CHM471 1 - lab report PDF

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FACULTY OF APPLIED SCIENCESLABORATORY REPORTPHYSICAL CHEMISTRY(471)TITLE OF EXPERIMENT CALORIMETRY: HESS’S LAWNO OF EXPERIMENT 1NAME HUSNA INSYIRAH BT SAMADSTUDENT ID NUMBER 2017411714PROGRAMME CODE ASDATE OF EXPERIMENT 12 MARCH 2018DATE OF LAB REPORT SUBMITTED 18 MARCH 2018LECTURER’S NAME MADAM HAI...

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FACULTY OF APPLIED SCIENCES LABORATORY REPORT

PHYSICAL CHEMISTRY (471)

TITLE OF EXPERIMENT NO OF EXPERIMENT NAME STUDENT ID NUMBER PROGRAMME CODE DATE OF EXPERIMENT DATE OF LAB REPORT SUBMITTED LECTURER’S NAME

CALORIMETRY: HESS’S LAW 1 HUSNA INSYIRAH BT SAMAD 2017411714 AS202 12 MARCH 2018 18 MARCH 2018 MADAM HAIRUL AMANI BT ABDUL HAMID

Objectives 1) To compare the heat capacities of a coffee cup calorimeter and a copper calorimeter. 2) To determine the standard enthalpy of formation of magnesium oxide, ∆H°f. Introduction Heat can be defined as the energy transfer from one system to another system because there is differences in the temperature changes of the system and the surroundings. A calorimeter is used tin a chemical reaction to transfer the heat. The calorimeter prevents the loss or gain of heat between the surrounding and the calorimeter itself so that we can measure the amount of heat flow in the system. We can measure the heat of reaction for a given reaction in kilojoules per mole (kJ mol-1) by calculating the values of heat of reaction for other reactions. Hess’s Law states that when reactants are converted to products, the changes in enthalpy has no differences whether there are single or multiple stages or steps of a reaction In this experiment, we are determining the standard enthalpy (heat) of formation of magnesium oxide. Mg(s) + 1/2O2 (g) → MgO (s) Along with all these equations: Mg(s) + 2HCl(aq) → MgCl2(aq) + H2(g) MgO(s) + 2HCl(aq) → MgCl2(aq) + H2O(l) H2(g) + ½O2(g) → H2O(l) The heat of reaction for the reaction between Magnesium with Hydrochloric Acid and the reaction between Magnesium Oxide with Hydrochloric Acid will be obtained experimentally and for the reaction water, the heat of formation can be obtained from the literature. The heat capacity of the calorimeter can be determined by observing the change of temperature when a known weight of hot water is mixed with an amount of cold water in the calorimeter. Apparatus 1. Thermometer (2) 2. Styrofoam cup with cardboard cover lid (2) 3. Copper calorimeter with insulating cover (1) 4. 100cm3 beaker 5. 100cm3 graduated cylinder

Chemicals 1. 2.0M hydrochloric acid 2. Magnesium oxide powder

3. Magnesium powder

Procedure A. Heat capacity of calorimeter The double Styrofoam cups should be in a clean and dry conditions. 1. 50cm3 of tap water was exactly delivered into the calorimeter by using a burette. The cover and the thermometer were replaced. The water temperature was recorded for four minutes at one minute intervals. 2. 50cm3 of hot water (40-50°C above the room temperature) was measured using a graduated cylinder and poured into a beaker. The temperature of the hot water was quickly recorded using another thermometer and completely poured it into the calorimeter (containing cold water) at the fifth minute. The lid was replaced back and the water was carefully stirred with the thermometer. The temperature was recorded every 15 seconds for the next three minutes. 3. Steps 1 and Steps 2 were repeated using the copper calorimeter. B. Reaction 2: Magnesium with Hydrochloric Acid 1. Between 1.0 - 1.1g of magnesium powder was weighed. The exact weigh used was recorded. 2. 50cm3 of 2M HCl was drained from a burette into the calorimeter. The cover and thermometer were replaced. The temperature of the HCl was recorded every minute for four minutes. The magnesium powder was quickly poured into the HCl solution at the fifth minute. The lid was replaced back and the contents in the calorimeter was carefully stirred with thermometer. The temperature was recorded for the next three minutes at 15 seconds intervals. C. Reaction 3: Magnesium oxide with Hydrochloric Acid 1. Between 1.6-1.8g of magnesium oxide was weighed. The exact weight used for MgO was recorded. 2. Step 2 in B was repeated. D. Hydrogen gas with Oxygen gas This value will not be experimentally determined in the laboratory for safety reasons. It has been professionally determined and verified and the value is listed in standard reference sources. The value must be determined in kilojoules per mole (kJ/mol).

