Acids, bases, and water Acids Bases Neutralisation

Acids and bases play a central role in much of the chemistry of every day life. Acids are found in many foods, like citrus fruits, soft drinks and vinegar, while bases are found in cleaning agents and antacids.

Acids, bases, and water
The chemistry of acids and bases most commonly happens in water.

The balance of acids and bases is crucial for our good health and for our environment. If one dominates too much over the other, all sorts of things go wrong and life on Earth would be in peril. Acid rain, fish deaths from acid rain, dirty swimming pools, legionaire bacteria outbreaks and indigestion are all examples of acids and bases being out of balance.

Acids are substances that when dissolved in water release hydrogen ions, H+_(aq).

Bases are substances that react with and neutralise acids, producing water. When dissolved, bases release hydroxide ions, OH-_(aq) into solution. Water is the product of an acid and base reacting. Chemists say that the acid and base cancel or neutralise each other, hence the reaction is known as "neutralisation".

The simple equation for the neutralisation reaction between an acid and a water soluble base is:

H+_(aq) + OH-_(aq) H₂O

Simple neutralisation

Acids
Acids give foods a sour taste. Food acids are weak acids and are not to be confused with the much stronger corrosive laboratory and industrial acids like hydrochloric acid HCl, or sulfuric acid H₂SO₄, which if ingested would be fatal.

Acids react with the more reactive metals to release hydrogen gas and can change the colour of some chemical dyes. We can use this property to test for the presence of an acid in solution.

One such dye, litmus, turns from blue to red in the presence of an acid and is the safest and simplest test for an acid. An acid is a substance that turns blue litmus red.

Bases
Bases are not common in the biological world as the chemistry of life has developed neutral or slightly acidic solutions to deal with most processes. Sodium carbonate and washing soda are properly used household bases. Bases can be either water soluble or insoluble. Insoluble bases react with acids, directly dissolving in the acid as they react. Soluble bases form hydroxide ions in solution, that then react with the acid as described in the above section Acids, bases and water.

Caution: Base solutions are slippery or soapy to the touch. What is happening is the base is reacting with the oils in your skin to form soap, and it is your own oils that you are feeling as they turn into soap! Do not touch bases or get them near your eyes.

Some common bases are sodium hydroxide NaOH, calcium hydroxide Ca(OH)₂ and ammonia solution NH₄OH. Sodium hydroxide is particularly strong base and should not be handled at all.

Bases are substances that neutralise acids and if dissolved in water, turn red litmus blue.

Neutralisation
When an acid and a base are combined, water and a salt are formed. For example, when hydrochloric acid is mixed with sodium hydroxide, water and sodium chloride are formed.

The equation for this reaction is:
HCl + NaOH H₂O + NaCl

Both hydrochloric acid and sodium hydroxide would dissolve you if you fell into them, but you can go swimming in the product of their reaction, salt water! Before you start making your own oceans from acids and bases, remember; it is only when all of the acid has been neutralised by all of the base that you will have neutral salt water. If one or the other is in excess, then the solution will be salty, but it will also be either acidic or basic as well.

Neutralisation

Read the next topic, Measuring acids and bases, for more on neutralisation and acid and base strength.

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