Question

Consider these possible sources of error described below. Briefly explain the effect of each on your calculated molar heats of neutralization. Indicate which item(s) of data would be in error and the effect (too large, too small or no effect). a. Step 9: You failed to adjust the temperature of the acid and base to the same temperature before you mixed them in Step 10.

Answer 1

For the calculation of the heat of neutralization you probably used the equation:

$q=m\cdot c\cdot \Delta T$

Where m is the mass of the whole system, c is the specific heat and delta T is the change in temperature, given by T_final - T_initial. The error in this case would be in the value of T_initial, since the temperature of the acid+base system immediately after mixing them is unknown, due to the fact that they were not at the same temperature to begin with. Had they been at the same temperature, we know that the initial temperature would be that value. The effect it will have on your result depends on which initial temperature you take, if the acid's or the base's. The real initial temperature after mixing them is somewhere in between the temperature of each component. Suppose your acid was hotter than the base. If you take the temperature of the acid as T_initial, the initial temperature used for the calculation is bigger than the real one, so delta T is smaller than the real one and the calculated heat ends up being smaller than the real one. Inversely, if you take the temperature of the base as T_initial, this value is lower than the real one, so the calculated delta T and, consequently, the calculated heat, will be higher than the real value.