A fluoride electrode is used to determine fluoride in a water sample. Standards and samples are dilu
ted 1:10 with TISAB solution. For a 1.00×10-3mol/L(before dilution)standard.the potential reading relative to the SCE is -211.3mV, and for a 4.00×10-3mol/L standard, it is -238.6mV. The reading with the unknown is -226.5 mV. What isthe concentration of fluoride in the sample?