pH and its testing

The correct ink balance largely depends on the correct testing of pH and conductivity. Printed in the UK investigates the best way to test correctly. Understanding the chemical composition of the fountain solution on an offset press may provide an intuitive tool to achieve good print results. It is not difficult to understand what pH is, how the pH is calculated and how it differs from the conductivity is worth having, although such knowledge is rarely used. Understanding how pH is defined can be daunting. It is defined by the hydrogen ion concentration antilog. The abbreviation for pH is the original meaning of puissance d'hydrogene, which is French, meaning the potential of hydrogen. Ions are electrons that usually rotate around the central nucleus, but are free to drift and exchange with the nucleus in an effort to maintain stability. The pH is a measure of these electrons. By measuring these ions, we were able to find the pH of the liquid. This knowledge is important for getting the right ink balance and maintaining it. We set the pH at 7 to be neutral. Above 7 is alkaline and the highest value is 14. Below 7 for acidity, the minimum value is 1. Neutral water has a pH of 7, which means that there are 10 7 gram hydrogen ions per liter of water. You must use logarithms to produce smaller, concise numbers that are easy to accept. The increase or decrease in the number of grams of hydrogen ions in the water is expressed as a power of 10 instead of a number, otherwise the number is too large. It is easier to remember this number simply by talking about the number of powers. The pH meter measures the chemical concentration of the fountain solution on the press. Drug-coated test strips that can change color are only useful guides, but there are too many variations that can affect the accuracy of test strip testing, and cannot be used as rigorous testing methods. When the pH meter's test electrode is immersed in the fountain solution, its pH is shown numerically on the LCD screen. Although pH meters are easy to use, they need to be calibrated frequently to maintain their correct function. The pH meter has a glass tube outside the electrode. When it is immersed in fountain solution, the ionic charge in the fountain solution induces electrodes in the glass tube. If the electrode is in direct contact with the solution, electrons in the solution are introduced into the electrode. In this case, the pH meter cannot indicate the correct pH. For this reason, the electrodes are sealed in a pH meter. The charge induced in the electrode generates a small current in the circuit in the pH meter. This current is amplified and digitized and then compared with the value already stored in the electronic memory in the pH meter to determine its value. The final result is displayed on the LCD panel. pH meter The test head is immersed in a solution of known concentration for correction, and then the reading is adjusted to display the desired value. The standard solution (buffer) was prepared by dissolving buffer tablets in distilled water. Buffer tablets have different values. The commonly used buffer tablets have pH values ​​of 4, 7, 9.2 and 10. When verifying with these buffer tablets, we can check the entire value area. This is called slope correction because it is checked whether the slope of the correlation curve is consistent with reality. The logic circuit in the pH meter detects the current of the probe through the pH meter and determines the current value as the corresponding setting value of the meter at that point. This will ensure that the pH meter can display this set point value each time it reads this current value. Then use the interpolation algorithm to calculate the other values ​​between the two set points. For example, if we want to check a buffer with a pH of 4, the displayed value is shown as 4.2. In this case, when we press the check button, the meter makes an adjustment so that it interprets this value as 4 instead of 4.2. However, in many cases, it is best not to check if the buffer used does not match the check value given by the pH meter. For example, the set points are 4, 7 and 10 in some pH meters. If you use the buffer values ​​4, 7, and 9.2 to verify the pH meter, an error occurs at the last control point (10 here). However, if the fountain solution used is usually acidic, its value is close to 4.5 to 5.5, so it does not affect the reading when we measure the fountain solution. Electrical conductivity is sometimes quite different. It is defined as the ability of the conductive electrons in the solution to pass through, and actually measures the amount of dissolved salt in the solution. Since the amount that can be electrically conductive in solution is directly proportional to the amount of ionic salt in solution, it can be measured as such. The conductivity can be raised without any special change in pH, and if this happens, it can be inferred that the concentration of the ionic salt has increased. Imagine if the local water supply department suddenly added some aluminum chloride to tap water for the purpose of water purification, the salt concentration in the bucket will change. This will greatly affect the surface tension of the water, leading to the destruction of the ink balance, but it may not change the pH. The conductivity meter function is the same as the pH meter, but the electrode is in direct contact with the solution, at which point the resistance of the current through the fountain solution is the defined value. Therefore, the direct current passes through the solution through both electrodes instead of through the insulated bulb. It is clear that due to the presence of buffer in the fountain solution, the pH will remain constant, although it may vary in the conductivity value. As mentioned above, this will tell us the amount of dissolved salt that appears in the solution. In other words, it states the number of positive and negative ion pairs. Since positive and negative ion pairs neutralize each other, this does not affect the detection of hydrogen ion concentration.