RESULT

CALCULATIONS Heat capacity of calorimeter qhot = qcold + qcal Coffee cup calorimeter qhot = mhc(Th -Tf) = (50g)(4.18Jg-1°C-1)(70°C-49°C) = 4389 J qcold = mcc(Tf -Tc) = (50g)(4.18Jg-1°C-1)(49°C-31.5°C) = 3657.5 J qcal = qhot - qcold = 4389 J – 3657.5 J = 731.5 J qcal = Ccal(Tf –Tc) 731.5J = Ccal(49°C-31.5°C) Ccal = 41.8 J°C-1 Copper calorimeter qhot = mhc(Th -Tf) = (50g)(4.18Jg-1°C-1)(70°C-48°C) = 4598 J qcold = mcc(Tf -Tc) = (50g)(4.18Jg-1°C-1)(48°C-32°C) = 3344 J qcal = qhot - qcold = 4598 J – 3344 J = 1254 J qcal = Ccal(Tf –Tc) 1254 J = Ccal(48°C-32°C) Ccal = 78.38 J°-1

Magnesium with Hydrochloric Acid Mg(s) + 2HCl(aq) → MgCl2(aq) + H2(g) No of mole of Mg = mass of Mg molar mass Mg = 1.0038 g 24.3 gmol-1 = 0.0413 mol Mg 1 mol of Mg = 1 mol MgCl2 0.0413 mol Mg = 0.0413 mol MgCl2 Mg is the limiting reactant

No of mole of HCl = MV = (2M)(0.05L) = 0.1 mol HCl

2 mol of HCl = 1 mol of MgCl2 0.1 mol HCl = 0.05 mol MgCl2

Coffee calorimeter ∆T = 80°C - 32°C = 48°C qreaction = qreaction + qcal = mc∆T + C∆T = (50g)(4.18g-1°C-1)(48°C) + (41.8J°C-1) )(48°C) = 12.038 Kj ∆H = 12.038 kJ 0.0413 mol = 291.477 kJ/mol Copper calorimeter ∆T = 63.75°C - 34°C = 29.25°C qreaction = qreaction + qcal = mc∆T + C∆T = (50g)(4.18g-1°C-1)(29.75°C) + (78.38J°C-1)(29.75°C) = 8.550 kJ ∆H = 8.550 kJ 0.0413 mol = 207.02 kJ/mol

Magnesium oxide with Hydrochloric Acid MgO(s) +2HCl(aq) → MgCl2(aq) + H2(l)

No of mole of MgO = mass of MgO molar mass MgO = 1.6055 g 40.3 gmol-1 = 0.0398 mol MgO 1 mol of MgO = 1 mol of MgCl2 0.0398 mol MgO = 0.0398 mol MgCl2 MgO is the limiting reactant

No of mole of HCl = MV = (2M)(0.05L) = 0.1 mol HCl

2 mol of HCl = 1 mol of MgCl2 0.1 mol HCl = 0.05 mol MgCl2

Coffee calorimeter ∆T = 43.5°C – 32.0°C = 11.5°C qreaction = qreaction + qcal = mc∆T + C∆T = (50g)(4.18g-1°C-1)(11.5°C) + (41.8J°C-1)(11.5°C) = 2.884 kJ ∆H = 2.884 kJ 0.0398 mol = 72.362 kJmol-1 Copper calorimeter ∆T = 54.5°C - 34°C = 20.5°C qreaction = qreaction + qcal = mc∆T + C∆T = (50g)(4.18g-1°C-1)(20.5°C) + (78.38J°C-1)(20.5°C) = 5.891 kJ ∆H = 5.891 kJ 0.0398 mol = 148.015 kJ/mol Theoretical Mg(s) + 2HCl(aq) → MgCl2(aq) + H2(g) MgCl2(aq) + H2O(l) → MgO(s) + 2HCl(aq) (reversed) H2(g) + 1/2O2(g) → H2O(l) Mg(s) + 1/2O2(g) → MgO(s)

