Course: Chemistry, Grade 12, University preparation (SCH 4U)
Strand/Unit: Energy Changes and Rates of Reaction
Overview: Physical changes that involve liquids and aqueous solutions can be studied using a polystyrene calorimeter like the one shown in Figure 1. Such materials can be applied to practical thermochemical systems. For example, when athletes are injured, they may immediately hold an “instant cold pack” against the injury; and over time, the athlete may apply “instant hot pack” to help recover. The medical hot/cold pack operates on the principle that certain salts dissolve endothermically in water, while others dissolve exothermically. The amount of heat per unit mass involved in the dissolving of a compound is a characteristic property of that substance. It is called the enthalpy of solution. The purpose of this experiment is to use calorimetry to determine the enthalpy of solution of an unknown salt, and then to use that value to identify the salt in a medical hot/cold pack, from a list of possible candidates (see table 1, which contains the theoretical values).
Figure 1. A simple laboratory calorimeter consists of an insulated container made of two nested polystyrene cups, a measured quantity of water, and a thermometer. The chemical system is placed in or dissolved in the water of the calorimeter. Energy transfers between the chemical system and the surrounding water are monitored by measuring changes in the temperature of the water.
- How can calorimetry be used to determine the identity of an unknown salt?
- What does the value of enthalpy change indicate about heat transfer?
- How could this knowledge of heat transfer extend our understanding of medical hot/cold packs?
- 3.5 class periods (assume 70 minutes per class).
- Time required depends on students’ background knowledge, skill set, and level of interest
- To relate science to technology, society and the environment.
- Develop the skills, strategies, and habits of mind required for scientific inquiry.
- A1. Demonstrate scientific investigation skills (related to both inquiry and research in the four areas of skills (initiating and planning, performing and recording, analysing and interpreting, and communicating).
- D2. Investigate and analyze energy changes and rates of reaction in physical and chemical processes, and solve related problems.
- A1.2 select appropriate instruments (e.g., glassware, calorimeter, thermometer) and materials (e.g., chemical compounds and solutions), and identify appropriate methods and techniques, and procedures for each inquiry.
- A1.4 apply knowledge and understanding of safe laboratory practices and procedures…interpret WHMIS symbols…handling and storing laboratory equipment…using appropriate personal protection.
- A1.5 conduct inquiries, controlling relevant variables, adapting or extending procedures as required, and using appropriate materials and equipment safely, accurately, and effectively, to collect observations and data.
- A1.6 compile accurate data from laboratory…and organize and record the data, using appropriate formats, including tables, flow charts, graphs, and/or diagrams.
- A1.11 communicate ideas, plans, procedure, results and conclusions…using appropriate language and a variety of formats.
- A1.12 use appropriate numeric, symbolic, and graphic modes of representation, and appropriate units of measurements (e.g., SI units, imperial units).
- D2.1. use appropriate terminology related to energy changes and rates of reaction, including, but not limited to: enthalpy, activation energy, endothermic, exothermic, potential energy, and specific head capacity [C].
- D2.3. solve problems involving analysis of heat transfer in a chemical reaction, using equation Q = mc∆T (in J/mol) [AI, C].
- D2.4. plan and conduct an inquiry to calculate, using a calorimeter, the heat of reaction of a substance, compare the actual heat of reaction to the theoretical value, and suggest sources of experimental error [IP, PR, AI, C].
- D3.3 explain how mass, heat capacity, and change in temperature of a substance determine the amount of heat gained or lost by the substance.
(Ontario Ministry of Education, 2008)
- Enthalpy changes; calorimetry; endothermic and exothermic processes.
Prior Skill Sets:
- How to set up the coffee-cup calorimeter apparatus.
- The proper use of the following instruments:
- Scoopula to obtain a certain mass of the salt.
- Using the analytical balance accurately (tare first, then add salt).
- Recording mass to two decimal places.
- Using the thermometer to measure changes in temperature to one decimal place.
- Effectively swirling the calorimeter to ensure effective mixing.
- Differentiate between system and surrounding.
- Relationship between heat and temperature.
- Calculating enthalpy changes given specific heat capacity, mass, change in temperature.
- Determining if a process is exothermic or endothermic from the ∆H value.
- How a calorimeter works.
- Determining ∆H using calorimetry by considering limiting reactants.
- Identify various laboratory instruments including, analytical balances, beakers, thermometers, et cetera.
