There is an error in the measurement of the pH meter and the pH test paper when measuring the pH value in the experiment
There are errors in the measurement of the pH meter and the pH test paper when measuring the pH value in the experiment. This article focuses on the measurement error of the pH acidity meter and the pH test paper during the experiment. In the experiment, dilute sulfuric acid and sodium hydroxide were used to adjust the deionized water (which does not contain any substances), and when it was adjusted to 8, it was measured as 6 with PH test paper, but the buffer solution was measured at 9.18 with PH test paper, and the color was correct. 9.18 The buffer solvent is also correct. What’s going on here, it’s just that many people may not use the pH meter and the pH test paper to measure the pH below 3 and above 8. The test paper must have no problem.
1. Problems in the actual operation of the pH meter: Enthusiastic netizens have mentioned that the technicians and production personnel in some units feel that the pH meter is not easy to use, troublesome to use, and the data is inaccurate. Since we use it frequently, the pH standard solution has a short validity period. People in the unit are accustomed to using single-color pH test paper, which is more accurate than pH meter and easy to control in actual operation. There are also three-color test papers, but they are poorly made. I have used foreign five-color pH test papers, and the solution is well dispersed on them, and the color development is also very clear.
Some netizens also mentioned that the pH meter is not accurate, and the pH test paper is also inaccurate. Let's see what it sounds like below.
2. Answers to the above questions. Enthusiastic netizens mentioned that the pH test paper measured the buffer solution as 9.18. I think there is a problem with this statement. It is impossible to measure the PH test paper to two decimal places, and the accuracy is not so high. It is just a rough measurement. If you want an accurate pH during the experiment, then I think it is better to use a PH acidity meter. As for why it is inaccurate when adjusting deionized water, but accurate when measuring buffer solution, there are many reasons;
1. There may be no uniform mixing;
2. There may be a problem with the test strip. Wait. This netizen thinks this is not the main problem. In short, in a word, if the value is to be accurate, it is better to use a pH meter to measure it.
3. System answers given by enthusiastic netizens
First of all, the deionized water itself should be measured with a conductivity meter to see if the resistance reaches 18MOhm and the conductance is lower than 0.1 microSiemens.cm-1. If not, your "deionized water" itself is the problem.
First, using dilute sulfuric acid and NaOH to adjust the pH value is quite a layman's action, which is not like the experimental operation of an undergraduate who has received formal chemical experiment training. If the goal is to adjust the pH value, a buffer solution is required. How can dilute sulfuric acid and NaOH obtain a solution with a relatively stable pH value. Don't forget the carbon dioxide in the air, the pH of the solution made with these two things changes.
Third, pH test paper, I have seen some with a pH of 0.1, but I have never seen one with a pH of 0.01. Please pay attention to your own expressions. If there is a pH meter, at least two points of calibration are required before any measurement is made. I believe it is very possible to ignore this crucial step. If the slope is lower than 90% after calibration, the pH meter data is not reliable enough. If these terms have never been heard before, please read the instructions for use before using the pH meter, and if possible, take a good look at the instrument analysis textbook.
Fourth, why use relatively inaccurate pH test paper when there is a pH meter, these two cannot be mutually verified. I have never seen a person who studies analytics do this.
4. Diligent calibration is the key to ensure the accuracy of the pH meter
A calibrated pH meter is definitely better than a pH test paper. Diligent calibration is required to maintain accuracy.
The widely used test papers in the general chemical industry are all non-accurate determinations of the pH value. If accuracy is required, a pH meter must be used. Extensive test paper is judged by comparing colors. For products with darker colors, this test method is not advisable.
