Difference between pH Meter and pH Test Paper
In pH measurement, there are cases where the value measured by the pH test paper of the same solution differs greatly from the value measured by the industrial pH meter, even a few pH units! Which do we believe? what’s the difference?
Differences between pH meters and pH test strips on different testing principles:
- In fact, the pH meter with glass electrode has been a technology N years ago, and it is very mature now, but PH test strips are used and known by more people as a convenient and easy test method.
- Industrial pH meter: glass electrodes are generally used, and the relationship between the membrane potential Em and the hydrogen ion activity (H+) of the solution to be measured conforms to the Taiwan Nernst equation:
- E = Eo + 2.3 RT/F • lg aH+
Therefore, the pH meter does not need to consume H+ or OH- when measuring pH. Therefore, the value measured by the pH meter more accurately reflects the actual pH of the solution!
pH test paper:
For all kinds, like pH health test strips the principle is based on the color reaction of the indicator. Test strips contain a certain amount of indicators. When it changes from one color to another, it consumes a certain amount of H+ or OH-. When there is not enough H+ or OH in the solution to change the indicator from one color to another, pH paper cannot accurately show the pH of a solution.
Differences between pH meters and pH test strips in different applications:
What does ph paper test for:
- The full range ph 1-14 test paper strips will consume a certain amount of H+ or OH- during the test, so the ph test paper strips are prone to errors!
- For strong acid solutions and strong alkali solutions, ph test strips generally do not produce errors.
- The ph test strips can better reflect the properties of the buffer solution: within the buffer range of the buffer system, the full range ph 1-14 test paper strips can well display the actual pH value of the solution; when it exceeds the buffer range, the ph test strips value will deviate from the pH value of the solution. Severe to several pH units
What do ph meters test for:
- In our daily life, we often see pH meters. In fact, different occasions require different pH meters. The choice of each enterprise should be selected according to the actual situation and practical point of view. Test paper widely used in the general chemical industry is an inaccurate pH measurement method. If accuracy is required, a pH meter must be used.
- Wide bars are judged by contrasting colors. This test method is not recommended for darker-colored products. Deionized water (without any substances) was conditioned with dilute sulfuric acid and sodium hydroxide in the experiments. When adjusted to 8, use pH paper to test 6, but the buffer is measured to 9.18 with pH paper, the color is correct, use a pH meter. 9.18 The buffer solvent is also correct.