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Experiment on looking at enthalpy of solutions

Extracts from this document...

Introduction

Experiment looking at enthalpy of solutions Aim: To find the enthalpy change of certain solutions (Ammonium chloride with water, and Iron Chloride with water) under a 1:100 ratio (solute: solvent) and derive conclusions and evaluations after the experiment. Materials: * 1 Data Logger * 10.8g of NH4Cl (Ammonium Chloride) * 456 ml of distilled water * 3.2 g of FeCl3 (Iron(iii)Chloride) * 2 big beakers * 1 electronic thermometer that can be adapted to the data logger * 1 memory stick * 1 glass stirrer * 1 electronic balance * 1 spoon * 2 sheets of paper Method: Part A 1. Fix the data logger so that it records for a time of 300s, with 1 sample per second. 2. Connect the thermometer to the data logger, and have it fixed, ready to use. 3. Place in one beaker (clean and dry) 180 ml of distilled water. Put the electronic thermometer inside the beaker and start recording for 120 seconds. 4. Weigh 5.4g of ammonium chloride, and place it in the beaker with the distilled water after the 120 seconds are recorded. Stir and leave it for 180 seconds. Save your results, organize them in the pc, and produce a graph of temperature against time. 5. Repeat steps 2-4 and produce an average temperature for this solution, as well as a graph of time against average temperature. Make sure to clean and dry the beaker prior to repeating the experiment; this way the test will be fair. 6. From the average temperature, determine ?T (numerical difference before/after the addition of the solute), and do the process for calculating the enthalpy change. Part B 1. Now, take a clean and dry beaker, and place 48ml of distilled water inside. Put the electronic thermometer inside and start recording with the data logger, for a period of 120 seconds. 2. After that period of time, weigh and place 1.6 g of Iron Chloride inside the beaker. Stir it well, and leave it for 180 seconds more. ...read more.

Middle

267,00 15,10 15,20 15,15 268,00 15,10 15,20 15,15 269,00 15,10 15,20 15,15 270,00 15,20 15,20 15,20 271,00 15,20 15,20 15,20 272,00 15,20 15,20 15,20 273,00 15,20 15,20 15,20 274,00 15,30 15,20 15,25 275,00 15,30 15,20 15,25 276,00 15,30 15,20 15,25 277,00 15,30 15,20 15,25 278,00 15,30 15,20 15,25 279,00 15,30 15,20 15,25 280,00 15,30 15,20 15,25 281,00 15,30 15,20 15,25 282,00 15,30 15,20 15,25 283,00 15,30 15,20 15,25 284,00 15,30 15,20 15,25 285,00 15,30 15,20 15,25 286,00 15,30 15,20 15,25 287,00 15,30 15,20 15,25 288,00 15,30 15,20 15,25 289,00 15,20 15,20 15,20 290,00 15,20 15,20 15,20 291,00 15,30 15,20 15,25 292,00 15,20 15,20 15,20 293,00 15,20 15,20 15,20 294,00 15,20 15,30 15,25 295,00 15,20 15,30 15,25 296,00 15,20 15,20 15,20 297,00 15,20 15,20 15,20 298,00 15,20 15,20 15,20 299,00 15,20 15,20 15,20 300,00 15,20 15,20 15,20 Part 2: Looking at enthalpy change between Iron (iii) and distilled water, with a ratio equivalent to 1:100 Calculating enthalpy change for FeCl3+H2O= FeCl3(aq, 100 H2O) Ratio: (1.6/162.5):(48/18) Ratio: 0.027:2.7 Q=MC?T Q=(48/1000)*4.2*4.3 Q=0.048*4.2*4.3 Q=0.87 Kj ?H= 0.87*1/0.027 ?H=32.2 kj/mol Time (s) Temperature 1(C) temperature 2(C) Average Temperature(C) Max Temp.(C) Min.Temp(C) ?T 0,00 17,40 17,50 17,45 21,65 17,35 4,30 1,00 17,30 17,40 17,35 2,00 17,30 17,40 17,35 3,00 17,30 17,40 17,35 4,00 17,30 17,40 17,35 5,00 17,30 17,40 17,35 6,00 17,30 17,40 17,35 7,00 17,30 17,40 17,35 8,00 17,30 17,40 17,35 9,00 17,30 17,40 17,35 10,00 17,30 17,40 17,35 11,00 17,30 17,40 17,35 12,00 17,40 17,50 17,45 13,00 17,40 17,50 17,45 14,00 17,40 17,50 17,45 15,00 17,40 17,50 17,45 16,00 17,40 17,50 17,45 17,00 17,40 17,50 17,45 18,00 17,40 17,50 17,45 19,00 17,50 17,60 17,55 20,00 17,50 17,60 17,55 21,00 17,50 17,60 17,55 22,00 17,50 17,60 17,55 23,00 17,50 17,60 17,55 24,00 17,60 17,70 17,65 25,00 17,60 17,70 17,65 26,00 17,60 17,70 17,65 27,00 17,60 17,70 17,65 28,00 17,60 17,70 17,65 29,00 17,60 17,70 17,65 30,00 17,60 17,70 17,65 31,00 17,60 17,70 17,65 32,00 17,60 17,70 17,65 33,00 17,60 17,70 17,65 34,00 17,60 17,70 17,65 35,00 17,70 17,80 17,75 ...read more.

Conclusion

An aspect that should be carefully seen is the mass of substances. Some groups did not use electronic scales, and used manual scales; that means that the normal error is greater. The electronic scale has an error of � 0.01, while the electronic scale has an initial �0.1 plus usual human mistakes or laziness for precision. When calculating the enthalpy change for iron chloride, there was a small uncertainty as the ratio of the solute did not match the solvent one. In those cases, the most reliable thing to do is divide the number of moles of the solvent by 100 and follow what the theoretical procedure says. The possible cause for this could have been an imprecision when measuring quantities, therefore those mistakes appeared. Evaluation Although one could say that electronic measurements are accurate, it was evidenced that between trials, differences were noticed. Therefore, it is best to do more than two in order to obtain the best average possible. One discrepancy noticed, was the measuring of liquids. These were not measured by electronic means, while the powders were. This means that measurements can slightly change, as one measuring instrument is manual and one is electronic. This makes that the experiment looses its fairness, and thus the experiment will not be correctly done. For future occasions, it is best to measure all with electronic instruments, preferable of the same brand so that the error margins reduce. Further, in order to have a proper reading of the graphs, all solutes should be inserted into the solvent at 120 seconds. Some groups did not care about this issue. This is an important step, as results can be easily seen, and secondly because if the experiment wants to be fair, all substances should be left with the same time for reaction. Some groups poured the solute at 135 seconds, because they were not ready; this made the experiment a bit inaccurate. For future occasions, it is best to have everything in hand 10 seconds prior to the 120 seconds margin, and thus the laboratory will increase its accuracy. ?? ?? ?? ?? -1- ...read more.

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