Introduction LAB 9: Calorimetry: Part 2 [30 points] Most physical processes and chemical reactions cither release or abs

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Introduction LAB 9: Calorimetry: Part 2 [30 points] Most physical processes and chemical reactions cither release or absorb energy, usually as heat. Therefore, to better understand chemistry, chemists have quantitatively measured the amount of heat absorbed or released by many different processes and reactions. One technique used to do this is known as calorimetry. To understand how one uses calorimetry, one must first understand that the flow of heat has to be defined in terms of moving from "one someplace" to "another someplace". The two "some places" are the system and the surroundings. The system is an arbitrary mental separation of one part of the universe from the rest of the universe. In other words, it is what one is studying. The surroundings is the rest of the universe. The flow of heat is defined as "from surroundings to system", and energy changes that do flow in that direction has values that are > 0. Energy changes that flow from system to surroundings have values that are <0. Processes and reactions that cause the flow of heat to go from surroundings to system are described as endothermic (endo-= "in"; thermic - heat). Processes and reactions that cause the flow of heat to go from system to surroundings (and thus <0 and are far more common) are described as exothermic (exo-="out"). Obviously, it is not possible to measure how much heat flows into the surroundings if the surroundings is essentially the entire universe. Therefore, the technique of calorimetry uses thermally insulating materials such as Styrofoam so that a small part of the universe can be isolated from the rest. By experimental design, (at least, idcally) no heat enters or leaves the calorimeter. Paraphrasing a famous slogan about Las Vegas, "What happens in the calorimeter stays in the calorimeter." This allows use to divide the events that occur in a calorimeter into individual processes knowing that the sum of the amounts of heat transferred by all of the processes combined has to equal 0 exactly. As an example, consider what happens when ice at 0°C is added to water in a calorimeter. The ice melts, the water cools, the calorimeter cup cools, and the water from the ice warms from 0°C to the final temperature. Thus, this experiment would have 4 processes and therefore 4 amounts of heat that add to 0. The letter "q" is used to symbolize an amount of heat. Thus, q1+q2+q+q4= 0, and one would use this equation to evaluate the value of what one was measuring. The processes that occur inside of a calorimeter can be divided into two types-processes that involve a material changing temperature, and processes for which one can write an equation, such as chemical reactions and changes of state. For processes where a material changes temperature, one uses either the equations q=m-SH-AT or q=Cp-AT where m is the mass of the material, SH is the specific heat of the material, Cp is the heat capacity of the material, and AT is the change in temperature of the material. One uses the first equation when the mass of the substance is variable, such as the amount of water added to the calorimeter. One uses the second equation when the mass isn't variable, such as the amount of heat transferred to the Styrofoam cup. For processes for which one can write an equation, one uses the equation, q=AH-(nused/nequation)
use. where nused is the number of moles of the limiting reactant actually used in the experiment, nequation is the coefficient for the limiting reactant, and AH is the change in enthalpy for the process. As the class has not yet studied either chemical equations, limiting reactants or AH yet, file this equation for possible later In the quantitative part of today's lab, you will compare the specific heat of hot water to that of room-temperature water, and you will measure the specific heat of a metal. Since the heat transferred to the Styrofoam is a small amount, it will be ignored in today's lab. Thus, in general terms, there are two processes for the two quantitative experiments-the hot material cooling, and the room-temperature water warming. If one represents the heat of the hot material cooling as quand the heat of the water warming as qw, then Thus, Thus, by substitution Thus, q+qw0 qh=-qv mSHAT₁-mwSH.AT SH=-mwSH.ATW/(mbATH) This is the equation you will be using to determine the specific heats.
