Inorganic

EXPERIMENTAL

For Cu2HgI4, 0.164 grams of KI (dissolved in approximately 5 mL of H2O), 0.229 grams of HgI2 were added to a 25 mL Erlenmeyer flask. The solution was then shaken and set aside. Following this, 0.226 grams of CuSO4 and 0.507 grams NaCl (dissolved in 2 mL of H2O) were added to a separate 25 mL Erlenmeyer flask, forming a green solution. 0.109 grams of NaHSO3 were added, turning the solution to a yellow color. A Pasteur pipet was then used to transfer the copper salt solution to the mercury iodide – potassium iodide solution and then the solution was iced for a few minutes. Finally, the solution was vacuum filtrated, washed with ice water, and weighed. Then the thermochromatic temperature was taken.

The second part of the experiment involved Ag2HgI4. First, the mercury iodide – potassium iodide was prepared similarly, this time using 0.229 grams of HgI2 and 0.167 grams of KI. Then, the two procedures diverge, and instead of CuSO4, 0.192 grams of AgNO3 (dissolved in 5 mL of H2O) is prepared in a separate flask. Then, a Pasteur pipet was used to transfer the mercury iodide – potassium iodide solution to the AgNO3 solution. The solution was then iced for a few moments before being vacuum filtered. The precipitate was then weighed and the thermochromatic temperature was taken.  After all of this, the final procedure was performed – measuring the ionic conductivity of Ag2HgI4. This was done by obtaining a Pasteur pipet and inserting two pieces of copper wire – one from the bottom narrow opening, the other from the top, wider opening – between ½ of the precipitate of Ag2HgI4 formed earlier. Then a multimeter (adjusted to 2MW) was used to measure the electrical resistance of the two electrodes as the precipitate was heated.

RESULTS

Equations

2NaCl + CuSO4*5H2O  ------>  CuCl2+ Na2SO4 + 5H2O

2KI + HgI2 -------> K2HgI4

2AgNO3 + HgI42- -------> Ag2HgI4+ 2NO3-

2CuCl2 + HgI42- --------> Cu2HgI4 + 4Cl-

Sample Calculations

Theoretical Yield:

K2HgI4 formed (for copper):
                (0.164)/(166) =  9.88E-4 mol of KI have
           (0.229)/(454) = 5.044E-4 mol of HgI2 have * 2 = 1.01E-3 mol KI needed
            KI is the limiting reactant
            4.94E-4 mol of K2HgI4

CuCl2 formed:
        (0.507)/(58.44) = 8.68E-3 mol of NaCl have * ½ = 4.34E-3 mol of CuSO4 needed
        (0.226)/(249.6) =  9.054E-4  mol of CuSO4 have
        CuSO4 is the limiting reactant
        (9.05E-4)(134.45) = 0.12 grams of CuCl2or 9.05E-4 mol of CuCl2

Cu2HgI4 formed:
        CuSO4 is the limiting reactant.
        (9.05E-4/2)(835.3) = 0.378 grams of Cu2HgI4

K2HgI4 formed (for silver):
                (0.167)/(166) =  1.00E-3 mol of KI have * ½ = 5.00E-4 of HgI2 needed
           (0.229)/(454) = 5.044E-4 mol of HgI2 have * 2 = 1.00E-3 mol KI needed
            KI is the limiting reactant
            5.00E-4 mol of K2HgI4

Ag2HgI4 formed:
        (0.192)/(169.87) = 1.13E-3 mol of AgNO3
        K2HgI4 is the limiting reactant
        (5.044E-4)(923.95) = 0.466 grams

Percent Yield

        Cu2HgI4:
                0.469/0.412 *100 = 113.83%

        Ag2HgI4:
                0.660/0.466 * 100 = 141.6%

DISCUSSION

        The percent yields for Cu2HgI4 and Ag2HgI4 are 127.07% and 141.6% respectively. They are impossibly high due to the fact that the weights of the precipitates were taken before waiting one week…therefore, it’s likely that there is a lot of water weight present. The thermochromatic temperature ranges, done a week later when the products were dry, were highly accurate. The literature accepted values of Cu2HgI4 and Ag2HgI4 are 67o C and 47-51o C respectively. The measured ranges were 65-68o C and 45-50o C. The slight deviation from expected values can be attributed to the difficulty in seeing the color change in the device that the measurements were taken in. The light of the device is a dark yellow; as the color changes were from red to brown and yellow to orange, it was hard to distinguish exactly when the color change started and stopped. Continuing on, however, the high degree of correspondence to literature values implies that the products were of high purity and that the products formed were truly Cu2HgI4 and Ag2HgI4.

        The resistance measured/observed for the Ag2HgI4 precipitate makes sense. The trend, during the final part of the experiment, was that as the heat increased, conductivity increased once thermochromatic temperature was met. Conductivity increased because resistance decreased, from overload to measurable numbers such 0.220 MW. This is possible because  at the thermochromatic temperature, disorder starts causing cations to become randomly distributed throughout the holes in the structure, thus increasing it’s conductivity for electricity.

Post Lab Questions

1. 2NaCl + CuSO4*5H2O  ------>  CuCl2+ Na2SO4 + 5H2O
     2KI + HgI2 -------> K2HgI4
    2AgNO3 + HgI42- -------> Ag2HgI4+ 2NO3-
    2CuCl2 + HgI42- --------> Cu2HgI4 + 4Cl-

2. Metal cations are responsible for ionic conductivity (in this case, silver and copper). Its expected that silver is more mobile as it is the better conductor. This is because it is a solid lattice structure, unlike mercury, making its electrons freer to move around than in mercury, which is not ordered. Mercury, unlike silver, has little electrical potential. Silver also has a charge of +1, making it less resistant to lose an electron than mercury with a charge of +2 (the state of mercury used in this experiment).

CONCLUSION

        In conclusion, the percent yields of Cu2HgI4 and Ag2HgI4 (127.07% and 141.6% respectively) were theoretically impossible, it was likely caused due to the presence of water, as the precipitates were not allowed to completely dry before their weights were taken. This also corresponds with the fact that the thermochromatic temperatures were nearly exactly the same with literature values, save for a slight deviation (possibly caused due to difficulty seeing in the light of the temperature device). The resistance observed when heating the Ag2HgI4 (decreasing as temperature increases once thermochromatic temperature is met) corresponds to what was expected. Increasing the temperature increased the electrical conductivity.

        During the experiment, an ice bath was used to increase precipitate production. It wasn’t mentioned in the actual lab and would be a nice, albeit small, addition.