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Determination of the Value of the Gas Constant and the Molar Volume of Oxygen at STP

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Introduction

IB Chemistry - Practical Report Name: Chris Bolton Partner: Jamie Gearing Date(s) Conducted: 18/07/04 Topic: Application of Gas Laws Experiment: Determination of the Value of the Gas Constant and the Molar Volume of Oxygen at STP Aim: To experimentally determine the value of (I) the gas constant and (II) the molar volume of oxygen at ?SLC, and therefore to determine the molar volume of an ideal gas at STP. Hypothesis: The empirically determined values for the gas constant and the molar volume of oxygen at SLC (extrapolated to STP) should roughly approximate literature values for the gas constant (8.31 J.K-1.mol-1) and molar volume of an ideal gas (22.4 dm3.mol-1) at STP respectively, to the degrees of accuracy permitted by experimental procedure. Apparatus: MATERIALS: ? 2 grams potassium permanganate (KMnO4(s)) GENERAL: Test tube with a one-holed bung in it, retort stand, boss and clamp, rubber tubing, glass wool, 100 cm3 gas syringe, glass tubing, spatula, electronic balance SAFETY: Lab coat and safety glasses to be worn at all times. Gloves to be worn when handling potassium permanganate. Method: Refer to attached worksheet for given method AMMENDMENTS/ADDITIONS/SAFETY PRECAUTIONS: * Ensure that gas syringe plunger is not in any way impacted by wire safety cord * Ensure that plunger is entirely compressed prior to commencement * Stop heating test-tube once volume is ? 70 cm3 to avoid exceeding syringe capacity * Safety Note: Use protective gloves when handling potassium permanganate Results: Fig. ...read more.

Middle

= 0.108/32.00 n(O2) = 27/8000 ? 0.003375 mol Now divide the volume by the number of moles present; (8.25 x 10-5 m3)/(27/8000) = 0.0244 m3.mol-1 = 24.4 dm3.mol-1 The same relative/percentage errors are associated with this figure, since each value is multiplied or divided by the other in much the same fashion. Hence; Total Percentage Error (sum of all % errors): (100/27)+(50/89)+(50/589)+(2/1013) = 4.35 % ?error? = 0.0435 x 24.4 = ? 1.06 Now an absolute error has been found for the experimentally determined molar volume of oxygen at STP, so the value can be accurately expressed as: VM(STP) = 24.4 ? 1.06 dm3.mol-1 at 273 K and 101325 Pa *NOTE: This value was determined independent of the established "R" value, and is based on extrapolated ambient temperature and pressure (at STP, in fact). Comparison with Literature Values: The literature value of the Gas Constant is 8.31 J.K-1.mol-1 at 273 K and 101325 Pa. The empirically determined value found by processing the results of this experiment was 9.07 ? 0.395 J.K-1.mol-1 at 294.5 K and 101300 Pa. Clearly the conditions under which the experiment were carried out differed from STP, so results are already tainted, but the percentage difference is of some interest: ?error? = 9.07 - 8.31 = ? 0.760 relative = 0.760/8.31 = 0.0915 percentage = ? 9.15 % deviation Hence, the empirically determined "R" is approximately 9.15% off the literature value. Interestingly, 4.35% of this error has already been accounted for by systematic error calculations, leaving less than a ?5% deviation. ...read more.

Conclusion

The key improvements to this experiment would therefore include: a) Since STP would be rather difficult to simulate in a school lab, performing the experiment at SLC - with correct temperature and pressure (298 K; 101325 Pa) - is a more plausible alternative. Such a modification would allow the comparison of definite literature values with empirical results. b) Tilting the gas syringes more substantially to reduce effects of gravity on volume c) Removing safety wire holding plunger in syringe and replace with a less tense string to avoid having the syringe inhibited d) Lubricate plunger to avoid friction inhibiting plunger e) Heat the sample more gently and use less of the potassium permanganate in order that all the gaseous oxygen of the sample may be removed and the scale of the syringe is not exceeded f) Allow much more time (in the order of hours) for the apparatus to cool and for the oxygen to reach room temperature and pressure in order that calculations are valid g) Collation of multiple results, or repetition of experiment to ensure a normal distribution of results finds a reasonably accurate mean result and that random errors are gradually reduced in effect h) Use of a larger quantity of potassium permanganate and more accurate gas syringes to reduce the associated percentage errors i) Use of multiple sets of balances (ideally of greater precision) to reduce the associated systematic errors If these improvements were implemented, the accuracy of the results (and the precision with which the empirical values and the literature values matched) would certainly increase. Chris Bolton ...read more.

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