Fig 1.
A photo of the electrochemical cell.
Fig 2.
Potential difference between solutions produced by a water electrolyzer.
Solutions in the right beaker (connected to the negative terminal of the voltmeter, Fig 1) were kept at pH 7, while solutions with pH 2, 6, 9, or 10 were placed in the left beaker. The pHleft−pHright indicates the pH value of the solution in the left beaker minus the pH value of the solution in the right beaker. For example, when the pH of the solution in the left beaker was 9, the pHleft−pHright value would be 2 (i.e., 9 minus 7).
Fig 3.
Potential difference between acids and bases.
Solutions of various pH values were prepared by adding varied amounts of DI water to concentrated HCl or 1 M NaOH. For the experiments at reference value of pH 4, solutions of pH 4 in one beaker (right in Fig 1) were connected to the negative terminal of the voltmeter, while solutions with various pH values (i.e., 2, 4, 7, 10, 12, and 14) were added to the left beaker, which was in turn connected to the positive terminal of the voltmeter. Similarly, for experiments at pH 10, the solutions in the right beaker were maintained at pH 10. The pHleft−pHright indicates the pH value of the solution in the left beaker minus the pH value of the solution in the right beaker. For example, when the pH of the solution in the left beaker was 12, and the pH of the solution in the right beaker was 10, the pHleft−pHright was 12 minus 10, or 2.
Table 1.
(a) Electrical potential differences between acids (HCl) with differing pH values and neutral solutions (containing 1μM NaCl); and, bases (NaOH) and neutral solutions (containing 1μM NaCl).
Measurements taken at different times to test stabilitya. (b) Electrical potential differences between acids (HNO3) and neutral solutions (containing 1 μM NaCl); and, bases (KOH) and neutral solutions (containing 1 μM NaCl)a.
Table 2.
Platinum electrodes replacing stainless steel electrodes.
(a) Electrical potentials between acids (HCl) and neutral solutions (containing 1μM NaCl), and bases (NaOH) and neutral solutions (containing 1μM NaCl)a. (b) Electrical potentials between acids (HNO3) and neutral solutions (containing 1μM NaCl), and bases (KOH) and neutral solutions (containing 1μM NaCl)a.
Fig 4.
Potential differences between common salt solutions and DI water (containing 1 μM NaCl).
(a) NaCl solutions of different concentration in one beaker (left in Fig 1) were connected to the positive terminal of the voltmeter, while neutral solutions were contained in the other beaker (right in Fig 1), which was connected to the voltmeter’s negative terminal. (b) Experiments with KCl were arranged similarly. Stainless steel wires were used as electrodes.
Fig 5.
Similar to Fig 4, but with different salts.
Stainless steel wires were used as the electrodes.