The Mind Soul

*Trial 1 (HCl* of unknown concentration):
?H per mol of H2O= 57.641 kJ/mol
?H= q = mC?T nH2O = ?H / ?H per mol of H2O
= (100.0g)( 4.184 J/?Cg)(34.0 ?C- 22.5?C) = 4.8116 kJ / 57.641 kJ/mol
= 4.811.6 J= 4.8116 kJ = 0.083475 mol
CHCl= n/V
= 0.083475 mol mol /0.0400 L
= 2.0869 mol/L
Average from trials 1&2 of unknown concentration of HCl= (2.0869 mol/L + 1.9962 mol/L) / 2
= 2.0415mol/L
Therefore, the concentration of the HCl is 2.0415mol/L
Discussion:
The last 2 trials carried out were using an unknown concentration of HCl (unknown #3). To find this concentration, the heat of reaction per mol of water formed determined from part is used. Since the NaOH is in excess, then the moles of HClwill equal the moles of water formed, as HCL disassociates completely in solutions. To obtain the moles of water formed for this reaction, the heat of reaction, which is calculated by multiplying the sum of the volumes of the base and acid with the specific heat capacity of water and the temperature change, is divided by the heat of reaction per mole of water formed (from part A). This gives the moles of HClthat was present in the solution. To find the concentration of HCl, this number of moles is divided by the volume used for the reaction, which in this case was calculated to be 2.0415mol/L.
There are many sources of error that may have occurred during this experiment. One could have been that the heat that was produced may have escaped to the surroundings such as the atmosphere or to the calorimeter itself, which would cause a less change in temperature, and therefore a smaller heat of reaction calculated. Another error that may have contributed is the fact that the specific heat capacity used (4.184 J/Cg) is not exactly the right specific heat capacity. Since it was assumed that the solutions specific heat capacity was that of waters, even though it did contain a few ions, which would have altered the calculations. Depending on if the real.