6. A fluoride ISE immersed in 1 x 10-2 mol dm 3 solution of sodium fluoride gives a potential of 35,2 mV and when it is immersed in a tooth paste solution it gives a potential of 30,2 mV. What is the concentration of fluoride ion in the toothpaste? (En E) pF mk = pFa + unk std unk 0.0591