The substrate processing step involves the use of HF, which is again controlled

Question

The substrate processing step involves the use of HF, which is again controlled in the allowed concentration in the effluent. The concentration of HF in the effluent is measured using a fluoride ISE, and the method of standard additions is employed. Here, the method is to take a sample of the effluent water, add to it a volume of ISAB and take a reading, then add a volume of a fluoride standard and take a second reading. If your electrode has a sensitivity of -60.0 mV/decade, the potential measured in the sample (after ISAB addition) is +155 mV, the potential after the standard addition is 53.6 mV, the volume of unknown is 100 mL, the volume of ISAB is 10 mL, the volume of standard is 1 mL and the concentration of the standard is 10,000 ppm (ten thousand parts per million) what is the concentration of F- in the sample?

2.1 ppm

1.3 ppm

3.2 ppm

4.9 ppm

Explanation / Answer

Given the substrate processing step involves the use of HF, which is again controlled in the allowed concentration in the effluent. The concentration of HF in the effluent is measured using a fluoride ISE, and the method of standard additions is employed. Here, the method is to take a sample of the effluent water, add to it a volume of ISAB and take a reading, then add a volume of a fluoride standard and take a second reading. If your electrode has a sensitivity of -60.0 mV/decade, the potential measured in the sample (after ISAB addition) is +155 mV, the potential after the standard addition is 53.6 mV, the volume of unknown is 100 mL, the volume of ISAB is 10 mL, the volume of standard is 1 mL and the concentration of the standard is 10,000 ppm (ten thousand parts per million)

The concentration of F- in the sample = 2* 10000* 1 (60-53.6) = 3.2 ppm.

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