Acid-base equilibria

Read our general notes on Risk Assessment

How can you predict whether an acid is strong or weak from its formula?
 

Igloo writes
 
The strength of an acid, i.e. whether it is “strong” or “weak”, depends on the extent to which it ionises in a solvent such as water.
 
Strong acids are regarded as being totally ionised, whereas weak acids are defined as those which are only partially ionised in aqueous solution.
 
This ionisation process involves the loss of a proton (H⁺) from a molecule of the acid, and the readiness to which this happens depends in turn on the ability of the rest of the molecule to lose this ion. At AS level you do not need to know the factors which would enable you to predict the strength of an acid, given its formula.
 
There is no simple rule for predicting whether or not an acid will be strong or weak from its formula. There are some guidelines that are helpful:

for non-metal oxoacids the higher the oxidation state of the non-metal the stronger the acid so H₂SO₄ is a strong acid while H₂SO₃ is a weak acid (and you will see the same pattern for the oxoacids of nitrogen, phosphorus and chlorine)

Risk assessment
Before attempting any practical work based on the advice and suggestions on this website, you must do the following. Identify any hazards, assess the risks from these hazards, and then decide appropriate control measures to reduce the risks. You must have these approved by those in authority in your school or college laboratory. Do not rely on what is said on this website. For further guidance see our tutorial on Risk Assessment.

back to Acid-base equilibria

---

Rate this page or react
Share your views on this page, 6 ratings so far , rated at

---

updated: 07 January 2004