The molecular mass of a compound is 75
(i) Calculate the mass of 100 molecules, in amu.
(ii) Calculate the mass of 5000 molecules , in gm.
(iii) What is the mass of `6.022xx10^(20)` molecules , in gm
(iv) How many molecules are in its 2.5 mg


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(i) mass of 1 molecules =75 amu
`therefore` mass of 100 molecules=7500 amu
(ii) Mass of 5000 molecules =`5000xx75` amu
`=5000xx75xx1.67xx10^(-24)=6.26 25xx10^(-19)` gm
`because 6.022xx10^(20)` molecules weights `(75)/(6.022xx10^(23))xx6.022xx10^(20)=0.075` gm
(iv) `therefore `75 gm compound contains `6.022xx10^(23)` molecules
`because 2.5xx10^(-3)` gm will contain `(6.022xx10^(23))/(75)xx2.5xx10^(-3)=2.007xx10^(19)` molecules.

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