CHEM 131L- EXP 13 - The questions and answers for post lab. PDF

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The questions and answers for post lab....

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Calorimetry; Experiment 11 Zor, Julianna ID: 0635183 CHEM 131- 103 Dr. H. Sobhi

DATA & CALCULATIONS 1. Part A: Create one typed table that concisely presents the observations and answers to the questions in part A. Data for both calcium chloride and urea should be in the table.

Mass (g)

Temp?

Observations

Conclusion

CaCl2

1.019 g

Increase

Warm

Exothermic

CaCl2

1.018 g

Increase

Warm

Exothermic

Urea

1.03 g

Decrease

Cold

Endothermic

Urea

1.019 g

Decrease

Cold

Endothermic

2. Part B: a. Show one set of typed calculations for the following values: m soln ,  T soln , q soln , q cal , q neut , mole of the limiting reactant and molar q neut . If you performed multiple trials, only show calculations for one trial. TRIAL 1: m soln: 45 g + 50 g= 95 g  T soln: 29.3 C – 22.6 C = 6.7 C q soln : -2800.47= -(qsoln + 137.35 J) = 2663.12 J q cal = 20.5 J/oC x (29.3 -23.7)oC = 137.35 J q neut= -(qcal – qsol) -> -[(20.5 x 6.7) – (95 x 4.184 x 6.7)] -> (-137.35 – 2663.116) -> -2800.47 KJ mole of the limiting reactant: .875= 1/.045 = .039 mol and molar q neut= (-2800.47/.039)/ 1000= -71.8 J/ mol

b. Create a table of just the calculated values listed above, displaying each value with proper units, mathematical sign and correct number of significant figures. Report the individual values for all trials in this table, as well as the average molar q neut.

m soln

 Tsoln

q soln

q cal

q neut

mole of the limiting reactant

molar q neut

Trial 1

95 g

6.7 O C

2663.12 J

137.35 J

-2800.47 KJ

.039 mol

-71.8 J/mol

Trial 2

95 g

6.9 O C

2742.61 J

141.45J -2884.06 KJ

.039 mol

-73.95 J/mol

Trial 3

95 g

7.8 OC

3100.34 J

159.9

.039 mol

-83.60 J/mol

-3260.24 KJ

Avg q neut: -76.45 J/mol QUESTIONS – All answers should be typed and given in complete sentences unless otherwise indicated. 1. Write the chemical equation for the reaction in part B and give the molar heat of reaction. Based on the data, is the reaction in part B exothermic or endothermic? Explain your answer. As part of your answer, explicitly state from where and to where the heat flowed during the reaction. NaOH aq + HClaq -> H20l + NaClaq molar heat of reaction= -2800.47/.055 moles /1000= -50.92 -50.92 KJ/mol + -71.8 KJ/mol= -122.72 KJ/mol It is exothermic, because the answer is negative which means it is releasing heat. The heat flowed from the system into the surroundings. 2. What would happen to the measured data (temperature specifically) if lower concentrations of chemicals were used in part B? Explain your answer.

If there are lower concentrations, the reaction would proceed slower which makes the temperature decrease. 3. F or each of the following components from part B, indicate whether they are part of the system or the surroundings. a. Styrofoam cups: surroundings b. Thermometer: surroundings c. Hydrochloric acid: system d. Sodium hydroxide: system e. Water from the sodium hydroxide solution: system f. Water product from the reaction: system 4. Give two possible sources for error that might have occurred during part B. Your answer cannot be based on just ‘human’ error (examples: calculation error, not following directions). Instead think about how the experimental set - up might lead to error. One possible source of error is that the lid and probe was not securely attached. This could influence the temperature of the inside, because the outside room temperature would have an effect on the reaction. Also another source of error is if there were holes in the Styrofoam cup. If there were holes, the reaction would spill out and the room temperature would influence the reaction’s temperature....