The possible source of error in this part of the experiment was the imperfect

# The possible source of error in this part of the

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The possible source of error in this part of the experiment was the imperfect transfer of the Na 2 CO 3 solid from the electrical balance to the beaker. After the mass of the Na 2 CO 3 was measured, the solid was transferred to the beaker. However, Na 2 CO 3 solid might slide down from the filter paper during the transfer process and the Na 2 CO 3 concentration in the solution might have been lower than the recorded value. Therefore, the concentration of HCl might also have been over estimated. In order to measure the K sp of borax, borax was dissolved in water at three different temperatures until saturation was reached. Then 5 mL of the borax solution at different temperature was titrated with standardized HCl solution and the volume of the titrant was record until the indicator showed a distinct color change. Then the concentration of the borate anion was
calculated. According to the equilibrium expression K sp = [Na + ] 2 [Borate 2- ], the K sp can be calculated by Ksp = 4 * [borate anion] 3 . 1 K sp , as a function of the temperature, increased as the temperature increased. When the temperature was 283.1, the K sp was 0.0035. When the temperature was 293.1, the K sp was 0.0105. When the temperature was 293.1, the K sp was 0.0105. There was linear relation between 1/T and Ksp and the expression was y = -5939.5x + 15.472 with a R 2 value of 0.94025. The linear relation between the 1/T and K sp validate the thermodynamic equation that H o – TS o = -RTlnK sp . The sign of Δ H o was positive and this means that the enthalpy of the reaction was  positive and  the reaction was endothermic. When a reaction is endothermic, heat is absorbed by  the system from the surroundings. The positive  Δ H o  shows that the reaction was not enthalpy  favored. The sign of  Δ S o was also positive and the entropy of the reaction was increasing. The products will have a higher randomness than the reactants. The calculated   Δ H o was   49.38 kJ / mol  and the literature value is 110 kJ/mol. The  calculated   Δ H o was lower than the literature value.  The calculated   Δ S o was   126.8 J / mol  and the  literature value is 380J/mol. The calculated   Δ H o was lower than the literature value. The  difference between the literature values and the calculated  values of Δ H o and Δ S o could have been caused by the following sources of erors. Errors in these numbers result from the accumulation of errors in the first part of and  errors in this part of the experiment. In part A, the possible source of error was the  imperfect transfer of the Na 2 CO 3 solid from the electrical balance to the beaker. This will cause the error in

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• Spring '11
• Dr.JohnZhang