Guide Questions

Experiment 1

Calibration of the calorimeter:

1. Give the net ionic thermochemical equation of the reaction used to calibrate the calorimeter. a. Is the reaction endothermic or exothermic?b. Which is the limiting reactant?c. How much (in moles) limiting reactant was used?d. How much heat was generated (or absorbed) by the reaction?

2. Relate the sign of the ΔT to the ΔH of the reaction used for calibration.3. What is the heat capacity of the calorimeter? Relate its sign to the sign of the ΔT.4. In the appendix, show the derivation to obtain the equation used to calculate the heat capacity of

the calorimeter.

Determination of Heats of Reaction:

5. Give the net ionic equation for each reaction.6. Determine the limiting reactant and the amount of the limiting reactant in each of the reaction

performed.7. Calculate for the theoretical and experimental enthalpy of each reaction.

a. Determine whether the reaction is endothermic or exothermic.b. Give the %error of your experimental values.

8. Relate the sign of ΔT to the sign of the experimental ΔH.9. For reactions 1 – 4, which pair gave the most and the least exothermic (or endothermic) reaction?

Explain the observation. (Use both the theoretical and experimental values to answer this)10. For reactions 5 and 6, which gave the most exothermic reaction? Why? (Use both the theoretical

and experimental values to answer this)11. For reactions 7 and 8, what are the solid products of the reaction? What is the theoretical yield of

each?12. Reaction 8 is a synthesis (combination) reaction. Using the theoretical ΔH of the reaction, deduce

the relative magnitude of the energy of bond breaking and bond formation during the reaction.13. In the appendix, show the equation used to determine the heats of reaction for reactions 1 – 6 and

reactions 7 and 8.

14. Tabulate the possible sources of errors and their effect to the following parameters: ΔT, Ccal and ΔH. Accompany each with a reason.

Source of Error Effect on ÄT Effect on Ccal Effect on ÄHSource Effect (Reason) Effect (Reason) Effect (Reason)

Experiment 2

1. Give the balanced equation for the observed reaction in the experiment.2. Describe the physical properties of the products produced and relate it to the balanced equation of

the reaction.3. What is the (approximate) Gibb’s Free Energy of the reaction observed? Assume that the reaction

temperature is about 1000K. Use the Ellingham diagram provided in the manual to calculate for this.

4. Why should the Mg ribbon be filed prior to use?5. What factors contributed for the slow/delayed ignition of Mg ribbons? Explain how each retarded

ignition.6. What is the possible side reaction in the experiment? Give the balance chemical equation for this

side reaction.7. What is the theoretical combined mass of the products in the experiment? Compare this to the one

obtained in the experiment. Account for any difference.8. What are the possible sources of errors in the experiment? Explain their effect to the yield.

Experiment 3

Determination of Rate Law of the Reaction Between Thiosulfate and Hydronium Ion

1. Give the balanced chemical equation for the reaction under study.2. Express rate in terms of the change in reactants and products with respect to time; d[]/dt.3. Of the species involved in the reaction, which chemical species served to determine the “end” of

the reaction? What is the physical manifestation of the “end of the reaction?4. Explain why the rate of reaction was approximated to be equal to 1/t.5. Discuss the significance of using beakers of the same diameter when the experiment was

performed. Determine the effect of not using beakers of same diameter to the rate of the reaction.

a.6. Discuss the significance of using the same timer when measuring the time it takes for the

reaction to be completed. Determine the effect of not using the same timer to the rate of the reaction.

7. Discuss the significance of having only one person to judge the completion of the reaction. Determine the effect of having multiple individuals judging the “end” of reaction.

8. Discuss the significance of adding the acid last in runs 1 – 3 and adding thiosulfate last in runs 4 – 6.

9. Determine the rate order with respect to the reactants in the reaction. Show in sample calculations the COMPLETE solution.

10. What does the rate order you calculate implies about the molecularity of the reaction? 11. Set-up the rate law. R=k[S2O3

2--]12. Based on the rate law, suggest a mechanism for the reaction between thiosulfate and hydronium

ion.

Temperature-dependence of Reaction Rate: The Arrhenius Equation

13. Based on the data obtained, how is temperature related to the rate of reaction? Explain the observed trend in the experiment using theories in kinetics.

Temperature-dependence of the reaction rate is mathematically shown in the Arrhenius equation. The Arrhenius is equation is given as

k = Ae-Ea/RT Since reaction rate is directly proportional to the rate constant, then an increase in the value of the k means an increase the reaction rate.

14. Explain why 1/t is taken to be the rate constant.15. Construct a –ln 1/t vs 1/T graph. Report the equation of the best fit line and the linearity

coefficient. What does the linearity coefficient suggest about the relationship of –ln 1/t with 1/T?16. Calculate for the activati

17. on energy of the system. Discuss the significance of the sign (+ or -) of the Ea and explain why is it so.

