175 THER0368: Heat of Neucralization Post-Laboratory Questions (Use the spaces p

Question

175 THER0368: Heat of Neucralization Post-Laboratory Questions (Use the spaces provided for the answers and additional paper ecessary.) 1. A student was given only one graduated cylinder to use for this experiment. After using it to measure 50.0 mL of the assigned acid, the student failed to rinse or dry the cylinder before measuring out the 50.5 mL of the base. Would the calculated be higher, lower, or the same as the literature aHowten? Briefly explain this difference as a result of using only one graduated cylinder for the experiment for this experiment would affect the results. (1) A glass beaker was used instead of a pressed polystyrene cup. A pressed polystyrene top was used to cover the polystyrene cup after the acid and base solutions had been mixed. (2)

Explanation / Answer

1. If the student failed to rinse the measuring cyllinder after using it for acid solution, some part of base would be neutralized right in the cyllinder by the acid present. Therefore, the net moles of base added to the reaction would be lower. Less amount of acid would react with no added low amount of abse and release heat. The dHneutralization would therefore be lower than the literature dHneutralization value.

2. Effect of reaction parameters

(1) If a glass beaker (non-insulated container) is used instead of pressed polystyrene cup (insulated container), the calculated dHneutralization would be lower as some heat would be lost to the surrounding.

(2) No heat loss would occur, reaction would give better results.

3. The dHneutralization of HBr with NaOH and HNO3 with KOH are identical

(1) net ionic equation for both,

H+(aq) + OH-(aq) ---> H2O(l)

so both HBr and HNO3 have same active species H+.

(2) aqueous NaOH and KOH have both OH- which is seen in net ionic equation above.

(3) the dHneutralization for both reactions would be expected to be same as the net ionic reaction is the same for both. The other ions are just spectator ions,

complete ionic equation

H+(aq) + Br-(aq) + Na+(aq) + OH-(aq) ---> H2O(l) + Na+(aq) + Br-(aq)

and,

H+(aq) + NO3-(aq) + K+(aq) + OH-(aq) ---> H2O(l) + K+(aq) + NO3-(aq)

The common ions on both sides gets cancelled and we get samer net ionic equation for both so dHneutralization is also the same.

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