Wow, I love the new look of the forums - awesome! Anyway, I have some questions on calorimetry which I've tried, but I'm not sure I'm doing it right. I'd appreciate any help.
We did a lab on the heat of neutralization for an acid-base reaction. Anyway, these were my results:
- volume of acid (HCl) - 50mL
- temperature of acid - 20.9 C
- volume of NaOH - 50mL
- temperature of NaOH - 20.2 C
- exact molar concentration of NaOH - 1.0 mol/L
- maximum temperature from graph (we had to make a graph of our results) - 27.5 C
- Average initial temperature of acid + base: (20.2 + 20.9)/2 = 20.6
- Temperature change: 27.5 - 20.6 = 6.9
- Volume of final mixture: 50 + 50 = 100mL
- Mass of final mixture (assume density of solution is 1g/mL): (1)(100) = 100g
- specific heat of mixture(given): 4.18J/g C
Here's the part I'm not sure of:
- Heat evolved: (4.18)(100g)(6.9) = 2884.2 J
- Amount of OH- reacted:
HCl + NaOH --> NaCl + H2O
100g NaCl + H2O x 1 mol x 1 mol NaOH x 1 mol OH-
76.46g x 1 mol x 1 mol NaOH
= 1.31 mol OH- ??
- Amount of H2O formed:
1.31 mol NaOH x 1 mol H2O
1 mol NaOH
= 1.31 mol H2O ??
- Heat evolved per mole of H2O, (heat of neutralization)
heat of neutralization = - Cp(H2O) x combined masses (acid + base) x change in temperature
= - (4.18)(100g)(6.9) = -2884.2 J
I know there's something fishy going on there, please *delete me*
1. A thermometer labeled as being miscalibrated at the factory – the freezing point of water reaches 1.2 ºC and the boiling point of water reads 101.2ºC at standard pressure. But, because you are in a hurry and the thermometer is the last one available, you decide to go ahead and use it in the experiment, recording the temperatures as they appear on the thermometer. How ill the use of this thermometer affect the determination of the specific heat of the metal?So does it just affect the temperature by 1.2ºC? or does it affect it by something else? Then again, it probably wouldn't affect it at all, because change in temperature would still be the same, right?
2. The calorimeter, although a good insulator, absorbs some heat when the system is above room temperature. The consequence of this heat loss from the system is accounted for in the temperature extrapolation f the data. Describe an experiment that could be used to calibrate the calorimeter by measuring this heat loss. I have NO idea about this one... hints, please?
Thanks again for all the help. I love you guys!