1. the molecular formula of sulphuric acid is H2SO4: (a) calculate the molecular mass of sulphuric acid. (b) how many moles are there in 9.8g of sulphuric acid ? (c) how many "gram-atoms" of each element are there in 9.8g of sulphuric acid ? (atomic masses: H = 1, S = 32, O = 16) 2. Find the number of molecules present in a drop of chloroform (CHCl3) weighing 0.0239g. (C = 12, Cl = 35.5, H = 1)

1) a) Molecular mass of sulphuric acid (H2SO4) = 2$×$1 + 32 + 16$×$4 = 98 u

b) Given mass of H2SO4 = 9.8 g
Number of moles (n) of H2SO4 =
n = $\frac{9.8}{98}$ = 0.1 moles

c) 98 g of H2SO4 contains = 32 g of sulphur
9.8 g of H2SO4 contains =  $\frac{32}{98}×9.8$ = 3.1 gram sulphur atoms
98 g of H2SO4 contains = 2 g of hydrogen atoms
9.8 g of H2SO4 contains = $\frac{2}{98}×9.8$ = 0.2 gram hydrogen atoms
98 g of H2SO4 contains = 64 g of oxygen atoms
9.8 g of H2SO4 contains = $\frac{64}{98}×9.8$ = 6.39 gram oxygen atoms

2)  Molar mass of chloroform (CHCl3) = 12 + 1 + 3$×$35.5 = 119.5 g mol-1
119.5 g of CHCl3 contains = 6.022$×$1023 molecules
0.0239 g of CHCl3 = $\frac{6.022×{10}^{23}}{119.5}×0.0239$ = 0.0012 molecules

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a) molecular mass=(1*2)+(32)+(16*4)=82u.

b)9.8/82=0.119

c)1mole=6.022*10^23molecules

0.119=6.022*10^23*0.119

=0.719*10^23molecules

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