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標題:

the molecular formula

發問:

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.

最佳解答:

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

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