Question

can anyone help me out with this question pls:)

An unknown organic compound only contains carbon, hydrogen and oxygen. A 0.275g sample of the compound was combusted n excess oxygen to yeild 0.403g of CO2 and 0.165g of H2O. Determine empirica formula of the compound. Given that a 1.5g sample when vapourised occupied 0.560L at 273k and 101.3kPa, determine the molecular formula of the compound. thnks

Answer 1

Sukeena:
Step 1: How many g of C in 0.403 g CO2 and How many g of H in 0.165g water that is formed.
2. Concept: All the C and H in the CO2 and H2O came from the organic compound (CxHyOz)
3. Calculate the % of C and H and O by mass. For example %C = gC /0.275 x 100. If %C +%H does not add up to 100, you have O in it. Find that % by 100-(%C+%H)
5. Divide %C/molar mass of C to get molar ratio of . Same for H.
6. This is the molar ratio.Simplufy to whole numbers. So if it is 1.02:2.99 That is 1:3
7.This ratio is the Empirircal ratio. Gives you the value of x,y and z.
8. From the next data, use PV=nRT and calculate n = number of moles of the compound in 1.5 g.
9. Calculate the molar mass
10. Calculate the Empiritcal formula mass from step 7.
11. The molar mass should be a multiple of the Empirical formula mass.
12. Multiply x,y,z with the multiplier to get molecular formula