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Acids, Bases and Neutral Substances

Compounds are substances that are made up of two or more combined elements. There are three types of compounds; acids, bases and salts.
 
Acids and bases are everywhere. They are used in everyday life, from the food we eat to the soap we use. Nearly every substance you see and use are acids or bases, except for pure water and salts. They are neither an acid nor a base, instead they are neutral.

What is an Acid?
 
An acid is a substance that forms hydrogen (H+) ions in a solution. In other words acids are compounds which break into H+ ions and another compound when placed in a solution (one which is mainly water).
 
Acids can be found in many substances, including food. Fruits contain an acid called citric acid and vinegar contains acetic acid. These acids like many others are everyday acids. Apart from these there are also laboratory acids, some include; hydrochloric acid, sulphuric acid and nitric acid. 
 
Properties of an Acid
 
Acids have a number of properties. These properties make acidic substances easy to distinguish.
  • Acids are corrosive and have a sour taste.
  • Some acids are more concentrated and stronger then others.
  • Acids have a pH less then 7.
  • Acids change litmus (a dye extracted from lichens) red.
  • Acids react with metals (the more reactive metals) to form hydrogen gas and a salt (neutral).
  • Acids react with carbonates to form carbon dioxide gas, water and a salt (neutral).
  • Acids react with bases to form a salt (neutral) and water. This process is called neutralisation.
  • Acids can conduct electricity.

Neutral Substances

Water is neither an acid nor a base, therefore it is neutral. Other substances that are neutral are classified as salts. Salts have a pH of 7. There are hundreds of different salts and they are named after the acid they are made from. You can see this in the table below. 

 Name of Acid

 Name of Salts

 Examples

 hydrochloric acid

chlorides 

sodium chloride, calcium chloride

 nitric acid

 nitrates

potassium nitrate, ammonium nitrate

 sulfuric acid

sulfates 

copper sulfate, magnesium sulfate

 carbonic acid

carbonates 

calcium carbonate, sodium hydrogen carbonate 

This table was taken from the Science World 9 text book, written by Peter Stannard and ken Williamson. 

The most common salt is sodium chloride or table salt. Other examples include epsom salts used in bath salts, ammonium nitrate used as fertiliser, and baking soda used in cooking

 

 

neutral.jpg
Some common neutral substances

What is a Base?
 
A base is a substance which forms hydroxide (OH- ) ions in a solution. in other words bases are compounds which break up into OH- ions and another compound when placed into a solution (one which is mainly water). Bases which are soluble in water are called alkalis. Some bases are often found in household cleaners, they help clean grease from windows and floors and are found in the soap we use everyday. Some other examples of basic substances are toothpaste, egg whites, dishwashing liquids and household ammonia.
 
Properties of a Base
 
Like acids, bases have properties that make basic substances easy to distinguish.
  • Some bases are more concentrated and stronger than others.
  • Bases feel soapy and slippery.
  • Bases have a pH over 7.
  • Bases react with acids to form a salt (neutral) and water. This process is called neutralisation.
Stomach Acid and Antacid
 
our stomach contains an acid called dilute hydrochloric acid, which breaks down the food we eat. If the contents of our stomach become too acidic, we get indigestion. This can happen when we eat too much or too quickly. To neutralise this excess stomach acid we can take antacid. Antacids are tablets or powders that contain a weak base e.g. baking soda that neutralises the hydrochloric acid. The baking soda also produces carbon dioxide gas. This makes us burp releasing gas trapped in our stomach
 
For my experiment i tested the pH of Eno (antacid) and it had a pH of 6, which should mean it is acidic. This happened because Eno contains citric acid. At the time I did not know what antacids were and used it. However it put an unusual twist to my experiment.
 
 
 

acidfood.jpg
Some common acidic household substances

basefood.jpg
Some common basic household substances

Intel Young Scientist 2004