PH OF SUBSTANCES, COMPOUNDS, MIXTURES
pH is a scale from 0 to 14 for measuring acidity or alkanity. It tells how acidic or alkaline a substance is. The lower the pH, the more acidic is the solution. The higher the pH, the more alkaline is the solution. A pH of 7 indicates neutrality – substance which is not acidic or alkaline is called neutral. Acids have a pH less than 7. Alkalis have a pH greater than 7.
pH is a measure of the concentration of protons (H+) in a solution. S.P.L. Sørensen introduced this concept in 1909. The p stands for the German potenz, meaning power or concentration, and the H for the hydrogen ion (H+).
The formula for calculating pH is:
The pH value of a solution equals the negative logarithm of the concentration of hydrogen ions.
Strong acids, such as those used in car batteries, have a pH of about 2; strong alkalis such as sodium hydroxide have a pH of about 13. Acidic fruits such as citrus fruits are about pH 4. Fertile soils have a pH of about 6.5 to 7, while weak alkalis such as soap have a pH of about 9 to 10.
Indicators
Some organic substances are changing composition of double bonds in molecule in dependence of pH, what is registered by colour change. For example tea changes its colour when lemon juice is added. We call this substances indicators. We can measure acidity by adding indicator into solution and by comparing colour with colour scale.
Colour changes of indicators are the most often used for determining titration, which is for determining of volume of acid or hydroxide in analysed sample.
For approximate orientation about acidity of measured solution, we use litmus paper, what is piece of paper filled with litmus. For more exact information about acidity of measured solution, we use universal indicator paper. Its colour is changing with pH of measured solution from red to dark blue.
Examples of values of pH in common life:
Blood – pH of blood is 7,4. If this value is lower than 7,37 we are talking about acidosis. Potatoes = 6,1; Carrot = 5; Sugar = 5 - 6; Chocolate = 7,2 - 7,6; Strawberries = 3 - 3,5; Crab = 7; Lemon = 1,8 - 2; Bananas = 4,5 - 5,2; Cucumber = 5,1 - 5,7.
pH Balanced Cosmetic Products
7 is the neutral spot for pH but anything between 6.5 to 7.5 is considered to be a neutral range. A pH balance skin care product is one that is adjusted to have the same pH as the hair or skin. This is an attempt to keep someone from using a product that is too-alkaline. The real fact is that most of the time the pH of the product does not effect how irritating it will be to the skin.
Most good natural skin cleanser, moisturizers and hair conditioners have a pH level between 3.5 and 5.5 which is close the pH level of the skin or hair. While most natural shampoos have a pH level over eight, which is much more alkaline then that of the skin or hair.
The fact that a product has been adjusted to be pH balanced can dry out the skin because of the substances that have been added to the product to balance the product.
To make a shampoo pH balanced manufacturers often put chemical acid called triethanolamine (TEA), which may be contaminated with nitrosamines that have been known to cause cancer.
Example: Dove - Dove is primarily made from synthetic surfactants, as well as some vegetable oil based soap ingredients, such as sodium palm kernelate. Dove is formulated to be pH neutral, with a pH that is usually between 6,5 and 7,5.
Importance of soil pH
The pH of soil or more precisely the pH of the soil solution is very important because soil solution carries in it nutrients such as Nitrogen (N), Potassium (K), and Phosphorus (P) that plants need in specific amounts to grow, thrive, and fight off diseases.
If the pH of the soil solution is increased above 5,5, Nitrogen (in the form of nitrate) is made available to plants. Phosphorus, on the other hand, is available to plants when soil pH is between 6 and 7.
Søren Peder Lauritz Sørensen
9 January 1868 - 12 February 1939
Danish chemist, famous for the introduction of the concept of pH, a scale for measuring acidity and basicity. He was born in Havrebjerg, Denmark.
From 1901 to 1938 he was head of the prestigious Carlsberg Laboratory, Copenhagen. While working at the Carlsberg Laboratory he studied the effect of ion concentration on proteins, and because the concentration of hydrogen ions was particularly important, he introduced the pH-scale as a simple way of expressing it in 1909. The article in which he introduced the scale (using the notation pH), described two new methods for measuring acidity. The first method was based on electrodes, while the second included comparing the colours of samples and a preselected set of indicators.
He is also known for the Sørensen formol titration.
pH Tests
The pH plays a highly important role in biochemistry, chemistry and technology since it affects numerous chemical processes. The results of many analytical methods are influenced by the pH of the solvent or buffer. The measurement can be made with a pH meter or with rapid tests, such as pH indicator paper or strips and pH indicator solutions (pH indicator mixtures). The great advantage of Merck’s rapid tests is that this method of determination can be used directly on the spot without requiring any additional help or sample preparation. The high accuracy of the results enables you to take any necessary counter-measures immediately, no matter whether in environmental analysis or the industrial sector as part of in-process controls
There are a lot of ways for finding the pH of some substance. One way is to use litmus paper. The pH paper is able to tell how strong the chemical is, whether it is a stronger acid or a stronger base.
Litmus paper
Litmus is a water-soluble mixture of different dyes extracted from lichens, especially Roccella tinctoria. It is often absorbed into filter paper. The resulting piece of paper or solution with water becomes a pH indicator (one of the oldest), used to test materials for acidity. Blue litmus paper turns red under acidic conditions and red litmus paper turns blue under basic (i.e. alkaline) conditions. Neutral litmus paper is purple. The mixture contains 10 to 15 different dyes. Litmus was used for the first time about 1300 AD by Spanish alchemist Arnaldus de Villa Nova. From the 16th century on, the blue dye was extracted from some lichens, especially in the Netherlands. The main use is to test whether the solution is acidic or alkaline. Wet litmus paper can also be used to test water-soluble gases; the gas dissolves in the water and the resulting solution colours the litmus paper. For example, ammonia gas, which is alkaline, colours the litmus paper blue. Other reactions can cause a colour-change to litmus paper; for example, chlorine gas turns blue litmus paper white – the litmus paper is bleached. This reaction is irreversible and therefore here the litmus is not acting as an indicator.
