Why is #ZnCl_2# is an acid though it does not have a #H^+# or a #OH^-#?

2 Answers

ZnCl2 is a Lewis acid because of the following reasons

Zn+2 is a Lewis acid

the chlorine does not hydrolyze so the equation would be like this

#["Zn"("H"_ 2"O")_ 6]_ ((aq))^(2+) + "H"_ 2"O"_ ((l)) rightleftharpoons ["Zn"("H"_ 2"O")_ 5("OH")]_ ((aq))^(+) + "H"_ 3"O"_ ((aq))^(+)#

#H_3O^+# indicates that something is acidic

Another way to determine ZnCl2 is acidic is this

#ZnCl_2 + 2H_2O = Zn(OH)_2 + 2HCl#

#2HCl + Zn(OH)_2# = acidic solution because of HCl is a strong acid so ZnCl2 is acidic.

6M of ZnCl2 has a pH of 3 - 4

Ksp of ZnCl2 cannot be found on the internet so i think to solve from ZnCl2 solubility in water

Solubility of ZnCl2 = #(430g)/(100ml) #

First convert 100ml to 1000ml or 1litre

#(430g)/(100ml) = (4300g)/(1000ml)#

4300g must converted to moles

#"Moles" = "weight"/"molar mass "#

#"4300g"/"136.315g"# = 31.55moles

= 31.55mol/1000ml

Whenever ZnCl2 dissolves it dissolves like this

#ZnCl_2 rightleftharpoons Zn^(+2) + 2Cl^-#

the Ksp expresssion = #[Zn^(+2)] [Cl^-]^2#

The molar ration of 2Cl- to ZnCl2
= 2 : 1

Therefore concentration of 2Cl- is 31.55 * 2 = 63.10mol/L

Ksp = #["31.55mol"/L] ["63.10mol"/L]^2#

= 125619.7955

ZN(OH)5(OH)+

Answer:

#"ZnCl"_2# is an acid because #"Zn"^"2+"# ions are Lewis acids.

Explanation:

The zinc ion can accept six electron pairs to form a hydrated zinc ion.

#"Zn"^"2+""(aq)" + "6H"_2"O""(l)" → underbrace(["Zn"("H"_2"O")_6]^"2+""(aq)")_color(red)("hexaaquazinc(II) ion")#

The structure of the hydrated ion is

Structure

The electronegative #"Zn"^"2+"# ion removes electron density from the #"O-H"# bonds.

The bonds become weaker, so the water ligands become more acidic.

The aqueous solution forms hydronium ions through reactions like this:

#["Zn"("H"_2"O")_6]^"2+""(aq)" + "H"_2"O(l)" ⇌ underbrace(["Zn"("H"_2"O")_5("OH")]^"+""(aq)")_color(red)("pentaaquahydroxozinc(II) ion") + "H"_3"O"^"+""(aq)"#

I asked a chemist friend to prepare a 6 mol/L solution of #"ZnCl"_2#. The pH was 2.5.