Lab Report 8: Determination of the Heat of Dissolution of a Salt PDF

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####### Formal Lab Report Rubric A1Student Name: ____Experiment Title: __Abstract Question asked & results • Incomplete • Missing Introduction Satisfactory: Objectives stated, Essential concepts complete, Prediction Unsatisfactory: Objectives stated, Essential concepts complete, Prediction Missi...

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Formal Lab Report Rubric

A.Fortier

Azizah Hossain Student Name: ________________________________ Determination of the Heat of Dissolution of a Salt

Experiment Title: __________________________________________ Abstract •

Question asked & results

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Missing

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Unsatisfactory: Objectives stated, Essential concepts complete, Prediction

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Missing components: Objectives stated, Essential concepts complete, Prediction

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Procedure not submitted

Introduction •

Satisfactory: Objectives stated, Essential concepts complete, Prediction

Procedure •

Signed procedure included

Data and Results Scientific Integrity • Neat and legible • Errors are crossed out with one strike and rewritten neatly Significant Figures & Units • Correct units are used • Correct S.F. representing glassware and equipment used

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Penmanship can be improved Errors are scribbled

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Messy Use of pencil

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Few errors on units Few S.F. errors representing glassware and equipment used

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Many errors on units Many S.F. errors representing glassware and equipment used

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Lacking accuracy and/or precision Not all data shown

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Poor accuracy and/or precision Missing a significant amount of data

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Unsatisfactory: Title, Axes labeled & units, Data points, Best fit curve or line, Equation of the line

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Missing components: Title, Axes labeled & units, Data points, Best fit curve or line, Equation of the line

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Numbered as per lab manual Has titles describing work Formula may be shown Some incorrect answers

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Not numbered as per lab manual Lack of titles describing work Formula may not be shown

Data • •

Accurate and precise All data shown

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Graphs (if applicable) •

Satisfactory: Title, Axes labeled & units, Data points, Best fit curve or line, Equation of the line

Sample Calculations • • • •

Numbered as per lab manual Has titles describing work Formula is shown Correct answers

Questions (pre lab and/or post lab questions): Only randomly selected questions will be graded • •

Selected question(s) is/are correctly answered All questions have been answered

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Selected question(s) is/are correctly answered Not all questions have been answered

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Selected question(s) is/are incorrect Not all questions have been answered

Discussion •

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Missing components: Analysis & Discussion of results

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Has some references (1-2) Improper formatting

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Has required references (2-3) Proper format

Every student has to submit their own lab report. At the end of every laboratory session, make sure your instructor signs your data sheet. Reports must be typed (calculations also). You will be graded based on significant figures and units Marks will be deducted if this format is not respected (follow presentation order from template) Each section must be on a separate page and have a proper title (same as rubric grid) Use this page as your title page and template for your lab report. Report must be in font times or times new roman and size 11 or 12.

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Abstract In this experiment, we aim to learn the process on how to determine the heat acquired when dissolving a salt in calorimetry. Ultimately, the goal is to address the molar heat of the sample in question and to assemble the material needed to partake in this experiment. When a salt is dissolved in water, it can heat the solution up or cool it down. Therefore, making the enthalpy of the solution negative (heat generating) or positive (heat absorbing). After further demonstrations, this experiment is deemed to be an endothermic reaction where heat is absorbed from its surroundings. In general, we can conclude that on both trials, the molar enthalpy was positive.

Experiment 8: Determination of the Heat of Dissolution of a Salt

Introduction “Heat is the amount of thermal energy contained in a substance and is a form of kinetic energy due to the motions of molecules. The amount of heat absorbed or released by a physical or chemical process can be measured using a technique called calorimetry. A simple calorimeter can be constructed using two styrofoam cups with a lid. In the calorimeter, heat is transferred to or from a known mass of water by the process, which in this case, is the dissolution of a salt. The amount of heat absorbed or released by water can be calculated by the following formula:

where; q = heat absorbed or released (Joules/J) m = mass of the water/solution in the calorimeter (grams/g) s = specific heat capacity of water (4.184 j/g °c)

Objective To measure the heat capacity of the sample in question and to determine whether the process was endothermic or endothermic using calorimetry.

Hypothesis I had presumed that the temperature would increase when dissolving the NH4Cl resulting in a negative molar enthalpy.

