## Mathematics in taste buds !!!

Sweet and sour:

Chemists frequently need to describe how acidic or alkaline a particular solution is: that is, to give a quantitative measure of its concentration of hydrogen ions, $H^{+}$. The scale generally used is the pH scale; pH means potential for hydrogen.

The pH ranges from 0 to 14; a pH below 7 indicates that the solution is acidic, and a pH greater than 7 indicates that the solution is alkaline. A neutral solution such as pure water has a pH of 7. (Strictly speaking, the temperature must be mentioned when we quote the pH value. For pure water, pH equals 7 only at 25 deg celsius.) Full strength sulphuric acid $H_{2}SO_{4}$ has a pH of 0, as does concentrated nitric acid ($HNO_{3}$), or concentrated hydrochloric acid (HCl).

The pH scale was invented in 1909, by a Dutch biochemist, Soren Sorenson. The scale is logarithmic in nature; pH is defined by the equation

$pH = - \log_{10}{H^{+}}$

where $H^{+}$ refers to the concentration of $H^{+}$ ions, expressed in moles per liter. A solution with a pH of 4 contains $10^{-4}$ moles of $H^{+}$ ions per liter, and so on.

The pH may be  measured by using an electronic pH meter, or by means of special dyes called acid-base indicators. The dyes respond to the acidity level by changing colour in a way that depends on the pH. Another measuring device is pH paper. This has indicators within it, which change colour at different pHs.  When dipped into a solution, the paper colour indicates the approximate pH of the solution.

Many chemical reactions depend on pH, indeed, they may be highly sensitive to pH. Agricultural practices have to take soil pH into consideration, because certain crops grow best in an acidic soil ($pH < 7$) whereas others grew best in an alkaline soil $pH > 7$. When the soil is found too acidic, lime may be added to make it more alkaline (“sweeten it” to use the gardener’s terminology). The fallen leaves of certain trees contribute to the soil’s acidity and the consequent lack of growth of plants in the shade of the tree. This happens, for example, with eucalyptus trees.

More later, can u find more such examples and share with us?

Nalin Pithwa

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