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pH Meter
pH
pH is a unit of measure which describes the degree of acidity or alkalinity (basic) of a solution.
It is measured on a scale of 0 to 14.
It is defined as the negative logarithm of the hydrogen ion concentration.
pH = -log[H+]
The pH scale is logarithmic, so a one unit change in pH actually reflects a ten fold change in the acidity or alkalanity.
pH value
The pH value of a substance is directly related to the ratio of the hydrogen ion and hydroxyl ion concentrations.
If the H+ concentration is higher than OH- the material is acidic.
If the OH- concentration is higher than H+ the material is basic.
7 is neutral, <7 is acidic, >7 is basic
pH Measurement
A pH measurement system consists of three parts: a pH measuring electrode, a reference electrode, and a high input impedance meter.
The pH measuring electrode is a hydrogen ion sensitive glass bulb.
The reference electrode output does not vary with the activity of the hydrogen ion.
The reference electrode supplies a constant value against which we measure the potential of the pH electrode
pH Meter
A sample is placed in a cup and the glass probe at the end of the retractable arm is placed in it.
The probe is connected to the main box.
There are two electrodes inside the probe that measure voltage.
One is contained in liquid with fixed pH.
The other measures the acidity of the sample through the amount of H+ ions.
Digital pH meter