Finding molecular formula from volume of products

[Ose90]

Hello sir and madam, I would be grateful if you can help me solve this question.

6.0 cm^3 of a gaseous hydrocarbon was sparked with 34.5 cm^3 of oxygen. The volume of the gaseous products after cooling to room temperature was 22.5 cm^3. The volume was reduced to 4.5 cm^3 on passing the gases through aqueous potassium hydroxide. What is the molecular formula of hydrocarbon?

my doubts : First, I try calculating the volume of CO2 produced and It is 18cm^3 and the volume of H2O is apparently 4.5 cm^3. What should I do next? How to find the volume of oxygen gas that has reacted? Should I convert them into moles by dividing the volume of room temperature? I'm confused :(

Thanks in advance.

 

[Ose90]

Sry I have posted this thread in the wrong section.

Thread should be closed, sorry moderator.

 

[quicknote]

Dear scientist,

Thank you for reaching out for assistance with your question. To determine the molecular formula of the hydrocarbon, we can use the information provided to calculate the moles of each gas involved in the reaction.

First, we need to determine the moles of CO2 produced. From the ideal gas law, we know that the number of moles of a gas is equal to its volume divided by its molar volume at STP (standard temperature and pressure). At STP, the molar volume of a gas is 22.4 L/mol. Therefore, the moles of CO2 produced can be calculated as follows:

moles CO2 = 18 cm^3 / (22.4 L/mol * 1000 cm^3/L) = 0.0008 moles

Similarly, we can calculate the moles of H2O produced:

moles H2O = 4.5 cm^3 / (22.4 L/mol * 1000 cm^3/L) = 0.0002 moles

Next, we need to determine the moles of oxygen that reacted. We know that the initial volume of oxygen was 34.5 cm^3 and the final volume after the reaction was 22.5 cm^3. Therefore, the volume of oxygen that reacted is 34.5 cm^3 - 22.5 cm^3 = 12 cm^3. Using the same calculation as above, we can determine the moles of oxygen that reacted:

moles O2 = 12 cm^3 / (22.4 L/mol * 1000 cm^3/L) = 0.0005 moles

Now, to find the molecular formula of the hydrocarbon, we need to use the ratio of moles between the hydrocarbon and oxygen. From the balanced chemical equation, we know that for every 1 mole of hydrocarbon, 3 moles of oxygen are required for complete combustion. Therefore, the ratio of moles between the hydrocarbon and oxygen is 1:3.

Since we have calculated the moles of CO2 and H2O, we can use the ratio of moles to determine the moles of the hydrocarbon. From the ratio, we know that for every 1 mole of CO2 produced, 1 mole of hydrocarbon was consumed. Therefore, the moles of the hydrocarbon can be calculated as:

moles hydrocarbon