Calculate the number of molecules present in the following substance
a) 90g water `(H_2 O)`
b) 34g Ammonia `(NH_3)`
c) 5 mole Hydrogen `(H_2)`
d) 10 mole chlorine `(Cl_2)`

Explanation

a) Number of molecules
=`(mass in gram/ gram molecular mass xx 6.022 xx 10^23)`
`(90/18) xx 6.022 xx 10^23 = 12.044 xx 10^23`
b) Mass in gram = 34g
gram molecular mass `(NH_3)` =17g
Number of molecules
= `number of moles xx 6.022 xx 10^23`
` 5 xx 6.022 xx 10^23 = 60.22 xx 10^23`
`= 10 xx 6.022 xx 10^23 = 60.22 xx 10^23`