Department of Chemistry and Chemical Technology: 1274849

Data Sheet

1. Overall Stoichiometric Equations

2Cu²⁺_(aq) + 4I^–_(aq) → 2CuI_(s) + I_2(aq)

           white solid          brown

2S₂O₃^2-_{(aq) +} I_2(aq) → S₄O₆^2-_(aq) + 2I^–_(aq)

  colourless                 brown           colourless                 colourless

2 Cu²⁺_(aq) + 4 I^–_(aq) + 2 S₂O₃^2-_(aq)  + I_2(aq) → 2CuI_(s) + I_2(aq) + S₄O₆^2-_(aq) + 2I^–_(aq)

2Cu²⁺ _(aq) + 2I^– _(aq) + 2S₂O₃^2-_(aq) → 2CuI_(s) + S₄O₆^2-_(aq)

• Results and Observations

Unknown No.: 40

Concentration of standard Na₂S₂O₃ solution 0.0206 M

         Trial 1         Trial 2     Trial 3   

Initial burette reading, mL   0.48             10.32        20.21      

Final burette reading, mL         10.32           20.21        30.11        

Volume of Na₂S₂O₃ used, mL 9.84             9.89          9.90      

Amount of Na₂S₂O₃ used, mol           0.000303      0.000204              0.000204    

Amount of Cu²⁺ in unknown sample, mol               0.000303       0.000204             0.000204   

Volume of original Cu²⁺ solution used, mL       10.00          10.00                    10.00      

Concentration of Cu²⁺ in original solution, M              0.0303          0.0204             0.0204       

Average Concentration of Cu²⁺, M         0        0.0237M

Calculations

1. Calculate the number of moles of Na₂S₂O₃ used in each titration.

Trial 1: 9.84mL Na₂S₂O₃  = 0.000202704mol Na₂S₂O₃

     = 0.000303 mol Na₂S₂O₃

Trial 2: 9.89mL Na₂S₂O₃  = 0.000203734mol Na₂S₂O₃      = 0.000204mol Na₂S₂O₃

Trial 3: 9.90mL Na₂S₂O₃  = 0.00020394mol Na₂S₂O₃        = 0.000204mol Na₂S₂O₃

• Determine the number of moles of Cu²⁺ in each sample.

Trial 1: 0.000202704mol Na₂S₂O₃  = 0.000202704mol Cu²⁺= 0.000303 mol Cu²⁺

Trial 2: 0.000203734mol Na₂S₂O₃  = 0.000203734mol Cu²⁺ = 0.000204mol Cu²⁺

Trial 3: 0.00020394mol Na₂S₂O₃  = 0.00020394mol Cu²⁺ = 0.000204mol Cu²⁺

• Calculate the original concentration of Cu²⁺ in each sample.

Trial 1: 0.000303 mol Cu²⁺ / (10.00mL) = 0.0303M Cu²⁺

Trial 2: 0.000204 mol Cu²⁺   / (10.00mL) = 0.0204M Cu²⁺

Trial 3: 0.000204 mol Cu²⁺   / (10.00mL) = 0.0204M Cu²⁺

• Calculate the average concentration of the original Cu²⁺ solution.

 = 0.0237M Cu²⁺

References

Han, N. S., Li, H. K., Sin, L. C., & Sin, K. P. (2018). The evaluation of students’ written reflection on the learning of general chemistry lab experiment. MOJES: Malaysian Online Journal of Educational Sciences, 2(4), 45-52

Lee, N. (2020). CHEM 124-102: General Chemistry Lab

Stephenson, N. S., & Sadler-McKnight, N. P. (2016). Developing critical thinking skills using the science writing heuristic in the chemistry laboratory. Chemistry Education Research and Practice, 17(1), 72-79