The measurement of pH using a glass electrode obeys the Nernst equation. The typical response of a pH meter at 25.00°C is given by the equation ?meas = ?ref + 0.05916 pH where ?ref contains the potential of the reference electrode and all other potentials that arise in the cell that are not related to the hydrogen ion concentration. Assume that ?ref = 0.250 V and that ?meas = 0.480 V. a. What is the uncertainty in the values of pH and [H+] if the uncertainty in the measured potential is ±1 mV (±0.001 V)? b. To what precision must the potential be measured for the uncertainty in pH to be ±0.02 pH unit?
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We are given the equation for the response of a pH meter: $E_{meas} = E_{ref} + 0.05916 \times pH$. Show more…
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The measurement of $\mathrm{pH}$ using a glass electrode obeys the Nernst equation. The typical response of a pH meter at $25.00^{\circ} \mathrm{C}$ is given by the equation $$\mathscr{E}_{\text { meas }}=\mathscr{E}_{\text { ref }}+0.05916 \mathrm{pH}$$ where $\mathscr{E}_{\text { ref }}$ contains the potential of the reference electrode and all other potentials that arise in the cell that are not related to the hydrogen ion concentration. Assume that $\mathscr{E}_{\mathrm{ref}}=0.250 \mathrm{V}$ and that $\mathscr{E}_{\text { meas }}=0.480 \mathrm{V}$ a. What is the uncertainty in the values of $\mathrm{pH}$ and $\left[\mathrm{H}^{+}\right]$ if the nncertainty in the measured potential is $+1 \mathrm{mV}$ $( \pm 0.001 \mathrm{V}) ?$ b. To what precision must the potential be measured for the uncertainty in $\mathrm{pH}$ to be $\pm 0.02 \mathrm{pH}$ unit?
The cell SCE || H⁺ (a = x) | glass electrode has a potential of 0.2106 V when the solution in the right-hand compartment is a buffer of pH 4.006. Calculate the pH and the hydrogen ion activity of each unknown, if when the buffer is replaced with unknowns, the following potentials are obtained: a -0.2883 V. pH = Hydrogen ion activity = M b +0.1195 V. pH = Hydrogen ion activity = M c Assuming an uncertainty of 0.002 V in the junction potential, what is the range of hydrogen ion activities within which the true value might be expected to lie? For part (a) M < hydrogen ion activity < M For part (b) M < hydrogen ion activity < M
Sri K.
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