How Are Strong & Weak Acids Different | Acids, Bases & Alkali's | Chemistry | FuseSchool
Channel: FuseSchool - Global Education
Date: 2016-05-19

Learn the basics about strong and weak acids, and how they differ.

Strong acids are often used in School Science labs for experimentation but they have important uses in industry and the everyday world.

Sulphuric acid for example is found in car batteries but industry uses 200 million tonnes annually for the chemical industry. Hydrochloric acid found in your stomach and nitric acid are also examples of strong acids.

Acids react with water to produce hydrogen ions, or more strictly hydroxonium ions: Strong acids dissociate fully into their ions.

Most acids are weak, and remain largely as molecules in solution. Acids can be identified by using full-range indicator from 0 to 7 on the pH scale. pH is a measure of the concentration of hydrogen ions. 

If you dissolve 1 mole of a strong acid, like HCl in water to make 1litre of solution it dissociates completely into ions so you also get 1 mole per litre of H+ ions, and a pH of 0. To get a solution of pH 4 you have to dilute this with 10,000 times its volume of water. We still have a STRONG acid but it is VERY dilute!

However, if you dissolve 1 mole of a weak acid, like ethanoic acid (also called acetic acid) to make a litre of solution it remains mostly as undissociated molecules.

If an acid is only 0.01% dissociated - so only one molecule in 10,000 are split into ions. Although the concentration of acid is 1 Mole, the concentration of hydrogen ions is only 0.0001 moles per litre, that is 10 to the power negative 4, making the pH 4. So here is an example of a fairly concentrated acid which is weak.

So acids cab be both concentrated and fully dissociated so STRONG, concentrated but not fully dissociated so WEAK, dilute but STRONG because fully dissociated or finally dilute and weak. 

A weak acid can be concentrated and a strong acid can be dilute. Most acids are commonly occurring organic acids such as you find in lemons or vinegar - which are all WEAK so remain mostly as molecules and often have a smell. There are only a few STRONG acids, mostly non-metal oxides dissolved in water like sulfuric and nitric acids, but there is also Hydrochloric acid - found in your stomach to aid digestion!

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