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

Mar 8, 2017

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))^(+)

${H}_{3} {O}^{+}$ indicates that something is acidic

Another way to determine ZnCl2 is acidic is this

$Z n C {l}_{2} + 2 {H}_{2} O = Z n {\left(O H\right)}_{2} + 2 H C l$

$2 H C l + Z n {\left(O H\right)}_{2}$ = 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 = $\frac{430 g}{100 m l}$

First convert 100ml to 1000ml or 1litre

$\frac{430 g}{100 m l} = \frac{4300 g}{1000 m l}$

4300g must converted to moles

$\text{Moles" = "weight"/"molar mass }$

$\text{4300g"/"136.315g}$ = 31.55moles

= 31.55mol/1000ml

Whenever ZnCl2 dissolves it dissolves like this

$Z n C {l}_{2} r i g h t \le f t h a r p \infty n s Z {n}^{+ 2} + 2 C {l}^{-}$

the Ksp expresssion = $\left[Z {n}^{+ 2}\right] {\left[C {l}^{-}\right]}^{2}$

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

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

Ksp = ${\left[\frac{\text{31.55mol"/L] ["63.10mol}}{L}\right]}^{2}$

= 125619.7955 Mar 13, 2017

${\text{ZnCl}}_{2}$ is an acid because $\text{Zn"^"2+}$ 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 The electronegative $\text{Zn"^"2+}$ ion removes electron density from the $\text{O-H}$ 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 ${\text{ZnCl}}_{2}$. The pH was 2.5.