18. Determine ΔH of the reaction and construct an energy profile for the reaction.

Catalysis A: Reaction of Peroxysulfate (or Persulfate) with Iodide

19. Give the balance equation for the reaction between peroxysulfate and iodide. Hint: It is a redox reaction.

20. What is the role of Cu2+? Cu2+ acts as a catalyst, lowering the activation energy of the reaction thus, increasing the rate of the reaction.

21. What is the role of starch in the reaction? The starch reacts with iodide to form the blue-iodo starch complex which served as an indication of the completion of the reaction.

22. Draw an energy diagram for this exothermic reaction. Overlay the plot for the uncatalyzed reaction with the catalyzed one (use dashed lines).

Catalysis B: Autocatalysis of the reaction Between Acidified Permanganate and Oxalate

23. Give the balanced equation for the reaction of permanganate with oxalate. 24. Why was H2SO4 used to acidify the solution? What other acids can be used in replacement of

H2SO4? 25. What determined the “end” of the reaction? Aside from the one used in the experiment, what

(phenomeneon, etc) else would you use to signal the end of the reaction?26. Among the species involved in the reaction, which is the catalyst?27. Explain autocatalysis.

Experiment 4

Iron-Silver Equilibrium

1. Give the balanced chemical equation for the reaction between Fe2+ and Ag+.2.3. Why should centrifugation be done for this part of the experiment?4. Give the balanced chemical equation for the reaction of Fe2+ with Fe(CN)6

3-.a. What is the color of the product?b. What does this proved regarding the reaction between Fe2+ and Ag+?*

5. Give the balanced chemical equation for the reaction of Fe3+ and SCN-.a. What is the color of the product?b. What does this prove regarding the reaction between Fe2+ and Ag+?*

6. Give the balanced chemical equation for the reaction between Ag+ and Cl-.a. What is the color of the product?b. What does this prove regarding the reaction between Fe2+ and Ag+?*

7. What is the range of Keq for this reaction?

*Has the same reason

Copper-Ammonia Equilibrium

8. Give the balanced chemical equation for the reaction between Cu2+ and NH3.9. At the beginning of the reaction between Cu2+ and NH3:

a. What is the color of the precipitate formed?b. What is the identity of the precipitate formed?c. Explain how this precipitate formed.

10. When the precipitate dissolved, what is the color of the solution? What species is responsible for this?

11. Explain how the addition of HCl decolorized the solution.12. Give the balanced equation for the reaction responsible for the shift in equilibrium for this

system.13. Compare the number of drops of HCl added to the number of drops of NH3 needed. Explain the

relationship of the number of drops of the two reagent.

Chromate-Dichromate Equilibrium

14. What is the color of chromate solution? of dichromate solution?15. Which species (CrO4

2- or Cr2O72-) changed color when acid was added? when base was added?

16. Why was H2SO4 used to acidify the solutions?17. Give the balanced chemical equation for the conversion of chromate to dichromate.18. Give the balanced chemical equation for the conversion of dichromate to chromate.19. Use your answer in 15 and 16 to explain your observation in 14.20. Based on your observation in 14, which species is stable under acidic condition? under basic

condition?

Iron Thiocyanate Equilibrium

21. Give the balanced equation for the reaction between Fe3+ and SCN-.22. To which direction the equilibrium shifted when (a) Fe3+, (b) SCN- and (c) NaCl was added?

Explain your answer based on your observation during the experiment.23. For 21c, what reaction caused the observed shift in equilibrium?

Cobalt-Cobalt Chloride Equilibrium

24. Give the balanced chemical equation for the reaction between Co2+ and Cl-.25. What is the color of Co2+? of CoCl4

2-?26. Based on your answer in 24, explain the observed color in the experiment before the solution was

heated.27. Is the reaction in 23 endothermic or exothermic? Defend your answer.

Note: Balanced chemical equation = Net ionic equation

Experiment 5

Solution Preparation

1. Why should the solutions be prepared with 0.10M HCl used as solvent?a. What will happen to Fe3+ if the solution was not prepared using 0.10M HCl?b. Give the balanced equation for the 1st hydrolysis of Fe3+.c. What is the color of the product of 1st hydrolysis of Fe3+?d. What is the effect of the product of 1st hydrolysis to the absorbance of the solution?

Determination of Analytical Wavelength

2. Why should the solution with highest concentration be used to determine the analytical wavelength?

3. What was the analytical wavelength of FeSCN2+?4. Relate the analytical wavelength to the color of the solution. Hint: Use a color wheel.5. Why should we measure absorbance at the analytical wavelength?

