The initial temperature of the object is taken to be

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Unformatted text preview: y both the beaker (remember it had HCl in it) and the coffee cup calorimeter. Get 20.00 mL of HCl in the beaker and 20.00 mL of NaOH in the coffee cup calorimeter. Once again, determine the temperature of both solutions, being careful to rinse off the temperature probe and to dry it between solutions. Begin taking temperature measurements of the NaOH, and quickly, but carefully (to avoid splashing) pour the HCl into the NaOH. Cover the calorimeter and swirl carefully. Continue taking temperature readings until the temperature levels off, or until it drops slightly. All solutions can go down the drain with running water; clean your equipment. Return the calorimeter. Calculations: For any heat transfer which does not involve phase changes, we have q=mc∆T, where ∆T=Tfinal-Tinitial. Here, q is heat (measured today in “calories”), m is mass (measured in grams), T is temperature (measured in degrees Celsius), and c is the specific heat. For water, we have cwater =1cal/go C. Since qobject = - qcalorimeter, we have mobject cobject ∆Tobject = mwatercwater∆Twater . Thus, cobject = -mwatercwater∆Twater/mobject ∆Tobject . The mass of the object was measured directly. To determine the mass of the water, subtract the mass of the calorimeter from the mass of the water and calorimeter. Plot a graph of temperature versus time (by convention, we always mean plot “y versus x”, so to say “plot temperature versus time” implies that temperature belongs on the y axis, while time belongs on the x axis). From the graph, determine ∆Twater, and the final temperature. Since heat is being absorbed by the water, ∆Twater should be a positive number. The initial temperature of the object is taken to be 100o C (since, after all, it started in boiling water. The final temperature of the object should be the same as the final temperature of the calorimeter if you were patient enough. Thus, ∆ Tobject =Tfinal-100, and should be a negative number. Calculate the specific heat of each object and report them. From a table of specific heat values, can you predict what the objects were made of? Heat of Reactions: You will need to calculate the heat of dilution for both the HCl and the NaOH. For NaOH, determine the initial temperature by the initial temperature of the NaOH and the water; if they are different, use the average as your initial temperature. The final Dakota State University page 180 of 232 Experiment 17: Calorimetry General Chemistry I and II Lab Manual temperature is the maximum temperature reached on mixing. The heat of mixing, then, is simply ∆HNaOH,mix =m∆ T where ∆ T is the change in temperature and m is the mass of the total solution (take it to be 40 grams; we are assuming the density is 1.00 g/mol). In an analogous fashion, determine ∆HHCl,mix . The total energy change, ∆ Htotal is determined the same way as above, but use the run where you mixed the HCl and NaOH. To find the heat of reaction, note that ∆Htotal=∆Hrxn +∆HNaOH,mix +∆HHCl,mix Use the values you’ve calculated to find ∆Hrxn; this is the heat of reaction. Divide this value by the number of moles of acid (or base, whichever is less) as calculated by the concentration of the acid or base and the volumes we’ve...
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