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Thermal Decomposition of Calcium Carbonate

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Introduction Calcium Carbonate, CaCO3 decomposes with heat, to produce Calcium Oxide, CaO and Carbon Dioxide, CO2. CaCO3(s) CaO(s) + CO2(g) The object of this practical exercise is to determine the enthalpy change for this reaction by an indirect method based on Hess' Law. Results Table Experiment 1: Mass of CaCO3 and weighing bottle 3.47g Mass of empty weighing bottle 1.08g Mass of CaCO3 used 2.39g Temperature of acid initially 22oC Temperature of solution after mixing 24oC Temperature change during reaction 2oC Experiment 2: Mass of CaO and weighing bottle 2.58g Mass of empty weighing bottle 1.00g Mass of CaO used 1.58g Temperature of acid initially 22oC Temperature of solution after mixing 27oC Temperature change during reaction 5oC Calculating the Enthalpy Change Experiment 1: Calculating the H1 for the reaction between CaCO3 and HCl Using the formula: Density = Mass Volume , We can work out the mass of liquid (HCl) Mass = Density x volume = 2.0 x 0.05 = 0.1 grams Using the calculated mass, we can work out the total energy transfer using the formula: Energy Transfer = Mass of Liquid x specific heat capacity x change in temperature = 0.1 x 4.2 x (24-22) = - 0.84 J From the results table, we can see that the temperature increased from 22oC to 24oC, so we can deduce that the reaction was EXOTHERMIC. ...read more.


However, after looking over my method, I can see a few minor errors that could have altered the results given. In the experiment, one or two minor misjudgements could have been made; although such mistakes will not have been sufficient enough to change the results. The top pan balance, used for weighing out the calcium carbonate and calcium oxide, is a very accurate method of measuring quantities. However, top pan balances only measure to two decimal places. On a balance like this the second decimal place is not reliable, giving an error of �0.01g. CaCO3 (0.01/2.39) x 100 = 0.42%% chance of error CaO (0.01/ 1.58) x 100 = 0.63%% chance of error. To overcome this problem, it is important to weigh out the solids to the required weigh; take them off the scale; place them back on the scale and check the weight. If the two weights are very different from each other, it may be best to weigh the solids again. However the calculated chances of errors are not high enough to cause any concern for the accuracy of my results. One of the major concerns about the accuracy of my results was the ability of the thermometer to read the temperature to the required level. ...read more.


This, in turn, will distort the calculated enthalpy changes, and they will be incorrect. It is known that beakers can be not be very accurate, as the measurements are in 50cm3 graduations; I decided to use a measuring cylinder to measure the acid, which range from 0cm3 to 250cm3, with 1.0cm3 graduations. Therefore the measurements of volume will be rounded to the nearest 1.0cm3, giving a degree of inaccuracy. When measuring the acid out, I need to make sure the meniscus is at the bottom of the measurement line. All these four errors are significant to the experiment, as they can all contribute to an increase or decrease of the temperature of the experiment. The most significant error in the method was the fact that the temperature is not correctly identified by the thermometer. I believe this to be the most important factor, as this is the main way of detecting the temperature. If the temperature is slightly out, the end result will be slightly out. Overall I think that experiment 1; involving CaCO3 was the more reliable of the two experiments. The main reason behind this decision was the fact that the reaction is very quick, leaving less time for any heat to be lost to the environment and its surroundings. ?? ?? ?? ?? Chemistry Coursework - Assessed Practical ...read more.

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