Chemistry:

30cm^3 of a mixture of methane and ethyne require 70cm^3 of oxygen for complete combustion. Calculate the composition of the mixture

You'd get help if you put your school SUBJECT in the right place.

Eh. It could possibly be on a chemistry test. I don't see why, but it could be.

Could be because it IS chemistry. See the post above.

To calculate the composition of the mixture, we need to find the moles of methane and ethyne present in the mixture.

Step 1: Determine the moles of oxygen used for complete combustion:
Since 70 cm^3 of oxygen is required for complete combustion, we can assume that the oxygen is in excess. The balanced equation for the complete combustion of methane is:

CH4 + 2O2 -> CO2 + 2H2O

Using the stoichiometry of the balanced equation, we find that for every mole of CH4, we need 2 moles of O2. Therefore, the moles of O2 used can be calculated as:

70 cm^3 O2 x (1 mole O2/22.4 L O2) = moles of O2

Step 2: Calculate the moles of methane (CH4):
Knowing the moles of O2 used, we can determine the moles of CH4 using the mole ratio from the balanced equation:

1 mole CH4 : 2 moles O2

So, the moles of CH4 can be calculated as:

1/2 x moles of O2 = moles of CH4

Step 3: Calculate the moles of ethyne (C2H2):
The balanced equation for the complete combustion of ethyne is:

C2H2 + 2.5O2 -> 2CO2 + H2O

Using the stoichiometry of the balanced equation, we find that for every mole of C2H2, we need 2.5 moles of O2. Therefore, the moles of C2H2 can be calculated as:

1/2.5 x moles of O2 = moles of C2H2

Step 4: Calculate the volume of methane and ethyne:
We can calculate the volume of methane and ethyne using the ideal gas equation:

PV = nRT, where P is the pressure (assume constant), V is the volume, n is the number of moles, R is the ideal gas constant (0.082 L.atm/mol.K), and T is the temperature (assume constant).

Since the pressure and temperature are constant, we can rearrange the equation:

V/n = constant

Therefore, the ratio of the volumes to the moles of each gas will be constant.

Let's assume that the volume of methane is V1 and the volume of ethyne is V2. Then, we have the following ratio:

V1/V2 = moles of CH4 / moles of C2H2

Using the values calculated in steps 2 and 3, you can determine the ratio of the volumes.

Finally, determine the composition of the mixture: The composition of the mixture is given by the ratio of the volumes of methane to the volume of the mixture, which can be calculated as:

Volume of methane / (Volume of methane + Volume of ethyne) x 100%

This will give you the composition of the mixture in terms of the percentage of methane present. To obtain the composition of ethyne, subtract this percentage from 100%.