Calibration data for a bromide ion-selective electrode (ISE) was collected and r

Question

Calibration data for a bromide ion-selective electrode (ISE) was collected and recorded below. The potential of the ISE was measured against a saturated calomel electrode (SCE). All solutions were buffered at a pH of 7.56. A linear calibration curve can be constructed from this data as a plot of potential (in mV) vs. pBr. Determine the slope and y-intercept of such a plot of the calibration data given. Two unknown solutions were tested for [Br-] using the same bromide ISE. The potential reading for unknown 1 was -20.4 mV and the potential reading for unknown 2 was 129.9 mV. Using the calibration curve you constructed above, determine the concentration of Br- in each unknown solution.

Explanation / Answer

calibration curve follows,E=m log[br-]+b, so after construction of a graph elecctrode potential(E) vs pBr,

Slope, m=-60mV and intercept,b=-58mV.

unknown1) m=-60mV,b=-58mV and E=-20.4

substitute the values in above eqn, we get unknown1[Br-]=0.474M

unknown 2) m=-60mV,b=-58mv and e=129.9mV

unknown 2[Br-]=0.38774M

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