A polymer contains 50 molecules with molecular mass 5000, 100 molecules with molecular mass 10,000 and 50 molecules with molecular mass 15,000.Calculate number average molecular mass ?

Options

A. 5000
B. 75000
C. 10000
D. 20000

Answer

C

Explanation

Given,
For a polymer,
No. of molecules , `N_1` = 50 with molecular mass , `M_1`=5000
No. of molecules `N_2`=100 with molecular mass `M_2`=10000
`N_3=50` with `M_3=15000`
The number average molecular mass
`=(M_1N_1 + M_2N_2 + M_3N_3)/ (N_1 + N_2+N_3)`
`=((5000xx50)+(10000xx100)+(15000xx50))/(50+100+50)`
`=(250000+1000000+750000)/200=2000000/200`
=10000