∆H = -461.96 kJ/mol ∆H = 146.96 kJ/mol ∆H = -285.9 kJ/mol ∆H = -600.9 kJ/mol

Experimental (Coffee cup calorimeter) Mg(s) + 2HCl(aq) → MgCl2(aq) + H2(g) MgCl2(aq) + H2O(l) → MgO(s) + 2HCl(aq) (reversed) H2(g) + 1/2O2(g) → H2O(l) Mg(s) + 1/2O2(g) → MgO(s) Percent yield =

∆H = -291.477 kJ/mol ∆H = 72.362 kJ/mol ∆H = -285.9 kJ/mol ∆H = -505.015 kJ/mol

Actual yield x 100% Theoretical yield = (-505.015 kJ/mol) x 100% (-600.9kJ/mol) = 84.04%

Percent error = Theoretical – Actual x 100% Theoretical = (-600.9kJ/mol)-(-505.015 kJ/mol) (-600.9kJ/mol) = 15.96%

x 100%

Experimental (Copper calorimeter) Mg(s) + 2HCl(aq) → MgCl2(aq) + H2(g) MgCl2(aq) + H2O(l) → MgO(s) + 2HCl(aq) (reversed) H2(g) + 1/2O2(g) → H2O(l) Mg(s) + 1/2O2(g) → MgO(s) Percent yield =

Actual yield x 100% Theoretical yield = (-344.905kJ/mol) x 100% (-600.9kJ/mol) = 57.40%

Percent error = Theoretical – Actual x 100% Theoretical = (-600.9kJ/mol)-(-344.905) x 100% (-600.9kJ/mol) = 42.60%

∆H = -207.02 kJ/mol ∆H = 148.015 kJ/mol ∆H = -285.9 kJ/mol ∆H = -344.905 kJ/mol

DISCUSSIONS In this experiment, we have compared the heat capacities of a coffee cup calorimeter and a copper calorimeter by using the formula, qcal = Ccal(Tf –Tc). The heat capacity of copper calorimeter is 78.38 J°C-1 which is higher than the heat capacity of coffee cup calorimeter, 48.1 J°C-1. This is because the temperature changes of copper calorimeter is smaller than that in coffee cup calorimeter. Based on the formula, q = C∆T, we know that the heat capacity (C) increases when temperature changes (∆T) decreases as ∆T is inversely proportional to C. The percentage error of copper calorimeter is higher than the coffee cup calorimeter. The percentage error of coffee cup calorimeter is 16.92% while the percentage error of copper calorimeter is 42.71%. There are some factors that may affect the results when handling this experiment. The instruments used are very important to be fixed properly. So that it would not affect the value that we calculated. For examples, if the lid of the coffee cup has a hole that can make the heat loss to the surrounding faster than usual. Hence, the value of temperature we get are quite different from the actual. Besides, there will be parallax error when we took the reading of the thermometer as the eyes of the observer are not in the correct position. After that, the temperature recorded may not in line with the time intervals that has been set. To overcome all these errors that may affect the results, the eyes of the observer should be perpendicular to the reading scale of the thermometer. Then, the lid of the coffee cup calorimeter must be in a good condition where there is no hole so that heat could not be escaped. The time read and record the temperature must be estimated correctly with the time intervals so that we could have the correct temperature. The standard enthalpy of formation of coffee cup calorimeter is higher than that of copper calorimeter. The change of temperature in copper calorimeter is higher than that in coffee cup calorimeter because the heat is loss to the surrounding is more in copper calorimeter. Based on the formula q = mc∆T, the heat of reaction ,q increases when the temperature changes, ∆T increases as q is directly proportional to ∆T. The standard enthalpy, ∆H increases when the heat of reaction, q increases as ∆H is directly proportional to q by referring to the formula ∆H = q/n.

