Given information:
- An organic compound containing C, H, and O.
- Requires 2.5 L of oxygen to burn completely at STP.
- Gives two litres each of CO2 and H2O vapor.
- Empirical formula of the compound is to be determined.

Solution:
1. Determine the number of moles of CO2 produced:
- Volume of CO2 produced = 2 L
- At STP, 1 mole of any gas occupies 22.4 L.
- Therefore, number of moles of CO2 produced = 2/22.4 = 0.089 moles.

2. Determine the number of moles of H2O produced:
- Volume of H2O vapor produced = 2 L
- At STP, 1 mole of any gas occupies 22.4 L.
- Therefore, number of moles of H2O vapor produced = 2/22.4 = 0.089 moles.

3. Determine the number of moles of O2 consumed:
- Volume of O2 consumed = 2.5 L
- At STP, 1 mole of any gas occupies 22.4 L.
- Therefore, number of moles of O2 consumed = 2.5/22.4 = 0.112 moles.

4. Determine the number of moles of C, H, and O in the compound:
- Assuming the empirical formula to be CxHyOz.
- Number of moles of C = x.
- Number of moles of H = y.
- Number of moles of O = z.
- From the balanced chemical equation, the number of moles of CO2 produced is equal to the number of moles of C in the compound. Therefore, x = 0.089.
- From the balanced chemical equation, the number of moles of H2O vapor produced is equal to the number of moles of H in the compound. Therefore, y = 0.089.
- From the given information, the number of moles of O in the compound can be calculated as follows:
- Number of moles of O consumed in the reaction = 0.112.
- Number of moles of O in CO2 produced = 2x0.089 = 0.178.
- Number of moles of O in H2O produced = 2x0.089 = 0.178.
- Therefore, number of moles of O in the compound = 0.112 + 0.178 + 0.178 = 0.468.
- Simplifying the ratios of C, H, and O gives the empirical formula C2H4O.

Answer: The empirical formula of the organic compound is C2H4O.