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Abby Weitkamp Honors/AP Chemistry Hays 22 November 2016 Designing a Hand Warmer Lab Purpose Statement
The purpose of this lab is to investigate the energy changes accompanying the formation of solutions for common laboratory salts, and then apply the results to design a hand warmer wa rmer that is reliable, safe, and inexpensive. Partners
● Sana Navaid ● Madeline Crowley ● Michelle Shumiatsky Introduction
1. When When chro chromi mium um chlo chlori ride, de, CrC CrCll2, is dissolved in water, the temperature of the water increases. (a) Is the heat of solution exothermic or endothermic? (b) Which is stronger-the attractive forces between water molecules and chromium an d chloride ions, or the combined ionic bond strength of CrCl2 and intermolecular forces between water molecules? Explain. a. The heat of the soluti solution on is endother endothermic mic because because it is cold cold to the touch touch and is is taking in heat.
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b. The bond of the chromium chloride is stronger because it contains intramolecular forces and the separate ions contain intermolecular forces which are not as strong. 2. A solution solution was formed formed by combining combining 25.0 25.0 g of solid solid A with 60.0 60.0 mL of distilled distilled water, water, with the water initially at 21.4℃. The final temperature of the solution was 25.3℃. Calculate the heat released as the solid dissolved, qsoln, assuming no heat loss to the calorimeter (see Equation 1).
3. In Question Question 2 above, above, the the calorimeter calorimeter was found found to have have a heat capacit capacity y of 8.20J/ 8.20J/℃. If a correction is included to account for the heat absorbed by the calorimeter, what is the heat of solution, qsoln?
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4. The solid solid in in Questio Question n 2 was alumin aluminum um sulfat sulfate. e. Al2(SO4)3. Calculate the molar heat of solution, ΔHsoln, for aluminum sulfate. Hint: The units for molar heat of solution are kilojoules per mole (KJ/mole). First determine the heat released per gram of solid.
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Materials
● Magnesium sulfate, anhydrous, MgSO4, 5g ● Distilled water ● Lithium chloride, LiCl, 10g ● 2 nested polystyrene cups
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Equipment
● Beaker, 250-mL ● Graduated cylinder, 100-mL ● Heat-resistant gloves ● Hot plate ● Magnetic stirrer ● Stirring bar ● Support stand ● Ring clamp ● Digital thermometer ● Timer Procedure
Part A. Heat Capacity of the Calorimeter
1. Place the two two nested nested cups in a ring ring clamp that that is attached attached to the the support support stand. 2. Place a magnetic magnetic stirre stirrerr below the the calorimeter, calorimeter, then then lower lower the ring ring clamp so the the bottom bottom of the cup is almost touching the stirrer. 3. Measure Measure 100.0 mL of water water in a 100100- mL graduated graduated cylinder cylinder and move move the water water to the calorimeter. 4. Place a stirri stirring ng bar between between the nested nested cups and and set the bar bar slowly slowly spinning. spinning. 5. Measure Measure and record record the the initial initial temperature temperature of the the water. water. 6. Heat approxim approximately ately 125 mL of distill distilled ed water water to about 70 70℃ in a 250- mL beaker.
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7. Measure Measure 100.0 mL mL of the the heated water water in in a 100- mL mL graduated graduated cylinder cylinder using using heat heat resistant gloves. 8. Measure Measure and record record the temperature temperature of the the hot water. 9. Pour the the hot water into the water water in the the calorime calorimeter. ter. 10. Insert the thermometer and stir the the water 11. Record the mixing mixing temperatur temperaturee Tmix after 20 seconds. 12. Empty and dry the the calorimeter. calorimeter. 13. Calculate Calculate the calorimeter calorimeter constant. Part B. Calorimetry Procedure
1. Measure Measure 45.0 mL of distil distilled led water water in a 100- mL graduated graduated cylinde cylinderr and transfer transfer it it to the calorimeter 2. Measure Measure and record record the the initial initial temperature temperature of the the water. water. 3. Measure Measure 5.00 g of of anhydrous anhydrous magnesium magnesium sulfate sulfate in a weighin weighing g dish. 4. Put a stir stir bar into the the calorimeter calorimeter and slowly slowly stir stir the water. 5. Add the anhydrous anhydrous magnesi magnesium um sulfate sulfate to the calori calorimeter meter and and insert the thermomet thermometer. er. 6. Record Record the the highes highestt temper temperatu ature re readi reading. ng. 7. Calcul Calculat atee the the mola molarr heat heat.. Part C. Guided Inquiry Calorimetry Procedure.
1. Measure Measure 40.0 mL of distil distilled led water water in a 100- mL graduated graduated cylinde cylinderr and transfer transfer it it to the calorimeter 2. Measure Measure and record record the the initial initial temperature temperature of the the water. water. 3. Measure Measure 10.00 10.00 g of lithium lithium chloride chloride in in a weighi weighing ng dish. dish.
