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# Chemistry Question Help watch

1. Which volume of oxygen gas, at room temperature and pressure, is required for complete combustion of 1.25 × 103 mol of propan-1-ol?

A 105 cm3
B 120 cm3
C 135 cm3
D 120 cm3

Choose one
2. 1. Write out the equation for the complete combustion of propan-1-ol
2. Balance the equation
3. Determine moles of oxygen using molar ratios
4. Multiply moles of oxygen by 24000 to determine volume occupied by oxygen
3. Write out the equation for the complete combustion of propan-1-ol. Work out the number of moles of O2 in this combustion using the ratios and the moles you have. Rearrange moles = mass/mr to find mass - 1g = 1cm^3 and therefore you have your answer.
4. (Original post by ReeceM1)
1. Write out the equation for the complete combustion of propan-1-ol
2. Balance the equation
3. Determine moles of oxygen using molar ratios
4. Multiply moles of oxygen by 24000 to determine volume occupied by oxygen
Multiply by 24000? Why?
5. (Original post by Kozmo)
Multiply by 24000? Why?
1 mol of gas occupies 24 dm^3 at RTP. The answers are given in cm^3, so you multiply by 24000 as there are 1000 cm^3 in a dm^3.

(Original post by Kozmo)
Write out the equation for the complete combustion of propan-1-ol. Work out the number of moles of O2 in this combustion using the ratios and the moles you have. Rearrange moles = mass/mr to find mass - 1g = 1cm^3 and therefore you have your answer.
1g = 1cm^3 for water
6. (Original post by ReeceM1)
1 mol of gas occupies 24 dm^3 at RTP. The answers are given in cm^3, so you multiply by 24000 as there are 1000 cm^3 in a dm^3.

1g = 1cm^3 for water
Ah yes, you're right.
And in reference to the 1g = 1cm^3, I've seen a mark scheme answer just using volume (1cm^3) in place of mass in this equation. As far as I can recall, it wasn't waster and just used as volume in cm^3 as opposed to mass in grams.
7. Thanks Guys

I was really stuck on this question (i don't know why) it sounds easy now its explained. Its from the new specification for A-level so they decide to put in multiple choice and all that

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