Welcome to ChemZipper !!!: LEVELLING EFFECT OF WATER

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When strong acids like HClO4, HCl, HBr, HI, HNO3 etc are dissolved in water they are equally ionised (100%) it means they are equally strong in water this is called levelling effect of water .
Similarly for strong bases also , NaOH, KOH  Ca(OH)2 etc are in water behave the same . hence relative strength of strong acids or base can not be compare in water .
(1) Water does no show levelling effect for weak acids or base because they are ionised upto different extent in water.
(2) All the acids are stronger than H3O+ ion, consider as strong acids and weak than H3O+ ion are consider as weak acids.
(3) All the bases stronger than OH- are consider as strong base and weaker than OH- , then they are consider  as weak base.

DEFINITION: If more than one acids or bases are showing same acidic or basic strength in same solvent it is called labelling effect and the solvent is called labelling solvent.
For example HClO4 and HI equally dessociation in aqueous medium (99.99%)  it means they have equal strength.
Similarly HF and HCl are equally dessociation in NaOH (100 %).
If their strength differ in same solvent ,it is called differential effect and the solvent is called differential solvent

For example HClO4 dessociate 99.99 % in acetic acid while HI dissociate 99.8% in acetic acid, it means acidic strength of HClO4  is more than HI in acetic acid.
The reason behind labelling and diffential  effect is ability of solvent to donate or accept protons .
For acids, acidic solvents are differential and basic solvent are labelling.

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