Expt10, Thermochemistry
Name: ______
Lab Partner:______
Date:______[J1]
Introduction[J2]
Part A
Determination of Heat Capacity of the Calorimeter
Initialtemperature of calorimeter and 50 mL cold H2O (Tcold): ______
Initial temperature of 50 mL warm H2O (Thot) : ______
Table 1: Time vs temperature data: Heat Capacity of the Calorimeter
[Insert a suitable table here.]
Plot Temp (oC) y vs. Time (s) x. Extrapolate the graph back to the y axis to calculate Tfinal, the final temperature of the calorimeter and the contents.
Inert the (excel or equivalent) plot showing the extrapolation, don’t forget title, axes labels, units and trendline.[J3]
Calculations
-Heat lost by hot water = heat gained by cold water + heat gained by calorimeter
[comment: note that you assume that the initial temperatures of the calorimeter and of the cold water are the same.]
-(mL hot water x 1.00 g/mL x ∆Thot x 4.18 J/g oC) = (mL cold water x 1.00 g/mL x ∆Tcold x 4.18 J/g oC) + (∆Tcold x Ccal)
This equation can be rearranged to solve for Ccal the heat capacity of the calorimeter
If you obtain a negative value for Ccal assume that the value of Ccalis zero…..[J4]
[…..comment: but, if you do need to assume the heat capacity of the calorimeter is zero, mention this in the discussion and comment on why you think this assumption was necessary.]
Show all your calculations of Ccal[J5]
Part B
Determination of Heat of Neutralization
NaOH(aq) Molarity: ______HNO3(aq) Molarity: ______
Initial temperature of 50 mL NaOH(aq) and Calorimter (Tb): ______
Initial temperature of 50 mL HNO3(aq) in gradcylinder (Ta) : ______
Table 2: Time vs temperature data: Heat of Neutralization[J6]
[insert a suitable table here]
Plot Temp (oC) y vs. Time (s) x. Extrapolate the graph back to the time at which the liquids are mixed to calculate Tfinal the final temperature of the calorimeter and the contents.
Insert the (excel or equivalent) plot showing the extrapolation, units, titles, labels and trendline equation.[J7]
Calculations
∆Tacid= Tfinal- Ta∆Tbase= Tfinal– Tb
-q neutralization = q solution
q solution = heat gained by acid + heat gained by base + heat gained by calorimeter
q soln = (mL acid x 1.00 g/mL x ∆Tacid x 4.18 J/g oC) + (mL base x 1.00 g/mL x ∆Tbase x 4.18 J/g oC)+ (∆Tbase x Ccal)[J8]
Part C
Determination of Heat of Reaction
Mass of CuSO4.5H2O used : ______use the analytical balance to weigh approximately 5 g[CC9]
Mass of Zinc used : ______use the analytical balance to weigh approximately 6.5 g[CC10]
Measure as accurately as possible 95 mL of Distilled Water.[CC11]
Transfer the CuSO4.5H2O to the 95 mL of distilled H2O in the calorimeter and dissolve completely.[CC12]
Initial temperature of 95 mL CuSO4.5H2O solution and Calorimter (Tinitial): ______[J13]
Add the Zinc to the calorimeter and begin counting time. Continue to measure the temperature at least 2 minutes after the maximum temperature has been reached.[J14]
Table 3: Heat of Reaction[J15]
[insert a suitable table here.]
