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.