Material used - 2 Empty coffee cups - Lid - Beaker - Distilled water - Graduated cylinder - Foam - Styrofoam - Stirrer - Thermometer - NH4Cl salt

Sample Calculations

9. Moles of NH4Cl Trial 1 Mass of NH4Cl: 4.9866 g Molar mass of NH4Cl: 53.492 g/mol 4.9866 g. NH4Cl x 1 mol / 53.492 g = 0.093221 mol NH4Cl Trial 2 Mass of NH4Cl: 5.3622 g Molar mass of NH4Cl: 53.492 g/mol 5.3622 g. NH4Cl x 1 mol / 53.492 g = 0.10024 mol NH4Cl 10. Heat of Dissolution (kJ) Trial 1

q = (4.9866 g) x (4.184 j/g °c)(7 °C) q = 146.0 kJ Trial 2

q = (5.3622 g) x (4.184 j/g °c)(7 °C) q = 157.0 kJ 11. Molar enthalpy of Dissolution (kJ/mol^-1) Trial 1 =q/n = 146.0 / 0.093221 x 1000 = 1.566 kJ/mol Trial 2 =q/n = 157.0 / 0.10024 x 1000 = 1.566 kJ/mol 12. Average molar enthalpy of Dissolution (kJ/mol^-1) Average molar enthalpy of Dissolution = 1.566 + 1.566 / 2 = 3.132 / 2 = 1.566 kj/mol

Pre-lab questions 1. Mass of water = density x volume = 1 g/ml x 2.548 L x 1000 ml/L Specific heat capacity of water = 4.18 j/g^-1°c^-1

= 22.5 - 18.1 = 4.4 °C q = 2548 x 4.18 x 4.4 q = 46862.816 J ~ 47 J —> heat gain by water q’ = heat loss by metal q’ = (m) metal x 0.745 x 76.9 °C (95 - 18.1) now heat loss = heat gain (m) metal x 0.745 x 76.9 = 46862.816 (m) metal = 46862.816 / 0.745 x 76.9 = 817.9858 g ~ 818 g

Post-lab questions 1. If our calorimeter was not properly insulated then some amount of heat will escape into the surroundings therefore the salt will get less amount of heat. Hence, the formula for heat gained = change in internal energy will no longer be valid as some heat will be gone because it will escape into the surroundings. This will lead to an excess in our calculation because of heat loss net heat gained will be less which will cause too large excess in our calculation.

2. The purpose of a lid on the coffee cup is that it also reduces the amount of heat exchange between the water and the surrounding air. So if my partner forgot to cover the lid while monitoring the temperature, the air from the surroundings would enter the coffee cup which will increase the amount of heat and give an incorrect temperature calculation.

Discussion Throughout the course of the lab, we utilized calorimetry to determine the molar enthalpy of approximately 5 grams of NH4Cl. The determination of the heat of dissolution of the salt involved assembling a calorimeter and the addition of deionized water then proceeding to record the mass each time. Finally, stirring in the salt and monitoring the temperature to record any changes. Through the usage of stoichiometry and specific heat capacity formula, we were able to determine the moles contained in each sample, the heat of dissolution and the molar and average enthalpy of dissolution. For trial 1, the mass of NH4Cl was 4.9866 g and the moles calculated resulted to 0.093221 mol, the heat of dissolution was 146.0 kJ. For trial 2, the mass of NH4Cl was 5.3622 g and the moles calculated were 0.10024 mol. For both trials, the temperature dropped from 16 degrees Celsius to 9 degrees Celsius and they contained the same molar enthalpy of dissolution which was 1.566 kJ/mol. Therefore, our average enthalpy of dissolution for NH4Cl was also 1.566 kJ/mol. There was no standard deviation specified for our two trials therefore there is no way of telling if our values were precise or not. Thus, the percent error may be small or large so it cannot be concluded if the results found were accurate.

References Zumdahl, Introductory Chemistry, 2nd Custom Edition, Nelson Education Ltd., 2017 Laboratory Manual for Remedial Activities for Secondary V Chemistry, Dawson College., (202-001-RE) “7:3: Heats of Reactions and Calorimetry” https://chem.libretexts.org/Bookshelves/General_Chemistry/Map%3A_General_Chemistry_(Petrucci_et_al.)/ 07%3A_Thermochemistry/7.3%3A_Heats_of_Reactions_and_Calorimetry “5.2: Calorimetry” https://opentextbc.ca/chemistry/chapter/5-2-calorimetry/ “Experiment 7: Heat of Solution of a Salt” https://www.laguardia.edu/uploadedfiles/main_site/content/academics/departments/natural_sciences/docs/ scc205-heat-of-solution-of-a-salt.pdf...