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Chemistry lab reort-molar volume of hydrogen

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Introduction

IB Chemistry DCP and CE Hao Sun Molar Volume of Hydrogen Gas Youhyun Lee 11(1) Trial 1 Raw Data Table Mass of magnesium () 0.045 Temperature of water () 25.0 Temperature of air () 20.0 Initial volume of HCl () 47.40 Final volume of HCl () 3.50 Height of HCl column () 6.5 Reference Data Table Atmospheric pressure () 102.44 Vapor pressure of water (kPa) 3.17 at 25.0 * The reference data was provided by the supervisor. Observation Tiny little bubbles were squirting up from the bottom when the magnesium ribbon was inserted into the burette. The magnesium reacted with hydrochloric acid to produce hydrogen gas. However, less bubbles of hydrogen gas were produced and the reaction was relatively slower than in other groups. As time elapsed, bubble rising velocity and the amount of bubbles were reduced. Big bubbles were intermittently produced by the magnesium and the time interval between successive bubbles became longer as the reaction went to completion. During this time, many tiny bubbles were trapped in the plastic gauze and failed to move up to the surface of the solution. At the beginning of the reaction, a continuous small stream of solution flows from the burette in the water. As time elapsed, the stream has diminished. ...read more.

Middle

It is because of the small measurement value of magnesium, which is about 0.040g. Thus, the mole of magnesium has percentage error of 2% and 3% respectively in two trials. Percentage errors of other values, like temperature and volume of hydrogen gas, are all below 0.3%. They are so small that have no effect on the final percentage error when added up with percentage error of mole. As a result, the percentage errors of moles of hydrogen gas are exactly the same as the final percentage errors. Two calculated values of molar volume are and . They are both smaller than the acceptable value and have a percentage error of 4.02% and 1.34% respectively. At the beginning, I suppose these systematic errors are due to the dilation of hydrochloric acid. There was a tiny flow of liquid out of the burette and the sunken magnesium fragment produced bubbles. Both are evidences that hydrochloric acid solution in the burette mixed with water in the beaker and the concentration of solution in the burette fell. However, I denied the idea soon because no lump remained in the gauze after the reaction went to the completion. So I suppose the source of systematic errors is the measurement of hydrogen gas produced. In the first trial, I observed many tiny bubbles attached to the gauze during the reaction. ...read more.

Conclusion

These relatively high percentage uncertainties account to the small mass of magnesium. Although the mass is measured by the electronic scale and has a quite small uncertainty of only, the measured value of mass is also quite small, about 0.040g. It makes the percentage uncertainty relatively large. So the slight difference in the mass of magnesium causes the percentage uncertainties to be relatively large. Evaluation To reduce the systematic error to the least extent, the experiment should be improved in several aspects. The magnesium ribbon should not be torn into several small pieces to prevent the falling of magnesium fragment. It would make the calculated result more accurate. To reduce the amount of hydrogen gas dissolved in the solution, I would increase the rate of reaction by using HCl solution of a slightly higher concentration. Then, the time needed to complete the reaction would decrease a lot and the accuracy of the result would be higher as well. Also using the purer and untarnished magnesium ribbon would increase the accuracy. To reduce the random error, the random error of the mole of hydrogen should be reduced mainly. The mole of hydrogen gas produce equals the mole of magnesium in the reaction. The percentage uncertainty of magnesium mass can be reduced by a larger mass of magnesium consumed. Thus, increasing both the mass of magnesium and concentration of hydrochloric acid would increase the precision of the result value. ...read more.

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