CONCLUSIONS 1. The heat capacity of copper calorimeter is higher than the heat capacity of coffee cup calorimeter. 2. The standard enthalpy of formation of magnesium oxide, ∆H°f in coffee cup calorimeter is -72.362 kJmol-1 and standard enthalpy of formation of magnesium oxide, ∆H°f in copper calorimeter is -148.015 kJ/mol.

REFERENCES 1. Arther Adamson (1970). A Textbook of Physical Chemistry, 2th Edition, Academic Press. 2. Shoemaker, D.P. (1989). Experiments in Phisical Chemistry, International Edition. McGraw-Hill. 3. Laidler, Keith (1993). The World of Physical Chemistry, 2th Edition, Oxford University Press. 4. http://faculty.cbu.ca/chowley/chem1104lab/CalorimetryHO.pdf

QUESTIONS 1. a) Which of the two calorimeters: coffee cup calorimeter or copper calorimeter has s higher heat capacity? Copper calorimeter b) What conclusion can you make regarding the relationship of heat capacity of calorimeter with temperature change of the reactions? ↑q = C∆T↓. The heat capacity of calorimeter increases when the temperature change of the reactions decreases. 2. For the following problems, assume that the volume of the final solution is 200cm3, the density of the solution is 1.00gmL-1 and the specific heat capacity of the solution is the same as the water (4.184Jg-1°C) . a) When 0.800g of Ca metal is added to 200cm3 of 0.500 M HCl(aq) according to the method described in Procedure B, a temperature increase of 13.0°C is observed. What is ∆Hrxn at room temperature of the reaction Ca(s) + 2H+ (aq)? Ca(s) + 2HCl(aq) → CaCl2(aq) + H2(g) No of mole of Ca = mass of Ca No of mole of HCl = MV molar mass Ca = (0.500M)(0.20L) = 0.800 g = 0.1000 mol HCl 40.078gmol-1 = 0.0200 mol Ca 1 mol of Ca = 1 mol of CaCl2 2 mol of HCl = 1 mol of MgCl 0.0200 mol Ca = 0.0200 mol CaCl2 0.1000 mol HCl = 0.0500 mol MgCl2 Ca is the limiting reactant ∆T = 13.0°C qreaction = mc∆T = (200g)(4.18g-1°C-1)(13.0°C) = 10.868 kJ ∆Hrxn = 10.868 kJ 0.0200 mol = -543.40 kJ/mol

b) When 1.12g of CaO is added to 200cm3 of 0.500 M HCl(aq) according to the method described in Procedure B, a temperature increase of 4.62°C is observed. What is ∆Hrxn at room temperature of the reaction CaO(s) + 2H+ (aq)? CaO(s) + 2HCl(aq) → CaCl2(aq) + H2O(g) No of mole of CaO = mass of CaO No of mole of HCl = MV molar mass CaO = (0.500M)(0.20L) = 1.12 g = 0.1000 mol HCl 56.08gmol-1 = 0.0294 mol CaO 1 mol of CaO = 1 mol of CaCl2 0.0294 mol CaO = 0.0294 mol CaCl2 CaO is the limiting reactant

2 mol of HCl = 1 mol of CaCl 0.1000 mol HCl = 0.0500 mol CaCl2

∆T = 4.62°C qreaction = mc∆T = (200g)(4.18g-1°C-1)(4.62°C) =3.862 kJ ∆Hrxn = 3.862 kJ 0.0294 mol = -131.36 kJ/mol

3. A student carelessly inserts the thermometer while assembling the coffee cup calorimeter and a large hole is torn in the plastid lid. How will this affect his experimental results? The heat of water will loss to the surrounding through the large hole. Hence, it will affect the temperature of hot water to be decreased faster than usual. Thus, the temperature change will be increased....