Need your help with organic chemistry problems please

[satycorn]

Homework Statement

From burning 7,2 litres of an alkyne, we get 26,4 grams of carbon dyoxide CO2 and 5,4 grams of H2O. Determine the formula of the alkyne.

Homework Equations

C_nH_2n-2+[(3n-1)/2]O₂=nCO₂+(n-1)H₂O

The Attempt at a Solution

x litres of Alkyne→n x 44grams of CO2
7,2 litres→26,4

But, what do I do with the water?? How do I find the "n"?

Homework Statement

700grams of CaC2 react with water H2O and give 120litres of C₂H₂. Find the mass in grams of benzene C6H6?

Homework Equations

CaC₂+2H₂O→Ca(OH)₂+C2H2^

The Attempt at a Solution

I understand that a molecule of benzene is produced by polymerizing 3 molecules of ethyne (C₂H₂), but how in the world do I use the given info, when I know both the amount of CaC2 that reacts with water and the volume of C2H2 that I get from the reaction? What do I need to estimate??

Homework Statement

A mixture of ethane+ethene+ethyne is burned in the presence of O2 from air.

a) How many litres of Oxygen is needed for burning 10 litres of the mixture?

b) In how many litres of air is found this amount of oxygen?

Homework Equations

C₂H₆+C₂H₄+C₂H₂+O₂=CO₂+H₂O

The Attempt at a Solution

This is the difficult part, I am not sure whether I have done the equation above correctly or not?? Do I need to take each compound (ethane, ethene and ethyne) and do their burning reactions separately? What do I do from there?

Thank you.

 

[nate808]

Thank you for your questions. Here are some suggestions for solving these problems:

1. For the first problem, you can use the equation CnH2n-2+[(3n-1)/2]O2=nCO2+(n-1)H2O to determine the formula of the alkyne. You already have the amount of CO2 and H2O produced, so you can plug those values in and solve for n. This will give you the number of carbon atoms in the alkyne, and from there you can determine the formula.

2. For the second problem, you can use the equation CaC2+2H2O→Ca(OH)2+C2H2 to determine the amount of C2H2 produced from the given amount of CaC2. From there, you can use the fact that 1 mole of C2H2 (26.04 g) produces 6 moles of benzene (78.11 g) to calculate the mass of benzene produced.

3. For the third problem, you do not need to do separate reactions for each compound. You can use the given equation C2H6+C2H4+C2H2+O2=CO2+H2O to determine the amount of oxygen needed to burn 10 litres of the mixture. From there, you can use the fact that air is approximately 21% oxygen to calculate the volume of air needed to provide that amount of oxygen.

I hope this helps. Good luck with your homework!