Measuring The Heat Of Two Solutions Essays

Measuring The Heat Of Two Solutions Essays Measuring The Heat Of Two Solutions Essay Measuring The Heat Of Two Solutions Essay 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 doesnt 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. 3) Add exactly 100ml of the distilled water to the measuring cylinder and record its temperature. 4) Add the water to the large cup and stir with the thermometer until substance has dissolved. Record temperature. 5) Clean and dry large cups and repeat process for both substances and put in results table. Results: Results table (numbers that are in the table are my results) Potassium Nitrate Calcium Chloride Mass of solid dissolved 10.12 11.15 Mass of 100ml of water 100g 100g Initial Temp (C) 12C 12C Final Temperature (C) 5C 27C Temperature change 7C 15C 2nd Measurements Mass of solid dissolved 10.09 11.11 Mass of 100ml of water 100g 100g Initial Temp (C) 12C 13C Final Temperature (C) 3 1/2 C 27C Temperature change 8 1/2 C 14C 3rd Measurements Mass of solid dissolved 10.15 11.09 Mass of 100ml of water 100g 100g Initial Temp (C) 12C 12C Final Temperature (C) 5C 27C Temperature change 7C 15C Results (Calculations): 1) Calculate the heat absorbed or released for each substance, in Joules and kilojoules using the formula: Heat energy= mass of water * specific heat capacity * temperature change. (Note that the specific heat capacity for water is 4.2Jg-1 K-1) 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 dont 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. For Potassium nitrate: Inhalation: Causes irritation to the respiratory tract. Symptoms may include coughing, shortness of breath. Ingestion: Causes irritation to the gastrointestinal tract. Symptoms may include nausea, vomiting and diarrhea. May cause gastroenteritis and abdominal pains. Purging and diuresis can be expected. Rare cases of nitrates being converted to the more toxic nitrites have been reported, mostly with infants. Skin Contact: Causes irritation to skin. Symptoms include redness, itching, and pain. Eye Contact: Causes irritation, redness, and pain. Chronic Exposure: Under some circumstances methemoglobinemia occurs in individuals when the nitrate is converted by bacteria in the stomach to nitrite. Nausea, vomiting, dizziness, rapid heart beat, irregular breathing, convulsions, coma, and death can occur should this conversion take place. Chronic exposure to nitrites may cause anemia and adverse effects to kidney. Potential Hazards for Calcium Chloride: Inhalation: Granular material does not pose a significant inhalation hazard, but inhalation of dust may cause irritation to the respiratory tract, with symptoms of coughing and shortness of breath. Ingestion: Low toxicity material but ingestion may cause serious irritation of the mucous membrane due to heat of hydrolysis. Large amounts can cause gastrointestinal upset, vomiting, abdominal pain. Skin Contact: Solid may cause mild irritation on dry skin; strong solutions or solid in contact with moist skin may cause severe irritation, even burns. 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 werent 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 doesnt dissolve properly. It will mean that it might not reach its peak temperature. We also didnt use distilled water, which might cause error. The experiment wasnt insulated enough so there was temperature loss. Another thing is that our measuring instruments and volume instruments werent 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.