Acid Base 1 : Strength

You must understand that the ACID and the H3O+ it produces, are different things!
The strength of an acid refers to how well (or not) it can produce H3O+ ions.

Strong Acids

Strong acids ionise completely in water to form a high concentration of H3O+ ions.

This means that ALL of the acid will react in water, to produce the full amount of H3O+ ions possible.

Some Strong Acids
• HCl : hydrochloric acid
• HNO3: nitric acid
• H2SO4: sulphuric acid

Example
HCl is known to be a strong acid.
Assume that you had a solution of concentration of 0,5M HCl.
Being strong, all of it would have reacted with water to produce a 0,5M concentration of H+



OR



Weak Acids

Weak acids ionise partially in water to form a low concentration of H3O+ ions.

This means that only SOME of the acid will react with the water, producing a low concentration of H3O+ ions.

Some Weak Acids
• CH3COOH: ethanoic acid
• (COOH)2: oxalic acid
• H2CO3: carbonic acid

Example
Acetic acid is know to be a weak acid.
Assume that you have a solution of acetic acid of concentration 0,5M.
Being weak, only some of the acid will react, producing a low concentration of H3O+ ions.

Notice that 0,5M solution of acid produces only 0,01M of H+ ions.



OR



Weak acids do NOT follow stoichiometric mole calculations. Notice that the concentrations are NOT in keeping with the mole ratios of the actual equation.

Strong Bases

Strong bases dissociate completely in water to form a high concentration of OH- (hydroxyl) ions.

This means that all the base added to water, will dissociate producing hydroxyl ions.

Some Strong Bases
• NaOH: sodium hydroxide
• KOH: potassium hydroxide
• Ba(OH)2: barium hydroxide

Weak Bases

Weak bases dissociate / ionise incompletely in water to form a low concentration of OH- ions.

This means that only some of the base when added to water, will actually produce hydroxyl ions.

Some Weak Bases
• NH3: ammonia
• CaCO3: calcium carbonate
• NaHCO3: sodium hydrogen carbonate
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