Post-Laboratory Questions (use the spaces provided for the answers and additiona
ID: 509513 • Letter: P
Question
Post-Laboratory Questions (use the spaces provided for the answers and additional paper ifnecessary) 1. Suppose that a student doing this experiment ran into some procedural and calculation difficulties. State the effect each of the following would have on the molar volume of O2 determined from this experiment. Briefly explain. (1) The student neglected to take into account the pressure of water vapor in the system when doing the calculations. (2) The H202 solution had decomposed slightly after standing a while, so its concentration was somewhat lower than the laboratory instructor had reported. (3) The student failed to read the barometric pressure at the time of the experiment. When she read the pressure the next day for use in her calculations, it was 0.50 in. Hg lower than it had been during the experiment.Explanation / Answer
1.
This would result in an excessively large molar volume than the actual volume.
2.
Oxygen actually produced would be less than the one reported theoritically.
3.
No effect,since we are only concerned with the change in pressure ,and not the actual values.
2(i).
Typically we may use a titrant such as KMnO4,since there will be a redox reaction
3H2O2 + 2KMnO4 gives to 3O2 + 2MnO2 + 2KOH + 2H2O
then,we will be able to relate volume and concentration of KMnO4 vs H2O2
freom total volume simply,
M H2O2=mol of H2O2 from calculation / volume used in sample.
2(ii).
When we measure molar volume of O2.
We assume that only O2 is present in gas phase.
We also assume that we can relate the volume of O2 and moles if we obtain this in water.So,
Ptotal = P - O2 + Pvapour (of water)
Also,we assume this is mainly O2 produced from the reaction and that we can relate O2 to H2O2 moles.