Essay on Lab 4 formal report

Submitted By jvleeson
Words: 1944
Pages: 8

Introduction/Purpose
In all reactions, elements or compounds undergo changes in internal energy. One component that has a major effect on the changes in internal energy is the transfer of heat. Calorimetry is the study of the changes in heat that accompany all chemical reactions. Calorimetric experiments are always done under controlled, specific conditions. In this case, the experiments will be done using an expanded polystyrene calorimeter to measure the heat of dissolution of NaOH as well as its concentration (using the heat of a neutralization reaction between NaOH and HCl). However, this can only be done accurately if the heat capacity of the calorimeter is determined, that is, the amount of energy needed to raise its temperature by 1°C (or K). In order to do this, a known mass of cold water will be added to a known mass of hot water in the calorimeter. As heat is lost by the calorimeter and by the hot water while begin absorbed by the cold water, the following equation can be used to determine the calorimeter’s heat capacity: . The calorimeter used is not a sealed system. Consequently, the reactions occur at constant pressure, and the heat of reactions are equal to the enthalpy change of the reaction, ΔH. To calculate the heat of dissociation per mole of NaOH (assuming heat is lost to the calorimeter), the following equation will be used:
. However, if it is assumed that no heat is lost to the calorimeter, qcal can be ignored in the equation. This equation is valid because it is assumed that no heat in the system is lost to the surroundings, and thus, qrxn + qcal + qsoln = 0. A similar equation can be used to determine the concentration of NaOH in a solution. Since it is known that ΔH = -55.90kJ/molH2O for all neutralization reactions involving strong electrolytes (because the heat of reaction essentially results from the formation of water from hydrogen ions and hydroxide ions), the concentration of NaOH in the solution can be calculated as follows: [. To calculate ΔHrxn, qcal may or may not be accounted for. The effectiveness of these methods can be determined by comparing them to the results obtained by using the mass of NaOH used and the volume of the solution.
Experimental Procedure
“The experimental procedure used for this experiment was outlined in the CHEM 120L manual, Experiment #4. All steps were followed without deviation.”
Experimental Observations
Part A
T(i) water = 23.0°C
Temperature of solution (every 10sec for 1min) (°C)
Temperature of solution (every min for 24min) (°C)

Mass (NaOH) used = 10.23g
(1) 24.0
(1) 33.0
(7) 35.5
(13) 34.25
(19) 33.0
Mass cal. = 48.25g
(2) 25.0
(2) 34.0
(8) 35.5
(14) 34.0
(20) 33.0

(3) 26.0
(3) 35.0
(9) 35.5
(15) 34.0
(21) 32.75

(4) 27.0
(4) 35.0
(10) 35.25
(16) 33.75
(22) 32.5

(5) 30.0
(5) 35.5
(11) 35.0
(17) 33.5
(23) 32.25

(6) 31.0
(6) 35.5
(12) 34.5
(18) 33.0
(24) 32.25

Part B
Mass of calorimeter with 125mL of heated DI water = 146.85g
Mass of calorimeter with 125mL DI water (after reaction is complete) = 269.65g
Initial temperature of cool water = 24.0°C
Temperature of mixture IMMIDIATLY after mixing = 33.2°C

Temp. of heated water at 5 1min intervals prior to mixing (°C)
Temp. of heated mixture at 1min intervals for 10min (°C)

(1) 44.75
(1) 33.0
(6) 32.0
(2) 43.5
(2) 32.0
(7) 32.0
(3) 43.0
(3) 32.0
(8) 32.0
(4) 43.0
(4) 32.0
(9) 32.0
(5) 42.0
(5) 32.0
(10) 32.0

Part C
Concentration of HCl from carboy = 1.167M
Temp. of HCl before mixing = 25.0°C
Temp. of NaOH before mixing = 25.0°C

Temperature after mixing at 5 second intervals for 1 minute (°C)

Temperature after mixing at 30 second intervals for 9 additional minutes (°C)

(1) 29.0
(7) 28.90
(1) 28.90
(7) 28.75
(13) 28.6
(2) 29.0
(8) 28.90
(2) 28.90
(8) 28.75
(14) 28.6
(3) 29.0
(9) 28.90
(3) 28.90
(9) 28.75
(15) 28.6
(4) 29.0
(10) 28.90
(4) 28.90
(10) 28.75
(16) 28.6
(5) 29.0
(11) 28.90
(5) 28.75
(11) 28.75
(17) 28.5
(6) 29.0
(12) 28.90
(6) 28.75
(12) 28.6
(18) 28.5

Results & Calculations
Part A –…