the molecular formula

2011-09-29 11:39 pm

Please explain, THX

A compound with molecular mass of 88g is found to contain carbon, hydrogen and oxygen on combustion. 5.17mg of this compound gives 10.32mg of carbon dioxide and 4.32mg of water. Determine the molecular formula of this compound.

回答 (1)

某某

2011-09-30 3:50 am

✔ 最佳答案

let the molecular formula be CxHyOz,

CxHyOz + (x+y/4-z/2)O2 -------------------> xCO2 + (y/2)H2O

5.17mg 10.32mg 4.32mg

no. of mole of carbon dioxide
=(10.32/1000)/(12+16x2)
= 0.00023455mole
no. of mole of water
=(4.32/1000)/18
=0.00024mole

by comparing the mole ratio
we got the result x=y/2 y=2x

CxH2xOz + (3x/2-z/2)O2 -------------------> xCO2 + xH2O

5.17mg 10.32mg 4.32mg

no.of mole of CxH2xOz
= (5.17/1000)/88
=0.00005875

by comparing the mole ratio
we got the result
0.00024/0.00005875=x
x=4
y=2x=8
12x+2x+16y=88
14x+16y=88
14(4)+16y=88
y=2

so the molecular formula is C4H8O2

參考: me

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