Chemistry Lab #9 - This is a completed lab report for unit #9 that we received an A on. PDF

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This is a completed lab report for unit #9 that we received an A on....

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Using Calorimetry to Determine Specific Heat and Heat of Solution

Date of Submission: 11/15/2017 Lab Section: CHE110L-26 Purpose: The purpose of this lab was to use calorimetry to determine the specific heat of an unknown

metal and to measure the heat of solution of an ammonium salt. Procedure: The procedure is found on pages 71-79 in “General Chemistry CHE110L Laboratory Manual Fall 2017.” Data Tables: Carbon copies of data tables have been attached to the back of this lab report. Summary of Results: Specific Heat of Metal Unknown #

3

Specific Heat of Metal

0.746 J/g℃ Heat of Solution

Identity of Salt: KNO3 Experimental ΔHsolution (KJ/mol):

Trial 1: 28.5 KJ/mol

Trial 2: 28.5 KJ/mol

Average Experimental ΔHsolution (KJ/mol): 28.5 KJ/mol Theoretical ΔHsolution (KJ/mol): 36.2 KJ/mol Conclusion: The purpose of this lab, to use calorimetry to determine the specific heat of an unknown metal and to measure the heat of solution of an ammonium salt, was fulfilled. The specific heat of the unknown metal #3 was .764 J/g ℃ and the average experimental heat of solution was 28.5 KJ/mol. The specific heat of unknown metal 3 was 0.746 J/g ℃ and the average experimental heat of solution was 28.5 KJ/mol. The specific heat of unknown metal 3 was found by finding the mass of the water in the calorimeter (19.185 g) and the mass of the unknown metal (4.928 g). Next, the unknown metal was heated to 99.8 ℃ and the initial temperature of the water in the calorimeter was recorded to be 22.1 ℃. The heated metal was then added to the calorimeter and stirred and the final temperature of the calorimeter was recorded to be 25.5 ℃. Using this data, the heat of reaction of the water was calculated to be 273 J using the equation Q = m(g) x ΔT( ℃) x SH (J/g ℃). Because the heat of reaction of the water is equivalent to the negative heat of reaction of the metal, -273 J was set equal to m(g) x ΔT( ℃) x SH (J/g ℃) and the data collected was plugged into it. This was solved for the specific heat of the metal which was 0.746 J/g ℃. To find the average heat of solution of the salt, the water in the calorimeter was massed (19.072 g) and the salt was massed (2.001 g). Once the initial temperature was taken, the salt was added to the calorimeter and stirred until it was dissolved and the final temperature was recorded. The mass of the solution (21.073 g), change in temperature (6.4 ℃), and specific heat of water (4.184 J/g ℃) were plugged into the equation Q = m(g) x ΔT( ℃) x SH (J/g ℃) and the heat of solution for trial 1 was found to be 28.5 KJ/mol. This value was then averaged with our second trial (28.5 KJ/mol) and the

average heat of solution was found to be 28.5 KJ/mol. Sources of error for this lab include the potential for the metal to cool off when being transported from the boiling water to the calorimeter. Although it was transferred as quickly as possible, the metal could have decreased in temperature when it was removed from the beaker of boiling water. This would result in a false initial temperature reading for the metal that would be higher than it was in actuality. Consequently, the heat of reaction would be lower than in actuality. A second source of error for this lab was when the metal was added to the calorimeter, some of the water splashed out of the calorimeter. Because the calorimeter lost water, it reduced the mass of the water in the system even though the heat of reaction was calculated using the mass of the water before the metal was added. Therefore the calculated heat of reaction may have been higher than the actual heat of reaction because in actuality the water had less mass. Post-Lab Questions 1. 11.583 g of a metal are heated to 99.8 ℃. This poured in a calorimeter containing 25.118 g H2O at 24.7 ℃. The final temperature of the water and metal is 28/5 ℃. What is the specific heat of the metal? Q = m(g) x ΔT(℃) x SH (J/g℃) QH2O = -Qmetal QH2O = (25.118 g) (28.5℃ - 24.7 ℃) (4.184 J/g℃) = 399.36 J Qmetal = -399.36 J -399.36 J = (11.583 g) (28.5℃ - 99.8℃) SHmetal SHmetal = (-399.36) / (11.583 g) (28.5 ℃ - 99.8℃) = .484 J/g℃...