pH pen to control acidity in liquid  

pH pen to control acidity in liquid
pH pen and pH meter
pH pens have a fixed electrode that cannot be replaced. The advantage is that the pH pens are convenient to use in the field.

pH meter combined instrument has removable electrode. If the electrode is poor, one does not replace the measuring unit, but only buy the new electrode. When the pH meters are clumsier to use in the field, they are used primarily for accurate measurements in the laboratory.

One and two-point calibration
One-point calibration must be calibrated using a pH 7 solution. The electrode is immersed in the solution and the meter is adjusted to pH 7.

Two-point calibration provides accurate measurements over a wider range. First it is calibrated with a pH 7 solution and then either pH 4 with a solution or a pH10 solution.

Temperature compensation
pH value changes with temperature. Therefore, more advanced pH meter opportunity for temperature compensation.

Electrode
The electrode tip is composed of small pores in the glass. During storage, it is quite normal that a little electrolyte escapes and settles like a white coating. The coating must be soaked before measurement because the pores should not be blocked.

If pH pen takes a long time to stabilize or if the readings continuously change, this is due probably to the pores of the electrode is stuck. To clean the electrode it is placed in concentrated sulphuric acid for half a minute and then the electrode is carefully rinsed with distilled water.

pH measurement in soil
For the measurement of the Earth there are special electrodes for pH meter with resolve probes. The electrode on pH meter for soil consists of two different metals. It is important that the probe metal surfaces are kept clean from coatings to the pH meter to give accurate readings.