Modifications to Procedure: Materials needed: Styrofoam cups A small square piece of cardboard with a small hole; the piece should be large enough to entirely cover the mouth of a Styrofoam cup, and the hole should be just large enough for the thermometer. Paper clips Either un-iodized salt or "No Salt" sodium free salt substitute, which is mostly KCI Washing soda (sodium carbonate); NOT baking soda, which is sodium bicarbonate Distilled water, which is used in place of de-ionized water Small sandwich bags (you will need 3 for the experiment) Procedure modifications: . 3 Parts A and B: Essentially unmodified except that you will be using either salt or No Salt for part A and washing soda (Na2COs) for part B, and that you have to put the salt into the sandwich bag yourself. I suggest 3 teaspoons of the salt and 25 ml. of water. (In part A, the No Salt will have the more noticeable effect.) Part C: Steps 1-6, 10, 13, and 14 are unmodified and done as written Step 7: Pour the 50-mL of water into a third Styrofoam cup Step 8: Put the cup into a microwave oven Step 9: Microwave for 2 minutes Step 11: Swirl the hot water Step 12: Measure the temperature of the hot water Part D: Step 1: as written Step 2: weigh 10 small paper clips and place in a sandwich bag Step 3: add about 25 mL of tap water to a Styrofoam cup Step 4: microwave for 2 minutes Step 5: remove the cup from the microwave and place the sandwich bag into the cup such that the paper clips are below the level of the water; allow the paper clips to sit in the water for 10 minutes. Step 6: at the end of the 10 minutes, measure the temperature of the hot water and then quickly pour the paper clips into the room temperature water; after that proceed with the step as written. Step 7: as written PLEASE SEE THE PROCEDURE ON NEXT PAGE
Procedure Part A: Enthalpy of Solvation of ammonium nitrate 1) Obtain a plastic bag containing NH4NO3. 2) Observe the exterior temperature of the bag by gently rubbing your hands on the bag and have your lab partner(s) do the same. 3) Half-fill a 150-milliliter beaker with DI-water. 4) Quickly pour the water into the bag and observe the temperature as you again rub the bag; have your lab partner(s) do likewise. 5) When finished, discard the contents of the bag down the sink and put the bag into the trash. Part B: Enthalpy of Solvation of calcium chloride 1) Obtain a plastic bag containing CaCl₂ and repeat the procedure from part A. Part C: Specific Heat of Hot Water 1) Obtain a large beaker containing two Styrofoam cups, a cardboard lid, and a thermometer. 2) Weigh the two Styrofoam cups. 3) Use a graduated cylinder to measure about 40 ml. of DI-water to the nearest tenth of a m... 4) Pour the water into the cups. 5) Weigh the cups and water. 6) Use a graduated cylinder to measure about 50 mL of DI-water to the nearest tenth of a ml.. 7) Pour the water into a 150-milliliter beaker. 8) Put the beaker onto a hot plate and place a watch glass on the beaker. 9) Turn on the hot plate and heat the water until it is boiling. 10) As the water heats, put the cardboard lid on the cups, put the thermometer through the hole in the cardboard lid, and measure the temperature of the water in the cups to the nearest tenth of a °C. The thermometer bulb should be completely immersed in the water, but it shouldn't be touching the cups. Read steps 11)-13) so that you can do them quickly without looking at the instructions. 11) When the water on the hot plate boils, turn off the hot plate, lift the beaker and watch glass off of the hot plate, and carefully swirl the hot water. 12) Carefully place the watch glass on the counter and, while holding the beaker, measure the temperature of the hot water to the nearest tenth of a °C. The thermometer bulb should be fully immersed, but it shouldn't be touching the glass. 13) Quickly pour the hot water into the calorimeter, replace the cardboard lid and thermometer, and measure the temperature of the water every 15 seconds for the next 2 minutes. Carefully swirl the mixture between temperature measurements, but do not use the thermometer as a stirring rod. You should see the temperature plateau. The final temperature is the highest temperature in the plateau. 14) When you are done measuring the temperature, weight cups and water, then pour the water down the sink. Do not dry the cups, as the residual water will simply become part of the next experiment.
