What Is The Reaction Of Alcl3 + H2O? Aluminum Chloride Hydrate

You are not adding any hydrogen ions, so why does the pH of the solution decrease? Thank you in advance.

Đang xem: What is the reaction of alcl3 + h2o?

EDIT: I will add the context of my asking this question to clarify some details. This is not a homework question. I am preparing for an upcoming examination in lize.vn, and I found this statement in the mark scheme of a practice exam I was doing, and yet I don”t understand why it is true.

I have learnt pH as simply being the negative log of the concentration of H+ ions. I fail to see how adding the above salt changes the pH, especially since HCl is a strong acid (hence it completely dissociates in solution).

Thought process: Is the pH change a result of Aluminium forming Aluminium Oxide?

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edited Apr 30 “17 at 3:01

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Pritt says Reinstate Monica
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asked Apr 29 “17 at 18:25

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K. T.K. T.
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A more clarified reaction in addition to Berry Holmes” answer:

$$ce{AlCl3 + 4H2O – + 3Cl- + 4H+}$$

The reason this happens is the Lewis-Acidity of $ce{Al^3+}$ as well as the higher affinity for $ce{OH-}$ ions when compared with $ce{Cl-}$.

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edited Apr 29 “17 at 19:45

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orthocresol♦
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answered Apr 29 “17 at 19:09

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tifreltifrel
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When you add $ce{AlCl3}$ to water a reaction takes place:

$$ ce{AlCl3 + H2O Al(OH)3 + HCl} $$

But wait, now I”ve an acid, i.e. hydrochloric acid ($ce{HCl}$) and probably a base ($ce{Al(OH)3}$). Close enough, but $ce{Al(OH)3}$ is actually amphoteric in nature, which means it can behave both as an acid and a base.

Think of it as a tennis match, on one side you”ve a strong player (Novak Djokovic, Roger Federer or Rafael Nadal – you name it) and on the other side you”ve a teen who has barely known tennis for a month. For sure, the strong player is going to win. But which of the two is the strong player in our case?

If you”re guessing it to be $ce{HCl}$, I”ll give you points. I think $ce{Al(OH)3}$ is double minded, it doesn”t know for sure if it”s going to act as an acid or a base. $ce{HCl}$ on the other hand knows that it is a strong acid. $ce{HCl}$ wins the game, making the solution acidic and so, the pH decreases.

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answered Apr 29 “17 at 18:56

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Berry HolmesBerry Holmes
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First of all, $ce{Al^3+}$ will separate itself from $ce{Cl^-}$ in water, due to the nature of this salt (don”t know why, the other answers have included this I believe).

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Because in water, the $ce{Al^3+}$ ion surrounds itself with $ce{H2O}$ molecules, with the partially positively charged H-atoms turned towards the $ce{Al^3+}$.

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With enough electric force pulling all of the $ce{H2O}$ atoms in there will be so many H2O molecules surrounding the $ce{Al^3+}$, all being pulled in by the positive charge, that the molecules are too close together, and eventually one of the $ce{H^+}$ ions is whipped out of this “$ce{H2O}$ circle”.

So $ce{^3+}$ will become $ce{^2+}$ + $ce{H^+}$

Not all $ce{^3+}$ “s will perform this action, and therefore it, like all metal aquo complexes, is a weak acid. For example, it works with $ce{Fe^3+}$ as well.

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edited Apr 29 “17 at 20:02
Mithoron
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answered Apr 29 “17 at 18:52
Daniel GlasDaniel Glas
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