What is the slope of a pH meter?
The pH meter slope is used by the pH meter to convert the millivolt signal of the electrode into a pH value. It is obtained by dividing the voltage difference measured with different buffers by the buffer pl difference. The slope in the pH meter is calculated based on the Nernst equation. Generally, the slope does not appear until the balance is calibrated. The slope is a criterion for determining whether the electrode life has been exhausted.
Need indicators. Generally, there are three levels of electrode life. After calibration, the slope of the new electrode is between 95% and 105%. If the slope is lower than 90, it is recommended to replace the electrode, otherwise it will affect its measurement accuracy. pH calibration solution for pH meter calibration. The calculation of the slope is related to the electrode measuring the potential of the solution you prepare. There are three standard buffers. When calibrating, usually two are enough. If all three are involved in the calibration, the slopes will be different accordingly.
pH meter refers to an instrument used to measure the pH value of a solution. The pH meter works based on the principle of a primary battery. The electromotive force between the two electrodes of the primary battery is based on Nernst's law, which is related to both the properties of the electrodes and the concentration of hydrogen ions in the solution. There is a corresponding relationship between the electromotive force of the primary battery and the hydrogen ion concentration. The negative logarithm of the hydrogen ion concentration is the pH value. pH meter is a common analytical instrument widely used in agriculture, environmental protection, industry and other fields. Soil pH is one of the most important basic properties of soil. Factors such as the temperature and ionic strength of the solution to be measured should be considered during the pH measurement process.
What is pH? pH is the abbreviation of the Latin word "Pondus hydrogenii" (Pondus=pressure, pressure hydrogenium=hydrogen) and is used to measure the activity of hydrogen ions in a substance. This activity is directly related to the acidity, neutrality and alkalinity of the aqueous solution. Water is chemically neutral, but it is not without ions. Even chemically pure water is dissociated in trace amounts: strictly speaking, hydrogen nuclei do not exist in a free state before hydrating with water molecules.
H2O+ H2O=H3O++ OHˉ. Since the concentration of hydronium ions (H3O+) is treated the same as the concentration of hydrogen ions (H+), the above formula can be simplified into the following commonly used form: H2O=H++ OHˉ
The positive hydrogen ions here are expressed as "H+ ions" or "hydrogen nuclei" in chemistry. Hydronium nuclei are represented as "hydronium ions". Negative hydroxide ions are called "hydroxide ions".
Using the law of mass action, an equilibrium constant can be found to express the dissociation of pure water:
K=H3O+×OH-----H2O
Since only a very small amount of water is dissociated, the molar concentration of water is actually a constant, and there is an equilibrium constant K that can be used to calculate the ion product KW of water.
KW=K×H2O KW= H3O+·OH－=10－7·10－7=10－14mol/l (25℃)
That is to say, for one liter of pure water at 25°C, there are 10-7 moles of H3O+ ions and 10-7 moles of OHˉ ions.
In neutral solution, the concentrations of hydrogen ions H+ and hydroxide ions OHˉ are both 10-7mol/l. like:
If there are excess hydrogen ions H+, the solution is acidic. Acid is a substance that can dissociate hydrogen ions H+ in an aqueous solution. Likewise, if the OHˉ ion is freed, the solution is alkaline. Therefore, giving the H+ value is enough to indicate the characteristics of the solution, whether it is acidic or alkaline. In order to avoid using the negative power exponent of this molecular concentration to calculate, biologist Soernsen suggested in 1909 that this inconvenient value should be used. Values are replaced by logarithms and defined as "pH value". Mathematically, pH is defined as the negative logarithm of the hydrogen ion concentration. That is pH=-log[H+].
