The influence of various forms of carbon dioxide in water on its pH value | tiwater.info

The influence of various forms of carbon dioxide in water on its pH value | tiwater.info

I present to your attention the article that shows how the pH value depends on various forms of carbon dioxide dissolved in water. This article is a part of the method for controlling the water-chemical mode of low-pressure steam boilers. The article contains theoretical justification which helps to exercise simple control of the water-chemical mode, which does not require the use of chemical analyses during the operation of the boiler room. The description of the technological process of the control of the water-chemical mode with an example will be presented soon in the next article (Ivan Tikhonov “The monitoring of the water-chemical mode of low-pressure steam boilers using the pH value of boiler water”).

Annotation

This article discusses the existence of various forms of carbon dioxide in water. The importance of measuring the pH value in determining the ratios of bicarbonates, carbonates and hydrates is shown. The article presents a method for calculating the pH value of water depending on the ratio of various forms of carbon dioxide in water. The developed method is adapted for calculating the pH value of water in the alkaline range. The article presents the results of calculations using this method and it compares the calculated and experimental data.

It is known that carbon dioxide is found in water in a bound, semi-bound and free form. The bound form includes carbonate ions (CO32-), semi – bound bicarbonate ions (HCO3-), and free form carbonic acid dissolved (H2CO3) and gaseous (CO2).

The total amount of carbon dioxide in water is defined as the sum of all three forms.

ƩСО2 =СО2 + Н2СО3 + НСО3- + СО32- (1)

 

The amount (concentration of carbon dioxide forms) is measured in mmol / l. These forms of carbon dioxide are in a certain balance. The percentage of concentrations of various forms of carbon dioxide depends on the pH value of water. Thus, when the pH value of water is 8.37, there is practically no free form of carbon dioxide in the water and, accordingly, only bicarbonate ion exists and a carbonate ion begins to appear (Fig. 1).

 

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