calorimetry Hess's Law Lab limitations???

[cassandra8462]

Hey guys,

I'm doing a lab in my SL Chemistry class called the Heat of Reaction/ Hess's Law lab. Basically we used a polystyrene cup as our calorimeter, and performed three reactions. Calculations were made to determine molar enthalpy. The target reaction was reaction 3 (-54.3 kJ/mol) , and reaction 1 and 2 were used to calculate the molar enthalpy of the target reaction (-50.8 kJ/mol). We then compared the values.

What are some limitations of this lab? I'm really stuck. Thanks in advance! (below I have posted the entire procedure)

1. Pour 200 mL of water into a polystyrene cup and record the temperature.

2. Measure out 4 grams of sodium hydroxide pellets and record the mass.

3. Pour the sodium hydroxide into the water and stir until dissolved. Record the temperature of the solution. Discard.

4. Pour 200 mL of 0.50M hydrogen chloride solution into a polystyrene cup and record the temperature.

5. Measure out 4 grams of sodium hydroxide pellets and record the mass.

6. Pour the sodium hydroxide into the hydrogen chloride and stir until dissolved. Record the temperature of the solution. Discard.

7. Measure 100 mL of 1.0M hydrogen chloride solution into a polystyrene cup.

8. Measure 100 mL of 1.0M sodium hydroxide solution into a 250 mL beaker.

9. Record the temperature of both solutions.

10. Pour the sodium hydroxide into the hydrogen chloride. Record the temperature of the solution. Discard.

[shellziess]

The most obvious limitation is the heat release... I mean your calculations will not capture all of the heat release even if you measure temparature change. Secondly make sure you include all the uncertainties of your measurements as these are also limitations and the rest are mostly human errors...