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Measuring The Heat Of Two Solutions.

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Measuring The Heat Of Two Solutions Introduction: Chemical and Physical changes involve heat energy. When heat energy is absorbed the change is called endothermic while the release of heat energy is called exothermic. Aim: To dissolve Calcium Chloride and Potassium Nitrate in water while finding the heat of both solutions. Equipment: No more than 12g of Calcium Chloride No more than 12g of Calcium Chloride 2 large cups (preferred polystyrene cups) Electronic balance 100ml measuring cylinder Thermometer Distilled Water Method: 1) Calculate the mass of 0.1 mol of Calcium Chloride (CaCl2) and Potassium Nitrate (KNO3). Ca=40.08 Cl=35.45 K=39.10 N=14.01 O=16.00 Answer: CaCl2= (40.08)+(35.45*2) 1 mole = 110.98. Divide by 10 to get 0.1 mol= 11.098. KNO3=(39.10)+(14.01)+(16.00*3) 1 mole = 101.11. Divide by 10 to get 0.1 mol=10.11. 2) Place the large cup on the balance then add the calculated mass of one substance into the cup. (The calculated mass doesn't have to be exactly 0.1 mol but try to get close). Record in results table. Do the same for other substance using the other large cup. ...read more.


Answer for my results: KNO3= 1st results=100*4.2*7=2940J=2.94KJ 2nd results= 100*4.2*8.5=3570J=3.57KJ 3rd results= 100*4.2*7=2940J=2.94J CaCl2= 1st results= 100*4.2*15=6300J=6.3KJ 2nd results= 100*4.2*14=5880J=5.88KJ 3rd results=100*4.2*15=6300J=6.3KJ 2) Find out the number of moles of each of the substances with both substances. Answer: KNO3 (1) 10.12/101.11=0.10008 mole. (2) 10.09/101.11=0.09979 mole (3) 10.15/101.11=0.10038 mole CaCl2 (1) 11.15/110.98=0.10046 mole (2) 11.11/110.98=0.10010 mole (3) 11.09/110.98=0.09992 mole 3) Calculate the molar heat of the solutions for both measurements (hint: Divide the heat energy calculated by the number of moles) Answer: KNO3= (1) 2.94/0.10008=+29.37KJ/mol (2) 3.57/0.09979=+35.77 KJ/mol (3) 2.94/0.10038=+29.28KJ/mol CaCl2= (1) 6.3/0.10046=-62.71KJ/mol (2) 5.88/0.10010=-58.74KJ/mol (3) 6.3/0.09992=-63.05KJ/mol Discussion: 1) What are the potential hazards and what are the appropriated measures to minimise risk? Make sure that when using a thermometer that you don't stir in a glass container because thermometers are very fragile and it could break inside the glass container. Use polystyrene cups to prevent the thermometer from breaking. Make sure that you are using safety goggles when dealing with substances as some substances can go into your eye and burn it. ...read more.


Eye Contact: Hazard may be either mechanical abrasion or, more serious, burns from heat of hydrolysis and chloride irritation. 2) The real values for KNO3 and CaCl2 are: KNO3=+34.7KJ/mol CaCl2= -90.8KJ/mol Compare these to your results and explain why your results might not be accurate. Also comment on the error of the experiment? Answer: KNO3=(1)= +29.37KJ/mol (2) +35.77 KJ/mol (3) +29.28KJ/mol CaCl2= (1) -62.71KJ/mol (2) -58.74KJ/mol (3) -63.05KJ/mol Answer for my results: My results weren't accurate because I could have used a different chemical compound jar, which makes it more inaccurate. The other jar could have moister which could affect the temperature change. Another error in this experiment is that Potassium nitrate doesn't dissolve properly. It will mean that it might not reach its peak temperature. We also didn't use distilled water, which might cause error. The experiment wasn't insulated enough so there was temperature loss. Another thing is that our measuring instruments and volume instruments weren't that accurate. Another error is that we might of not measured the exact temperature reading. 3) What-dissolving compound was endothermic? Answer: KNO3 Conclusion: That Potassium Nitrate is an endothermic reaction while calcium chloride is an exothermic reaction. ...read more.

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