“…if the blue litmus paper turns red in the solution, then it’s an acid (I guess); if the red litmus paper turns blue, then the solution is basic.” Well, you probably remember meeting such a phrase before if you ever attended a Chemistry class. The science behind taking pH measurements back then was also pretty simple. You could just dip that litmus paper in some unknown solution and thereafter you could check out the color change of the litmus paper in some pH chart to determine the pH of a given solution, do you remember doing that too? That was pretty simple and straightforward, wasn’t it?
However, there obviously exist huge chances of making faults with that good old method. The main drawback to them (in my opinion) being the ability to distinguishing the colors. Boy, color-blind people of my brand cannot distinctly distinguish pink from purple; so how then can we know which red is redder than the other or which blue is lesser blue than the other? Yet, it should be important to note that if you made mistakes in reading pH in real-life, this mistake could be very costly as it could cost your entire project. That is why in practical applications, some people do invest in using pH meters that measure the pH directly.
How does a pH Meter work? –principle behind the workings of a pH meter
Perhaps before I could answer this, kindly allow me to take you back to class and define the main difference between an acid and a base. My Chemistry teacher taught me that the difference between an acid and a base is that:
An acid is a proton donor. Acids dissolve in water to form positively charged Hydrogen ions (H+) while a base is a proton acceptor. Bases dissolve in water to form negatively charged hydroxonium ions (OH–).
Bearing that in mind, then it could be clear that acidic solutions do contain more protons (positively charged ions) than basic solutions. This means acidic solutions have a higher ability (potential) to generate an electric current than a basic solution under different solutions.
The pH meter utilizes this knowledge in determining the pH of an unknown solution. The science behind a pH meter borrows much from that of a voltmeter. Given the solution of an unknown pH, it first measures its voltage then it compares it with the voltage from an already known solution. The difference between the two (Potential Difference) gives us the difference in the pH of the solutions.
What is a pH meter composed of?
Well, the answer to this could greatly vary as nowadays there exist several pH meters on the market made from different compositions. However, since the principle of operation is the same, the difference doesn’t seem too big. A normal pH meter, for instance, has got the following:
- The pH meter itself (often a moving coil meter) that has an attached analog pointer that moves on a scale. Some advanced ones do come with a digital scale.
- Electrodes: these are the ends that you connect into a solution to enable you to take a reading.