Part D: The Specific Heat of a Metal 1) Repeat steps 3)-5) of part C. 2) Obtain a piece of metal, weigh it, and place it in an appropriately sized beaker. If possible, the metal should lie flat. 3) Add tap water to the beaker until the level of the water is about 5 mm above the metal. 4) Repeat steps 8)-10) of part C. Be prepared to do steps 5)-6) of part D quickly. 5) When the water boils, repeat steps 11) and 12) from part C. 6) Use tongs to quickly transfer the metal to the calorimeter. Replace the lid and thermometer and measure the temperature of the water every 15 seconds for the next two minutes. Swirl the calorimeter between temperature readings. As before, the final temperature is the highest temperature of the plateau. 7) Clean up your lab station. Lab Report Part A: Enthalpy of Solution of NHANO [2 points] 1. Qualitative assessment of temperature before adding water: 2. Qualitative assessment of temperature after adding water: 3. Direction of the flow of heat: from 4. Description of reaction: Part B: Enthalpy of Solution of CaCl₂ [2 points] 1. Qualitative assessment of temperature before adding water: 2. Qualitative assessment of temperature after adding water: 3. Direction of the flow of heat: from 4. Description of reaction: Part C: Specific Heat of Hot Water-Data- 1. Mass of Styrofoam cups: 2. Volume of room temperature water: 3. Mass of Styrofoam cups and cold water: 4. Volume of hot water: 5 to -thermic to -thermic 8 ml. g ml [0.5] [0.5] [0.5] [0.5]
5. Initial temperature of room temperature water: 6. Initial temperature of hot water: 7. Temperature of water in calorimeter after mixing 0 seconds: 15 seconds: 30 seconds: 45 seconds: 60 seconds: 75 seconds: 90 seconds: 105 seconds: 120 seconds: "C "C "C "C "C °C °C "C "C 8. Temperature final (highest T) of water in calorimeter: 9. Mass of Styrofoam cups and cold water and warm water: Part D: Specific Heat of Metal-Data 1. Mass of Styrofoam cups: 2. Volume of room temperature water: 3. Mass of Styrofoam cups and cold water: 4. Mass of metal: 5. Initial temperature of room temperature water: 6. Initial temperature of hot metal: 7. Temperature of water in calorimeter after adding metal 0 seconds: °C 15 seconds: 30 seconds: 45 seconds: 60 seconds: 75 seconds: 90 seconds: 105 seconds: 120 seconds: °C 8. Temperature final (highest T) of water in calorimeter: 6 °C °C °C °C °C °C °℃ "C "C "C 8 8 ml. 8 8 °C °C [0.5] [0.5] [2] [1] [1] [0.5] [0.5] [0.5] [0.5] [0.5] [0.5] [2] [1]
Part C: Specific Heat of Hot Water-Calculations (4 points] 1. Mass of room temperature water Mass of Styrofoam cups and room temperature water. -Mass of Styrofoam cups: Mass of room temperature water (m): 2. Specific heat of room temperature water Specific heat of room temperature water (SHw): 3. Change in temperature of room temperature water Final temperature: -Initial temperature of room temperature water Change in temperature of room temperature water (ATw) 4. Mass of hot water Mass of Styrofoam cups and room temperature water and hot water: -Mass of Styrofoam cups and room temperature water: Mass of hot water (m): 5. Change in temperature of hot water Final temperature: - Initial temperature of hot water: Change in temperature of hot water (ATH) 6. Specific heat of hot water mw SHw ATw -( my ATh g)(4.184 J/g °C) g) ( °C) 11/1 4.184 J/g-"C °C °C °C 11/1 °C °C J/g-°C
Part D: Specific Heat of Metal-Calculations [4 points) 1. Mass of room temperature water Mass of Styrofoam cups and room temperature water. -Mass of Styrofoam cups: -Mass of room temperature water (m): 2. Specific heat of room temperature water Specific heat of room temperature water (SH.): 3. Change in temperature of room temperature water Final temperature: -Initial temperature of room temperature water - Change in temperature of room temperature water (AT) 4. Mass of metal Mass of metal (mm): 5. Change in temperature of metal Final temperature: - Initial temperature of metal: - Change in temperature of metal (ATm) 6. Specific heat of metal -mwSHWATw mm ATm gX4.184 J/g-*CX g) °C) °C) g 4.184 J/g °C °C °C °C °C °℃ °C J/g.°C
Questions 1) If one assumes that the specific heat capacity of water doesn't change with temperature, what result would you expect for part C? Calculate your % error based on this value and comment on possible sources of error. [0.5) 2) At 100°C, the specific heat capacity of water is actually 4.2157 3/g-"C. Calculate your % crror based on this valuc. [0.5] 3) Assume that the density of water is 0.998 g/ml. Calculate the amount of water lost to evaporation when you heated the water in part C. [1] 4) Would having some of the water splash out when the metal was dropped into the calorimeter erroneously increase or erroneously decrease the reported specific heat? Explain. [1]
5) There are 4,184 joules in a food Calorie (note the capital "C"). A 70.-gram serving of Kraft Macaroni and Cheese contains 16 grams of carbohydrate (4.0 Cal/g), 3.0 grams of fat (9.0 Cal/g), and 9.0 grams of protein (4.0 Cal/g). Calculate the temperature increase of 2.0 kg of water if all of the food [1] energy in 150.0 grams of Kraft Macaroni and Cheese goes entirely into heating the water. 6) When 49.834 grams of a metal at 100.0°C is added to 46.497 grams of water at 23.2°C, the temperature of the water increases to 25.6°C. If the metal comes from the list below, what is the identity of the metal? [1] Metal specific heat 0.436 cal/g °C 0.092 cal/g °C 0.030 cal/g °C 0.056 cal/g °C Be brass Au Ag Mg Fe 0.243 cal/g °C 0.108 cal/g °C