Thermometric Titration

Date: October 29, 2014
Title: Thermometric Titration
Purpose: To determine the concentration of sulphuric acid by thermometric titration
Background Information: A thermometric titration is a titration technique where the endpoints of the reaction are located from the enthalpy change between the reagents. In thermometric titration we make use of the fact that reactions in solution are accompanied by temperature changes and thus it is possible to follow the course of the reaction with a thermometer. A reagent of known concentration is added to the reagent of unknown concentration and the enthalpy changes presented on a graph to show the endpoint and maximum and minimum temperatures at which the reaction occurs. This will then be used to determine the concentration of the acid.
Materials/Apparatus: FB1, sulphuric acid (H2SO4(aq)), FB2, sodium hydroxide (NaOH(aq)), Styrofoam cups, thermometer, 50 cm3 measuring cylinders, stopper, foil paper, 250cm3 beaker
Procedure: The temperature of each solution was recorded, while taking care to wash and dry the thermometer before the temperature of the second solution was recorded. The temperature was read to the nearest 0.5°C and the temperature of each solution was recorded. The average temperature of the two solutions was then calculated. The styrofoam cup was supported in a 250cm3 beaker. One of the cylinders was used to transfer 40cm3 of FB2 NaOH(aq), into the styrofoam cup. The stopper or cover of FB2 was replaced to prevent any reaction of carbon dioxide in the air with NaOH(aq). The second measuring cylinder was used to transfer 10cm3 of FB1 H2SO4(aq) into the NaOH(aq) in the plastic cup. The mixture was stirred with the thermometer and the highest temperature obtained was noted. This temperature was recorded in Table 1.2 for experiment 1. The styrofoam cup was emptied, rinsed and dried and the experiment repeated with other mixtures shown in Table 1.2 and the highest temperature reached in the mixture was recorded.
Safety Considerations: Ensure that containers housing NaOH(aq) are covered or stoppered securely to prevent the NaOH(aq) from absorbing any carbon dioxide from the atmosphere.
Data Tables:
Table1.2; MAXIMUM TEMPERATURE RECORDED FOR REACTION FOR VOLUMES OF FB1 AND FB2
Experiment
1
2
3
4
5
6
Volume of FB2/cm3
40
35
30
25
20
15
Volume of FB1/cm3
10
15
20
25
30
35
Maximum Temperature/◦C
34.5
38.0
41.5
44.0
40.0
37.0

Average Initial Temperature= (FB1+FB2)/2 = (27.5◦C+29.0◦C)/2 =28.3◦C
TEMPERATURES AT VARYING NUMBER OF MOLES
Experiment
1
2
3
4
5
6
Moles of NaOH(aq)
0.08
0.07
0.06
0.05
0.04
0.03
Temperature Rise/◦C
6.2
9.7
13.2
15.7
11.7
8.7 Observations: The reaction that occurred was exothermic.

Results:
1. The graph of temperature rise/◦C vs. moles of NaOH(aq)/mol.was plotted and the end-point was found to be 0.051 mol.
2. Vol.=( mol./ molarity)*1000 = (0.051mol./ 1.92moldm-3)*1000 =26.56cm3
Volume of NaOH(aq) reacting at end-point = 26.56cm3

Vol.= total vol. of both sol. – vol. of NaOH(aq) = 50cm3 - 26.56cm3 = 23.44cm3
Volume of H2SO4(aq) reacting at end-point = 23.44cm3

3. Balanced Equation; H2SO4(aq) +2 NaOH(aq) Na2SO4(aq) + 2H2O(l) Mole Ratio; H2SO4(aq) : NaOH(aq) 1 : 2 Mol. = 0.051 mol/2 = 0.0255mol. Number of moles of H2SO4(aq) reacting at end-point = 0.0255mol
4. Molarity = (mol.*1000)/ vol. = (0.0255mol*1000)/ 23.44cm3 =1.089moldm-3 Concentration of H2SO4(aq) in FB1 = 1.089moldm-3

Discussion: The concentration of sulphuric acid in the FB1 solution was found to be 1.089moldm-3througth a thermometric titration. The graph temperature rise/◦C vs. moles of NaOH(aq)/mol. plotted, showed that the number of moles of NaOH(aq) reacting at the end-point of the reaction was 0.051 mol by drawing two intersecting best-fit lines. The point of intersection of the best-fit lines, shows the point of neutralization of the reaction. The graph also shows that with an increase in the number of moles of NaOH(aq) there was also an increase in temperature, suggesting that the number of moles of NaOH(aq) is directly proportional to the increase in temperature. Limitations for this experiment include possible heat loss from the experiment or heat gained from the environment. Also the thermometers used may not have been sensitive enough to give accurate temperature readings. In an effort to reduce these limitations the experiment could be done in a more controlled environment to obtain more accurate results.
Conclusion: The purpose of the experiment was to determine the concentration of sulphuric acid by thermometric titration which was found to be 1.089moldm-3.
References:
(2008) Thermometric Titration http://www.savitapall.com/thermochemistry/labs/THERMOMETRIC%20TITRATIONS.pdf

References: (2008) Thermometric Titration http://www.savitapall.com/thermochemistry/labs/THERMOMETRIC%20TITRATIONS.pdf