*If your reaction has not reached a maximum temperature after 8 minutes. Stop and repeat.*[J16]
Plot Temp (oC) y vs. Time (s) x. Extrapolate the graph back to the time at which mixing uccurred to calculate Tfinal the final temperature of the calorimeter and the contents.[J17]
Insert the (excel or equivalent) plot showing the extrapolation, trendline, units, titles and axes labels[CC18]
Calculations[J19]
∆T= Tfinal– Tinitial= ______- ______
∆T = ______
Zn(s) + CuSO4(aq) → Cu(s) + ZnSO4(aq) + heatNote the stoichiometry
- qrxn = heat gained by ZnSO4(aq) (I) + heat gained by Cu(s) (II)+ heat gained by excess Zn(s) (III) + heat gained by calorimeter(IV)
- qrxn = (I) + (II) + (III) + (IV)
(IV) Heat gained by calorimeter= Ccal x ∆T = ______oC x ______J/oC =
(II) Heat gained by Cu(s)
mol of CuSO4.5H2O =mass used ______g x 1 mol= ______mol*
249.69 g
mol copper produced = ______mol
The Heat Capacity of both Copper and Zinc is 25 J/moloC
Heat gained by copper = ______mol Cu x 25 J/moloC x ∆T =
(III) Heat Gained by excess Zinc
mol zinc added = mass used ______g x 1 mol= ______mol
65.37 g
molzinc reacted = mol copper produced = ______mol
moles excess zinc = mol zinc added – mol zinc reacted = ______mol
Heat absorbed by excess zinc = ______mol x 25 J/moloC x ∆T =
(I) Heat gained by ZnSO4 solution
mol of ZnSO4 produced = mol of CuSO4.5H2O used = ______mol see * above
Mass of ZnSO4 produced = ______mol x 161.43 g= ______g ZnSO4
1 mol
mol water from hydrate (5H2O) = ______mol ZnSO4 x 5 = ______mol
mass of water from hydrate = ______mol x 18.02 g= ______g H2O from hydrate
1 mol
Mass of water added to calorimeter = (95) g______g[J20]
Total mass of ZnSO4 solution = ______g + ______g from hydrate + ______g ZnSO4
= ______g
Heat gained by ZnSO4 solution = ______g x 3.975 J/g oC x ∆T =
Therefore qrxn = - [(I) + (II) + (III) + (IV) ][J21]= =
∆Hrxn = ___ qrxn______[J22]=
mol CuSO4.5H2O
Make sure sign is correct for the exothermic reaction
Discussion
Calculate the actual ∆Ho for the copper/zinc reaction using the data below, compare it to your result. Calculate your percent error. Comment and include 3 sources of error. You have calculated the heat absorbed by the copper and the zinc separately; can you think of a simpler way to get the same final value?
The standard enthalpies of formation of Zn2+(aq) and Cu2+(aq) from zinc and copper metals are -152 kJ/mol and 64.4 kJ/mol respectively. Use this data to calculate the ∆Ho the standard enthalpy of the reaction:
Zn(s) + Cu2+(aq) → Cu(s) + Zn2+(aq)
Conclusion
Summarize the results of all three parts.
1
[J1]Use a nice title page…better
[J2]What are you going to do and why are you doing it. Add a couple of sentences outlining what you expect the results to be.
[J3]Delete my comments, as always, include graph as the appendix. Don’t forget how to calculate Tfinal, extrapolating the few points after the max temp back to the y axis
[J4]Check you didn’t do it wrong first before you assume this.
[J5]You can leave in the first equation in bold but the rest of the calculation should be your data. Don’t forget to include the correct units which your equation should spit out.
[J6]Make it more descriptive.
[J7]Delete my comments, as always, include graph as the appendix. Don’t forget how to calculate Tfinal, extrapolating the few points after the max temp back to the y axis
[J8]Remember the correct sign for the heat of neutralization is it exo or endothermic? Convert it to kJ and then divide it by the mol of base reacted to give an answer in units of kJ/mol
[CC9]delete
[CC10]delete
[CC11]delete
[CC12]delete
[J13]Leave this in and fill in the blanks
[J14]delete
[J15]jazz up the title heat of reaction for what?
[J16]Delete from your report
[J17]It is important that only use the immediate 6 or 7 points after Tmax to extrapolate back to the y axis
[CC18]delete
[J19]I’m leaving these in, make sure you understand all the steps. Fill in the blanks if you like or do your own calculation if you prefer and delete all mine.
[J20]Check this and get it right and then put it in the first space in the equation below. Your total mass should be around 100 g
[J21]Add up all the parts I thru IV the qrxn will be this value with a negative sign
[J22]Don’t forget this will be negative