Materials and Equipment:
Table 1. Enthalpies of solution for compounds in a Medical Hot/Cold Pack
Enthalpy of Solution (kJ/g)
Ammonium chloride, NH4Cl
Potassium nitrate, KNO3
Ammonium nitrate, NH4NO3
Sodium acetate trihydrate, NaC2H3O2·3H2O
Potassium chloride, KCl
Calcium chloride, CaCl2
Sodium acetate anhydrous, NaCH3COO
Potassium hydroxide, KOH
Sodium hydroxide, NaOH
- Students should adhere to the following laboratory practices which include, but not limited to:
- Avoid any horseplay with and practical jokes on other students using chemicals or laboratory equipment.
- Coats, bags, cell phones, and other personal items should not be allowed in the laboratory space.
- Wear proper safety equipment as instructed by the teacher (goggles, lab coat, closed-toe and closed heel shoes).
- Remove loose clothing and jewelry, and tie back long hair.
- No eating, drinking, or chewing gum in the laboratory.
- No ingesting or smelling of chemical substances.
- Never handle solids with the fingers. Instead, use a scoopula or its equivalent.
- Never return excess solids to its container, as it may result in cross-contamination.
- Know where the emergency exits are located and where to go if the classroom or building is evacuated.
(Science Teachers’ Association of Ontario, 2002)
- In the event of a broken mercury thermometer:
- Clear the area of the spill and provide maximum ventilation before cleaning up.
- Placing plastic bags over shoes may avoid extending the mercury contamination beyond its original area.
- Mercury cleanup kits are effective for small or modest spills. For larger spills, possibly consider a mercury vacuum cleaner. Mercury must be disposed of as a hazardous waste.
(Science Safety Handbook for California Public Schools, 2014)
- Following is the precautions of the various salts that will be used:
- NH4Cl, ammonium chloride, can cause skin and eye irritation. Keep away from acids, bases, and lead salts.
- NH4NO3, ammonium nitrate, is highly reactive and explosive if heated. Can explode at lower temperature if contaminated. Keep away from oxidizing agents, reducing agents, metals, and organic materials.
- CaCl2, calcium chloride, is an irritant, but low hazard.
- KCl, potassium chloride, low hazard.
- Potassium nitrate, KNO3, an oxidizing agent. Can form explosive mixtures with combustible material. Keep away from reducing agents and organic material.
- NaOH, sodium hydroxide, is highly corrosive. Keep away from acids, and metals.
- Dispose all salt solutions in the disposal beaker provided by the teacher.
- Sweep up with a brush into a dustpan, taking care to avoid raising dust. Wipe the area with a damp disposable cloth.
(Science Teachers’ Association of Ontario, 2002; High School Science Safety Resource Manual for Newfoundland and Labrador Schools, n.d.)
Instructional Planning and Delivery:
Prior to Day 1
(at the start of the semester)
(1) Note-taking strategies: *30 minutes*
(2) Common lab equipment handout:
Leading up to this day, in preparation for the inquiry-based activity, students were assigned one of their note-taking assignments to be due on this day.
(1) Note-taking assignment: *2 minutes for collection*
Students will be encouraged to preview the following topics from their textbook:
And, make notes using the abovementioned methods. Students will need to demonstrate the effective use of each method.
(1.1) Teacher Tip:
When assessing their notes, watch for the following alternative conceptions:
Once the note-taking assignment has been collected at the beginning of class, we begin our discussion around calorimetry.
(2) Building on prior knowledge: *15 minutes*
(2.1) Guiding Question: Where did these ∆H values come from? In other words, how did one determine the values presented in tables?
(2.2) Teacher Tip:
(3) Link to real world scenarios: *10 minutes*
(3.1) Guiding Question: In the real world, why is it necessary to determine the amount of energy absorbed or released?
(4) Introduce coffee-cup calorimetry: *5 minutes*
(4.1) Teacher tip:
(5) Recall Law of Conservation of Energy: *10 minutes*
(5.1) Teacher tips:
(6) Analyze a sample calorimetry problem: *15 minutes*
(6.1) Teacher tip:
(7) Video on Calorimetry: *5 minutes*
(8) Homework: *2 minutes to deliver the instructions*
(8.1) Curriculum outcomes:
(1) Peer-evaluation of homework problem set: *20 minutes*
(2) Taking up homework as a class: *10 minutes*
(2.1) Teacher tip:
(2.2) Source of Alternative Conception:
(3) Preparation for the inquiry activity next class: *25 minutes*
(4) Administer the Pre-lab quiz: *15 minutes*
(4.1) Curriculum Outcomes:
(1) Reinforcement of the inquiry activity: *15 minutes*
(1.1) Teacher tip:
(2) Teacher acts as a facilitator: *45 minutes*
(2.2) Teacher tip:
Monitor safe laboratory practices:
Ensure equal distribution of labour:
(2.3) Curriculum Outcomes:
(3) Clean up: *10 minutes*
(1) Demonstration of student learning: *2 minutes for collection*
(2) Administer the Post-lab quiz: *15 minutes*
(2.1) Curriculum Outcomes:
(3) Continue on to the next topic
(SEE SECTION BELOW)
- Technology: Medical “talking” thermometers that read out results can be an effective alternative for students with a visual impairment or dyslexia.
