An unknown metal is believed to be either Sn or Cd
CHEMISTRY · Multi-part · AP · Chemistry · Thermodynamics and Electrochemistry · Thermodynamics and Electrochemistry
Problem
An unknown metal is believed to be either Sn or Cd, each existing in aqueous solution only as the 2+ ion. To identify the metal, a student performs three separate electrolysis trials, each using the same electrolyte but different electrical conditions. The experimental data are summarized in the table below.
Trial
Current (A)
Time (min)
Mass of metal deposited (g)
1
2.10
25.0
1.83
2
1.75
40.0
2.44
3
3.00
18.0
1.88
Assume the Faraday constant is 96 485 C mol−1 of electrons.
(a) For each trial, calculate the molar mass obtained from the experimental data.
(b) Compute the average of the three experimental molar-mass values.
(c) The accepted molar masses are 118.7 g mol−1 for Sn and 112.4 g mol−1 for Cd. For each candidate metal, determine the percent error relative to the average experimental value from part (b).
(d) Using your calculations, identify the unknown metal and provide a quantitative justification that includes both the percent-error analysis and the consistency of the three trials.