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4. Put a stir stir bar into the the calorimeter calorimeter and slowly slowly stir stir the water. 5. Add the lithium lithium chlorid chloridee to the calorimet calorimeter er and insert insert the thermom thermometer. eter. 6. Record Record the the highes highestt temper temperatu ature re readi reading. ng. 7. Calcul Calculat atee the the mola molarr heat heat.. Data and Calculations
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Observations
● Part A
ad ded to the initial room temperature water, the Tmix ○ When the heated water was added temperature rose compared to the initial and dropped compared to the heated. ○ The Tmix was 42.5℃ ● Part B ○ The highest temperature was 53.1℃ ○ The ΔT was 26.7℃
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○ The solute did not completely dissolve ● Part C ○ The highest temperature was 41.9℃ ○ The ΔT was 19℃ Conclusion
Lab Questions
1. Review the the calorimetr calorimetry y procedure procedure and answer answer the followin following g questions: questions: a. What data is is needed needed to calculat calculatee the enthalp enthalpy y change change for a reaction? reaction? i.
The temp tempera eratur turee of the reacta reactants nts sub subtra tracte cted d from from that that of the the produc products ts is is needed to calculate the enthalpy change for a reaction.
b. Identify the variables that will influence the experimental data. i.
The variabl variables es that that will will influen influence ce the experim experiment ental al data data are: are: 1. Temper Temperat atur uree of of wat water er 2. Water ma mass 3. Temper Temperat atur uree of of sol solut utee 4. Sol Solute ute mass mass
c. What variabl variables es should should be controll controlled ed (kept constant) constant) during during the the procedure? procedure? i.
The variabl variables es that that sho should uld be cont control rolled led during during the proced procedure ure are: are: 1. Init Initia iall temp temper erat atur uree 2. Mass Mass of water water (conce (concentr ntrati ation on can be change changed) d) 3. Am Amou ount nt of of stir stirri ring ng
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d. The independent independent variable variable in an experiment experiment is is the variable variable that is is changed changed by the experimenter, while the dependent variable responds to or depends on the changes in the independent variable. Name the independent and dependent variables in a calorimetry experiment to determine the molar heat of solution. i. ii.
Thee inde Th indepe pende ndent nt vari variabl ablee is is mas masss of of the the sol solut ute. e. The depe dependen ndentt variab variable le is is the the ΔT because because the concent concentrat ration ion of of the the solut solution ion can change and, therefore, cause the temperature to change.
e. Discuss Discuss the factors factors that that will will affect the precision precision of the the experimental experimental results. results. i.
The fact factors ors that that will will affec affectt the precis precision ion of of the the experi experimen mental tal resu results lts are: are: 1. Mass of of solutesolute- too too much or too little little will will cause cause differen differentt results results 2. Initial Initial temperatu temperaturere- if incorrect, incorrect, entire entire answer answer will will be wrong 3. Mix temperat temperatureure- if if incorrect incorrect,, entire entire answer answer will will be wrong
2. LiCl makes makes a good hand warmer warmer but but is not cost cost effective effective.. The temperatur temperaturee of the hand warmer increased by 26.7℃. However, at a cost of $0.68 per 10g of chemicals, a profit would not be made if the hand warmer is priced at around $1.00. If the retail price of the hand warmer increases, not as many people will buy it and the profits will still be lacking. Syllabus Questions
1. This lab demonst demonstrated rated that that various various chemicals chemicals can can have different different energy energy changes. changes. The desired purpose was achieved because the energy changes were noted when determining what would be considered an effective hand warmer. 2. The resu result ltss sshow how that that Na2CO3 is the most cost-effective solute when creating the hand warmer. However, LiCl had the largest temperature increase.
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3. Some pos possib sible le sour sources ces of of error error are: are: a. Incorr Incorrect ect temper temperatu ature re measure measuremen mentt b. Incorrect water mass measurement c. Incorr Incorrect ect solute solute mass mass meas measure uremen mentt 4. I learned that that there are are multiple multiple possibilitie possibilitiess of chemicals chemicals to create create an effective effective hand warmer. I also learned how to use u se the stirrer and create a calorimeter. Honors/AP Chemistry Lab Rubric
Part of the
Description
Lab
Points
Points
Earned
Possible
Pre-Lab Assignment
Answered all question in lab document as instructed; questions are answered correctly
60
60
Pre-Lab Checklist
Included in the lab notebook: name, lab title, title, date, name(s) of lab partner(s), purpose statement, materials list
10
10
Procedure
Procedure is listed concisely and clearly. Corrections are made to note any changes in the given procedure.
10
10
Data
All data is clearly listed or is in table format. Data is labeled with appropriate units.
10
10
Neatness
All information is legible, easy to read, and easy to follow
10
10
Data Analysis
Data analysis includes sample calculations when necessary. All work is shown, with answers clearly marked and in correct units.
50
50
Conclusion
All conclusion/post lab questions are answered in complete sentences.
50
50
200/200 = 100 Great Job!
