WATER IN A GLASS WHY DOES THE PH VALUE RISE

It should be the alkali metal ions in the glass – mainly Na+ that are free into the water, but it shouldn't be so severe.

In the glass industry, there is a condition called glass mold - the whole piece of glass that has been drenched in rain will turn white and moldy over time, and finally stick to each other. The mechanism is that the H+ in the water replaces the Na+ in the glass, so that the pH value of the water rises to become an alkali solution, and further forms the reaction between the alkali and the silicon in the glass (the glass is afraid of alkali, so the laboratory caustic soda bottle can not use a grinding bottle).

It has been reported that the final pH value of rainwater between the glasses can reach above.

You try to compare the water in a plastic cup to see if it's caused by the glass.

The groundwater pressure is high, and in contact with the rock, it will dissolve more carbonic acid, and after pumping, the pressure is small, and the carbonic acid overflows, but the alkaline mineral salts are still there, and the pH is only large.

When influencing factors such as carbon dioxide absorption, agitation of the solution, temperature, voltage, 、...... without considering the environmentIt should be the following reasons:

1. Due to the very low ion concentration in pure water, the concentration difference between the high concentration of KCl in the salt bridge solution of the reference electrode is large, and it is very different from the situation in ordinary solution. Pure water increases the permeation rate of the salt bridge solution, promotes the loss of the salt bridge, and thus accelerates the decrease of the concentration of K+ and Cl-. This causes a change and instability of the junction potential, while the potential of the AGCl reference electrode itself depends on the concentration of Cl-.

As the Cl- concentration changes, so does the potential of the reference electrode itself. Drift of measured values occurs.

2. In order to ensure the pH zero potential of the composite electrode, the salt bridge must use a high concentration of KCl, and at the same time, in order to prevent the AG AGCL coating from being dissolved by a high concentration of KCL, powdered AGCL must be added to the salt bridge to make the salt bridge solution saturated with AGCL. However, due to the decrease of the concentration of KCl in the salt bridge solution, AGCL is supersaturated and precipitates, which blocks the liquid junction.

3. Because the internal resistance of the glass resistance is very high, the higher the internal resistance, the thicker the glass film, the asymmetric potential will increase, the inertness of the electrode will also increase, and the generation of electromotive force will be slower. Pure water has no buffering effect, and unlike standard buffer solutions, the electrode potential build-up time will be slow.

In addition to the instability of the measured values, they are not accurate. Because the conductivity of pure water is very low, the friction between the water flow and the electrode surface is similar to the friction between insulators, which can produce electrostatic charges, and due to the action of electrostatic charges, an ER that is not related to the pH value of the measured water sample is generated in the measurement battery, and the ER is superimposed on the measurement signal, which will cause the pH measurement error.

If it is necessary to measure, it is recommended to use a solid contact glass electrode, increase the sample volume, adjust the total ionic strength with reference to GB, and increase the conductivity.

To be honest, I didn't understand the above words.

Copy-pasted.

The metal in the stainless steel cup will have a little trace of ionization.

Whereas, metal ions are all positively charged.

So some of the hydroxide ions in the water will be neutralized.

This gives you a little more hydrogen ions.

The more hydrogen ions, the lower the pH.

The cleanliness of your glass and stainless steel cups and measurement errors can lead to this.

Because the main component of glass is SO2 stainless steel, as long as the composition is FE, FE is more acidic.

Because both also have a pH ......