pH Indicators

A pH indicator is a colour changing (or halochromic) chemical compound that is added in small amounts to a solution so that the pH (acidity or basicity) of the solution can be determined visually.

A pH indicator is a chemical detector for hydronium ions (H3O+) or hydrogen ions (H+).  Normally, the indicator causes the colour of the solution to change depending on the pH.

pH (potential of hydrogen) is a scale of acidity from 0 to 14. It tells how acidic or alkaline a substance is. More acidic solutions have lower pH. More alkaline solutions have higher pH. Substances which are not acidic or alkaline (neutral) usually have a pH of 7. Acids have a pH less than 7. Alkalis have a pH greater than 7.

pH indicator solutions are themselves weak acids or bases.  As one chemical is added it changes the arrangement of the electrons in the molecule causing it to absorb different wavelengths of light and therefore appear different in colour.

Different chemicals can be used for different pH ranges as shown in the diagram below.

 

pH indicators are frequently employed in titrations in analytical chemistry and biology to determine the extent of a chemical reaction. Because of the subjective choice (determination) of colour, pH indicators are susceptible to imprecise readings. For applications requiring precise measurement of pH, a pH meter is frequently used.

Many plants or plant parts contain chemicals from the naturally-coloured anthocyanin family of compounds. They are red in acidic solutions and blue in basic. Anthocyanins can be extracted with water or other solvents from a multitude of coloured plants or plant parts, including from leaves (red cabbage); flowers (geranium, poppy, or rose petals); berries (blueberries, blackcurrant); and stems (rhubarb). Extracting anthocyanins from household plants, especially red cabbage, to form a crude pH indicator is a popular introductory chemistry demonstration.

For more information visit:-

http://en.wikipedia.org/wiki/PH_indicators

http://www.compoundchem.com/2014/04/04/the-colours-chemistry-of-ph-indicators/

 

Back to school

Where did the summertime break go?  Time for kids to go back to school.  And time for us too...chemistry basics.....Acids and bases

All acids:

• have a low pH (1-6) – the lower the number the stronger the acid
• react with bases to form neutral compounds
• are corrosive when they are strong
• are an irritant when they are weak.

Acids have a pH of less than 7. Bases have a pH of more than 7. When bases are dissolved in water, they are known as alkalis. Salts are made when an acid reacts with a base, carbonate or metal. The name of the salt formed depends on the metal in the base and the acid used. For example, salts made using hydrochloric acid are called chlorides.

Acids
Substances with a pH of less than 7 are acids. The more strongly acidic the solution, the lower its pH number. Acidic solutions turn blue litmus paper red. They turn universal indicator paper red if they are strongly acidic, and orange or yellow if they are weakly acidic.

Bases
Substances that can react with acids and neutralise them to make a salt and water are called bases. They are usually metal oxides or metal hydroxides. For example, copper oxide and sodium hydroxide are bases.

Alkalis
Bases that dissolve in water are called alkalis. Copper oxide is not an alkali because it does not dissolve in water. Sodium hydroxide is an alkali because it does dissolve in water.

Alkaline solutions have a pH of more than 7. The stronger the alkali, the higher the pH number. Alkalis turn red litmus paper blue. They turn universal indicator paper dark blue or purple if they are strongly alkaline, and blue-green if they are weakly alkaline.

Neutral solutions
Neutral solutions have a pH of 7. They do not change the colour of litmus paper, but they turn universal indicator paper green. Water is neutral.

For pH meters or pH test papers or buffer solutions give us a call.

For more information visit:-
http://www.prlabs.co.uk
http://en.wikipedia.org/wiki/PH