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Analysing; Enthalpy of Decomposition of Sodium Hydrogencarbonate

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Introduction

Skill 3: Analysing; Enthalpy of Decomposition of Sodium Hydrogencarbonate Procedures and results Sodium Carbonate experiments Chemical Mass of Cup (grams) Mass of solid + cup (grams) Mass of solid (grams) Na2CO3 1.041 3.541 2.500 Na2CO3 1.114 3.514 2.500 Na2CO3 0.935 3.435 2.500 Table of results Time Experiment 1 Experiment 2 Experiment 3 Temp. of solid (0C) Temp. of solution (0C) Temp. of solid (0C) Temp. of solution (0C) Temp. of solid (0C) Temp. of solution (0C) 0 21.2 21.0 21.2 20.0 21.2 20.0 1 - 21.0 - 20.0 - 20.0 2 - 21.0 - 20.0 - 20.0 3 - 21.0 - 20.0 - 20.0 4 - - - - - - 5 - 25.5 - 25.0 - 25.0 6 - 25.0 - 24.4 - 24.0 7 - 24.8 - 24.2 - 24.0 8 - 24.6 - 24.0 - 23.8 9 - 24.5 - 24.0 - 23.8 10 - 24.5 - 23.9 - 23.6 Analysis Mr. of Sodium Carbonate = 2 x Ar (Sodium) + Ar (Carbon) + 3xAr (Oxygen) = 2 x 23.0 + 12.0 + 3 x 16.0 = 106 Moles of sodium carbonate used = mass of solid used Mr = 2.500/106 = 0.0235 mol Mass of acid = volume x density = 30.00 x 1 = 30.0 grams Mass of Solution = mass of acid + mass of solid = 30.0 + 2.500 = 32.5 grams The same amount of acid and solution was used throughout the 3 experiments Experiment 1 (T = T2 - T1 = 25.61 - 21.0 = 4.6 0C Energy transferred to surrounding = m x c x (T ...read more.

Middle

Maximum error of reading an apparatus = maximum error x 100 Amount read Maximum error of balance = 0.1/(the "difference" of 2 measurements) x 100 = 0.1/(1.0) x 100 = 10.0 % As per worksheet. However, in reality we used a more accurate balance that reads to 0.0001, thus, the reality maximum error of balance = 0.0001/1.0 x 100 = 0.01% Maximum error of burette = 0.15/30 x 100 = 0.50 % Maximum error of thermometer = 0.1/(the "difference" of 2 measurements) = 0.1/(24.5-13.8) = 0.93 % Maximum error from apparatus reading = sum of maximum errors = 10.0 % + 0.50% + 0.93% = 11.43 % There are other possible unquantified errors that could have interfered with the reaction; one main one would be heat loss. Heat loss cannot be quantified, as cannot be the methods in which the graphs were extrapolated, thus reduces the inaccuracies of this experiment. There could have also been substances, in particular solids that were left in the washing cup, despite the fact that I tried to use all the solid and use the "wash" the cup with some acid that I had previously extracted from the given amount of 30.00 ml. Skill 4: Evaluation; Enthalpy of Decomposition of Sodium Hydrogencarbonate Look at your graphs and comment on your results. Are you lines of best fit good enough for you to extrapolate the confidence? Are there any anomalous results? Suggest 1 possible reason for your anomalous result even if your results are within tolerance! ...read more.

Conclusion

Also, as I measured 2 things, different thermometer gives out different results, thus it was hard to determine whether the temperature difference would be acceptable. It could be avoided by using the same temperature, but not forgetting to wipe the acid or bases off (wash and clean the thermometer before measuring another chemical). The timescale of that was involved could have also been misleading, we recorded the temperature every minute, while the reaction could have occurred for a scale of, probably 15-20 seconds, thus, it would probably be better if we had recorded the temperature at a shorter time scale difference, over a longer period. Because the timescale we used may have bee too short, and maybe by using a longer time span, for example, 15 minutes, we could have mead the patterns and trends of the cooling curve more apparent. There could have also been substances, in particular solids that were left in the washing cup, despite the fact that I tried to use all the solid and use the "wash" the cup with some acid that I had previously extracted from the given amount of 30.00 ml. A way of avoiding this is to ensure that the weighing cup is properly rinsed with the acid, and that the entire solid is included in the reaction mixture. Other ways of improving this experiment would include the use of a pipette instead of a burette to measure out the acid, as it gives off a more accurate reading. Using a higher concentration of both acids and bases, to ensure reaction to occur, and the use of more standard conditions in the lab. 1 Estimated using regression line equation- see appendix A ...read more.

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