34 g of H2S contains 6.022$×$1023 molecules
1 molecule of H2S contain 2 atom of hydrogen and 1 atom of sulphur.
34 g of H2S contain 2$×$6.022$×$1023 atoms of hydrogen and 6.022$×$1023 atoms of Sulphur.
3.4 g of H2S contain 12.044$×$1022 atoms of hydrogen and 6.022$×$1023 atoms of sulphur.
2) Molecular formula of oxalic acid is H2C2O4.2H2O
and molar mass of oxalic acid  =  gmol-1
water molecule in 1 mole oxalic acid  = 2 molecules
So, 126 g of oxalic acid contains 2 $×$ 6.022 $×$1023 molecules of water.
thus, 0.252 g of oxalic acid will contain =
=  2.409  $×$1021 molecules of water

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