Chlorine Oxoacids — Complete Reference
Acidic strength: HOCl < HClO 2 < HClO 3 < HClO 4 \text{Acidic strength: HOCl} < \text{HClO}_2 < \text{HClO}_3 < \text{HClO}_4 Acidic strength: HOCl < HClO 2 < HClO 3 < HClO 4
Acid Formula Oxidation State of Cl Salt Stability Hypochlorous acid HOCl \text{HOCl} HOCl Cl = + 1 \text{Cl} = +1 Cl = + 1 Hypochlorite (OC l − Cl^{-} C l − Least stable Chlorous acid HClO 2 \text{HClO}_2 HClO 2 Cl = + 3 \text{Cl} = +3 Cl = + 3 Chlorite (ClO2^{-}) Unstable Chloric acid HClO 3 \text{HClO}_3 HClO 3 Cl = + 5 \text{Cl} = +5 Cl = + 5 Chlorate (ClO3^{-}) Moderately stable Perchloric acid HClO 4 \text{HClO}_4 HClO 4 Cl = + 7 \text{Cl} = +7 Cl = + 7 Perchlorate (ClO4^{-}) Most stable, strongest acid
Why does acidic strength increase with oxidation state?
More O atoms ⇒ Greater inductive/resonance withdrawal from O-H ⇒ Weaker O-H bond ⇒ Easier H + release \text{More O atoms} \Rightarrow \text{Greater inductive/resonance withdrawal from O-H} \Rightarrow \text{Weaker O-H bond} \Rightarrow \text{Easier H}^+ \text{ release} More O atoms ⇒ Greater inductive/resonance withdrawal from O-H ⇒ Weaker O-H bond ⇒ Easier H + release
More O atoms ⇒ Better delocalization of negative charge in conjugate base ⇒ More stable conjugate base ⇒ Stronger acid \text{More O atoms} \Rightarrow \text{Better delocalization of negative charge in conjugate base} \Rightarrow \text{More stable conjugate base} \Rightarrow \text{Stronger acid} More O atoms ⇒ Better delocalization of negative charge in conjugate base ⇒ More stable conjugate base ⇒ Stronger acid
Fluorine exception:
F has no oxoacids because: { No d-orbitals available Highest electronegativity → only negative oxidation states Cannot form bonds with O that require positive oxidation state \text{F has no oxoacids because:} \begin{cases} \text{No d-orbitals available} \\ \text{Highest electronegativity → only negative oxidation states} \\ \text{Cannot form bonds with O that require positive oxidation state} \end{cases} F has no oxoacids because: ⎩ ⎨ ⎧ No d-orbitals available Highest electronegativity → only negative oxidation states Cannot form bonds with O that require positive oxidation state
Bleaching powder preparation:
Ca(OH) 2 + Cl 2 → CaOCl 2 ⏟ CaOCl 2 = Ca 2 + ( Cl − ) ( OCl − ) + H 2 O \text{Ca(OH)}_2 + \text{Cl}_2 \rightarrow \underbrace{\text{CaOCl}_2}_{\text{CaOCl}_2 = \text{Ca}^{2+}(\text{Cl}^-)(\text{OCl}^-)} + \text{H}_2\text{O} Ca(OH) 2 + Cl 2 → CaOCl 2 = Ca 2 + ( Cl − ) ( OCl − ) CaOCl 2 + H 2 O