Calorimetry And Specific Heat Lab Report

Calorimetry and Specific Heat
Tessa Williams
Chemistry 111
11/13/13

Abstract:
In this experiment, the specific heat and the density of an unknown metal was determined in order to identify the unknown metal. The average specific heat of the unknown metal was 0.197˚C and was determined using a calorimeter. The density of the unknown metal was 6.57 g/mL and was determined using a cylinder and displacement. Using the specific heat value of the unknown metal and its density, it was determined that the unknown metal was Tin.
Introduction:
The first law of thermodynamics states that energy must be conserved in any thermodynamic process. The change in internal energy of a system is equal to the head added
to the system minus the work done by the system. The enthalpy change is the heat that is transferred under constant pressure. The change in enthalpy only depends on the initial state and the final state and not by the path in which it happens because enthalpy is a state function. Any heat that flows from a system must be absorbed by the surroundings, and any heat that flows into a system must come from the surroundings. In order to measure the heat transferred in a reaction a calorimeter is used. The calorimeter is filled with a specific amount of water and the temperature of the water is measured. If a hot object, such as metal, is put into the water, the water’s temperature will increase controlled by the following equation:
(Equation 1) ∆Hw = qw = mwcw∆Tw

Where mw is the mass of the water, cw is the specific heat of water or 4.179J/g˚ C, and ∆Tw is the temperature change of the water or Tfinal - Tinitial.
Because the calorimeter is insulated, the metal object causes the water to lose the heat it has gained.

(Equation 2) qw = -qm

(Equation 3) mwcw∆Tw = - mmcm∆Tm

(which can be converted to)

(Equation 4) Cm =

Equation 4 can then be used to calculate the specific heat of the metal object. By finding the density of the unknown metal and using the above equation to find the specific heat of the unknown metal, the metal can then be identified.

Experimental Procedures:
In the beaker on the hot plate pour 250mL of water into it and bring it to a weak boil.
While waiting on the water to boil, retrieve a piece of unknown metal to be identified and record its ID letter and its mass. Once the mass of the unknown metal is recorded, put the metal into the boiling water. While waiting on the water and the metal to achieve the same thermal equilibrium, get a coffee cup and measure its mass. Then pour about 50mL of water into a coffee cup, measure the mass of the water and the coffee cup and then determine the mass of the water alone (mass of water and coffee cup – mass of coffee cup). Record the temperature of the boiling water on the hot plate with the metal and then record the temperature of the water in the coffee cup before adding the metal. Use the string attached to the metal to transfer the metal from the hot water bath to the calorimeter. Using a piece of cardboard to cover the top of the calorimeter, record the temperature of the water in the calorimeter. Repeat the experimental procedure three more
times.

Results and discussion:
For each trial the mass of the metal (Mm), mass of the cup, mass of the water (Mw), temperature of the calorimeter with the water and the metal (Tf) minus temperature of the boiling water (MI), and temperature of the colorimeter with the water and the metal (Tf) minus the temperature of the water in the calorimeter (WI), and was recorded.

Trial 1:
Mm: 57.99 g
Mw: 108.41 g
MI (temperature): 96.7˚C
(Tf - MI = ∆Tm)(-75.8˚ C change = ∆Tm)
WI (temperature): 19.0˚C
(Tf - WI = ∆Tw) (1.9˚ C change = ∆Tw)
Tf: 20.9˚ C

Trial 2:
Mm: 58.00 g
Mw: 105.34 g
MI (temperature): 93.3˚C
(Tf - MI = ∆Tm) (-71.1˚ C change = ∆Tm)
WI (temperature): 20.3˚C
(Tf - WI = ∆Tw) (1.9˚ C change = ∆Tw)
Tf: 22.2˚ C

Trial 3:
Mm: 58.00 g
Mw: 1.74 g
MI (temperature): 90.5˚C
(Tf - MI = ∆Tm) (-68.7˚C change = ∆Tm)
WI (temperature): 19.8˚C
(Tf - WI = ∆Tw) (2˚C change = ∆Tw)
Tf: 21.8˚C

Use equation 4 to calculate the specific heat of the unknown metal object (cm).

(Equation 4) Cm =

Trial 1: Cm =

Cm = 0.196 ˚C

Trial 2: Cm =

Cm = 0.203 ˚C

Trial 3: Cm =

Cm = 0.193 ˚C

Report the final answer as the average of all three trials, which is 0.197˚C.
Next use the standard deviation formula to determine how much variation from the average exists.

Standard deviation: 5.15 x
The density of the unknown metal was also found using a graduated cylinder by displacement. The density of the unknown metal was 6.57 g/mL. By using the unknown metals specific heat and density, it was determined that the unknown metal was Tin.
Conclusion:
The average of all three specific heats was 0.197˚C and the density of the unknown metal was determined to be 6.57g/mL.
Using this specific heat value of the unknown metal and the density of the unknown metal, it was determined that the unknown metal was Tin. According to the standard deviation equation, 5.15 x was the amount of variation that existed. Determining specific heat using a calorimeter is not always perfect. There may be some human or instrumental errors that cause the data to show inconsistencies. For example, the unknown metal may not have set in the water bath long enough to reach the same temperature as the water causing inaccurate results when reading temperature. Also, a result could have been record incorrectly causing the specific heat to be wrong. These experiments lead to reliable results, which in turn determined that the unknown metal was
Tin.
Literature Cited:
1. Henderson, T. (1996). Calorimeters and calorimetry. http://www.physicsclassroom.com/about.cfm
2. Columbia University. (2013). Calorimetry. Columbia Electronic Encyclopedia, 6th Edition, doi: MasterFILE Premier