Qualification > Sciences

Chemistry- need help mcq questions plz!!!

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Deadly_king:

--- Quote from: $!$RatJumper$!$ on November 17, 2010, 07:08:19 am ---Many thankx :)

--- End quote ---

Mention not dude ;)

$!$RatJumper$!$:
Answer is actually C.. :/

elemis:

--- Quote from: $!$RatJumper$!$ on November 17, 2010, 09:21:23 am ---Answer is actually C.. :/

--- End quote ---

I think I remember this question. The answer is C3H8 right ?

I'll explain how.

elemis:
10 CxHy + 50 O2 ----------> 30 CO2 + 40 H2O

Since 10 cm3 of the Hydrocarbon is used along with 70 cm3 of Oxygen the hydrocarbon is the limiting agent. Hence, 10 moles of Hydrocarbon reacted.

Since 20 cm3 of Oxygen is left unreacted we insert 50 moles into our equation (above).

We are told there are 30cm3 of CO2 so we insert 30 moles into the equation.

Only H2O remains unbalanced. So we insert 40 moles of H2O to balance it.

We have a balanced equation.

We simplify the molar ratios by dividing by ten to give :

1 CxHy + 5 O2 ----------> 3 CO2 + 4 H2O

Notice there are 3 moles of C on the products side as well as 8 (4*2) moles of H ?

Therefore, the hydrocarbon must be of formula C3H8

$!$RatJumper$!$:
Thankx but why are there 40 moles of water?

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