- Print: Large print books (or documents) should be incorporated to accommodate students with a visual impairment. In addition, trade books would appeal to ESL students, and to those who are linguistically and mathematically challenged, since these books are written for a scientific audience without the scientific vocabulary found in textbooks.
- Community: It is strongly recommended that teachers collaborate with special education or resource teachers in the school, who have experience working with students that have an individualized education plan (IEP).
Student Support Resources:
Related Background Resources/Links:
Avsec, S., Kocijancic, S. (2016). A Path Model of Effective Technology-Intensive Inquiry-Based Learning. Educational Technology & Society, 19 (1), 308-320.
Bloom B, Krathwohl D, Masia B, eds. (1971). Taxonomy of Educational Objectives: The Classification of Educational Goals-Handbook II-Affective Domain. New York, NY: David McKay Company, Inc.
California Department of Education. (2014). Science safety handbook for California public schools. Retrieved from: https://www.cde.ca.gov/pd/ca/sc/documents/scisafebook2014.pdf
Harlen, Wynne. (2013). Inquiry-based learning in science and mathematics. Review of Science, Mathematics and ICT Education, 7 (2), 9-33.
High School Science Safety Resource Manual for Newfoundland and Labrador Schools. Retrieved from: https://www.ed.gov.nl.ca/edu/k12/curriculum/documents/science/LabSafetyGuidelines.PDF
Martinez, Isidoro. (1995). Heat of Solution Data for Aqueous Solutions. Retrieved from: http://webserver.dmt.upm.es/~isidoro/dat1/Heat%20of%20solution%20data.pdf
Mccord, P. (2011). Calorimetry. Retrieved from: https://www.youtube.com/watch?v=EAgbknIDKNo
Mustoe, F., Jansen, M., Webb, M., Doram, T., Hayhoe, C., Gaylor, J., Ghazariansteja, A. (2004). Chemistry. McGraw-Hill Ryerson, 661-667.
Ontario Ministry of Education. (2008). The Ontario curriculum grades 11 and 12: Science. Retrieved from: http://www.edu.gov.on.ca/eng/curriculum/secondary/2009science11_12.pdf.
Science Teachers’ Association of Ontario. (2002). Stay Safe: A health and safety reference for secondary school science. Ontario: Author.
Scientific Laboratory Materials. (2016). Retrieved from: https://www.wiatrade.com/scientific-laboratory-materials
Weigel, F., Bonica, M. (2014). An Active Approach to Bloom’s Taxonomy: 2 Games, 2 Classrooms, and 2 Methods. The United States Army Medical Department Journal. Retreived from: http://www.cs.amedd.army.mil/amedd_journal.aspx
- Investigate how much energy can either be absorbed or released by the medical hot/cold pack for it to be effective to student-athletes. Work backwards to determine the type of salt, and the quantity of both salt and water required. Students should state a hypothesis regarding the effectiveness of hot/cold packs by manipulating the mass of salt used, while keeping the mass of water constant. Students should also determine the materials that will be required to build a medical pack. Using a guided inquiry approach, students could be encouraged to conduct a series of tests on student-athletes at their schools, determining the best treatment for athletes. Their results could be presented at their school science fair or at a business exposition.
- From coffee-cup to bomb calorimetry will engage students in determining how much energy (calories) present in various foods. Another example of guided inquiry, where students will have to design a bomb calorimeter, which will necessitate greater attention to safety. Students can, for example, compare the calorie contents of peanuts with candy. This will also require the construction of a hypothesis, planning and execution of an experimental design, which will be followed by analysis and conclusions. Student findings could be displayed at the school’s science fair, in an attempt to raise awareness of diet and healthy active living.
- Instant food warmer heat pack can be used to prepare myriad of food from coffee to instant noodles. Students could develop their own heat packs that will warm food, without fire and electricity. Portability would be a huge selling point. Using a guided inquiry approach, food warmer heat pack’s effectiveness could be tested on various foods and the results could then be showcased at the school’s science fair or at a business exposition. See link: https://www.alibaba.com/product-detail/Top-Factory-Disposable-Pocket-Instant Food_60733706891.html?spm=a2700.7724857.normalList.13.124f39d5XpiAPN