Calibration

6. What is the importance of the blank solution?7. Why is KSCN added in large excess?8. What is the concentration of FeSCN2+ for each solution?9. Determine the corrected absorbance of the solutions. The corrected absorbance is the difference

between the absorbance of the analyte solution and the blank.10. Plot the corrected absorbance of the solution against the concentration of FeSCN2+. Determine the

equation of the best fit curve.11. Using the slope of the best fit curve, determine the molar absorptivity or the molar extinction

coefficient, ε of FeSCN2+. The path length is 1cm. Compare the value you obtained to the theoretical value.

Determination of Unknown FeSCN2+ concentration

12. Why should the concentration of KSCN used be 0.002M instead of 0.20M which was the concentration used during calibration?

13. Why was another blank solution prepared and used for this part of the experiment?14. Calculate for the corrected absorbance of the unknown solutions.15. Determine the concentration of FeSCN2+ of each solution using the equation of the best fit curve.

The concentration you will get here is the equilibrium concentration of FeSCN2+.

Determination of Kf of FeSCN2+

16. Determine the initial concentration of Fe3+ and SCN- of each unknown solution.17. Calculate for the equilibrium concentration of Fe3+ and SCN-.18. Show the expression needed to calculate for Keq or Kf of FeSCN2+.19. Report the average Keq or Kf calculated and compare it to the range of the theoretical values for

Keq of FeSCN2+.

Sources of errors

20. Determine all possible sources of errors. Identify whether the error is determinate or indeterminate. Also, if the error is determinate, identify if it is systematic, random or gross error. Report in tabulated form.

Experiment 8

Preparation of Ca(OH)2

1. Write the balanced chemical equation for the synthesis of Ca(OH)2. What is the relationship of its Keq to Ksp?

2. Why was NaOH added in excess?

3. Why was Ca(NO)3 added dropwise with continuous mixing?4. Why was the precipitate washed with distilled water? with 95% ethanol? with acetone? Why

should the order be like that?

Preparation of saturated Ca(OH)2 solution

5. What was the indicator that a saturated solution had already been prepared?6. Why is it important to filter the solution?

Titrimetric Analysis

7. What is the initial color of the solution when phenolphthalein was added? Why is it so?8. What is the color at the endpoint of titration?

Data Analysis

9. Express Ksp in terms of the molar solubility of Ca(OH)2.10. Solve for the [OH-] in each solution.11. From the computed [OH-], solve for the [Ca2+]. This value is your molar solubility.12. From the data obtained from saturated solution with water as solvent, solve for the Ksp of the

Ca(OH)2. Compare the experimental to the theoretical value of Ksp.13. Compute for the ionic strength of each solution containing KCl.14. Plot molar solubility against ionic strength of the solvent. DO NOT perform linear regression.

What can you say about the trend? Include only the solutions with KCl. DO NOT include data for water in your plot.

15. Compare the solubility of Ca(OH)2 in 0.1M Ca(NO3)2 solution to the solubility in water. Provide an explanation to the experimental result.

16. Calculate for the theoretical solubility of Ca(OH)2 in 0.1M Ca(NO3)2 and compare it to your experimental data.

17. Discuss common ion and diverse ion effect.

18. Give all possible sources of errors, determine which parameter will be affected, and determine whether it would give a positive or a negative error. Tabulate.

Experiment 9

Cu(OH)2(s) Cu2+ + 2OH- System

1. Give the balance chemical equation for the synthesis of Cu(OH)2.2. After centrifugation and decantation, why was NaOH added?3. Write the reaction happening in each of the test tube.4. Compute the K for each net reaction.5. Does your observation agree with your computed K of the net reaction? Explain your answer.

NaCl(s) NaCl(aq) System

6. Between 95% ethanol and HCl, which gave more precipitate? Why?7. By what virtue did ethanol enhance the recrystallization/precipitation of NaCl?8. By what virtue did HCl enhance the recrystallization/precipitation of NaCl?

9. Explain the observed dissolution of MgSO4 in NaCl. Is this always true for any saturated salt solution?

Experiment 14

Reaction between Na2SO3 and KMnO4 in Various Media

1. Give the balanced redox equation (give the oxidation half reaction, reduction half reaction and the net reaction) of each reaction.

2. Determine which product is responsible for the observed color for each reaction.

Reaction between FeSCN2+ and Zn

3. Give the balanced redox equation for the reaction between FeSCN2+ and Zn.4. What is the proof that a reaction happened between FeSCN2+ and Zn?

Reaction between Fe4[Fe(CN)6]3 and Zn

5. Which Fe (the counter ion or the one coordinated to CN) was reduced by Zn? Why?6. Give the balanced redox equation for the reaction between Fe4[Fe(CN)6]3 and Zn.