Calorimetry 2j3214

Calorimetry: Determination of Heats of Solution CHEM 1001/1005 (pages: 47-57)

2012

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Goals • Measure the heat capacity (Ccal) of a constantpressure calorimeter • Determine the heat of solution (ΔHsol’n) of 

(anhydrous) Sodium acetate (Na2C2H3O2)



Sodium acetate trihydrate (Na2C2H3O2•3H2O)

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Theory: First Law of Thermodynamics • Heat (q) of the universe is ZERO quniverse = 0 qwarm + qcool + qcalorimeter = 0 qreaction + qsolution + qcalorimeter = 0 So, and

qcalorimeter = - (qwarm + qcool ) qreaction = - ( qsolution + qcalorimeter ) = ΔHreaction because ΔP = 0

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Theory: Heat Capacity vs. Specific heat • Heat capacity (C) qcalorimeter = - (qwarm + qcool ) = Ccalorimeter  T

• Specific heat () q = m  water  T = m  4.184 J/(g* C)  T (q: qwarm, qcool, qsolution) 4

Apparatus Note: When shaking the calorimeter, DO NOT allow the GoLink device to move around. It may get damaged!

Hold the calorimeter by the tubing when stoppering/removing temperature probe.

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Procedure: I. Calibrate the calorimeter (3 trials) • Set up the calorimeter (get warm water heating to save time!) • Collect water (15.0 mL) to calorimeter, record T1i • Warm up water to 80oC, collect 20.0 mL into a Logger Pro Measurements styrofoam cup, to record T2i “Collect” (at the start of trial) Shake 60s • Pour them to calorimeter, record Tf Wait 100s Record temperature

Note: Equations on P.52 for calculation of CCalorimeter Volume (mL) Mass (g) T (˚C) Cool (room temperature water) 15.0

15.0

T1i

Logger Pro

Warm (heated water)

20.0

T2i

Regular thermometer

Tf

Logger Pro

Calorimeter (mixed water)

20.0

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Procedure: II. Measure heat of solution • Dry calorimeter and thermometer • Collect water (35.0 mL), add to calorimeter, record Ti • Weigh (use weighing bottle) NaC2H3O2 (1.5000 g). Do this quickly!!

• Transfer NaC2H3O2 to calorimeter, record Tf • Repeat with 2.0000 g, 2.5000 g, 3.0000 g of NaC2H3O2  Repeat for NaC2H3O23H2O (have one table for each salt)

Trial Mass (g) 1

1.5000

2

2.0000

3

2.5000

4

3.0000

Ti (˚C) Tf (˚C)

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Pop Question: What’s wrong with this picture?

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Things to … • NaC2H3O2 is hygroscopic, weigh & transfer it fast • Record exact mass (analytical balance) and volume (graduated cylinder) • Volume must be exactly what is prescribed • Dry calorimeter & thermometer before each run • Distilled water should be room temperature. Can use bottle. • Uncertainty of top-loading balance ( 0.0001 g), 50mlgraduated cylinder ( 0.1 mL), thermometer ( 0.2oC) • Molar heat of solution of sodium acetate (-17.3 KJ/mol) and sodium acetate trihydrate (19.7 KJ/mol) at 25oC • Clean up and inventory your station before you’re signed out. 9

After-lab Write-up DUE: Next lab Period Calculation 1. 2. 3.

Heat capacity of your calorimeter Molar heat of solution of sodium acetate and sodium acetate trihydrate for each experiment you carried out. Tabulate the values. (Eight values in total) Average value for each molar heat of solution, and compare them with the accepted values. Calculate the relative spread and relative error

Discussion - Around one paragraph, discussion high/low results and questions 4 and 5 on lab manual See P.57

Conclusion - One or two sentences, summary of all results

Quality of discussion and conclusion (what we look for in these sections) 1. 2.

In discussion – list two reasons why results are high/low and answers of questions 4&5 In conclusion – report the heat capacity of your calorimeter, average ΔH values, relative errors, relative spreads 10

2. Molar Heat of solution, ΔHm

ΔHm= - [ qsolution + qcalorimeter ]/moles of Na2C2H3O2 = - [ (msolution*ρsolution* ΔTsolution) + (Ccal * ΔTcal) ] moles Na2C2H3O2 Note: msolution = msalt + mwater ρsolution = 4.184 J/(g*°C) ΔT = Tfinal - Tinitial 3-iii. Relative Error: | Accepted value - Experimental value | X 100% (a.k.a. % Error) Accepted value 11