Arrhenius acid

[inaccensa]

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Are arrhenius acids only strong and moderately strong acids? Extremely weak acid like an alcohol is not an arrhenius acid, since it cant dissociate. It needs a strong base to abstract its proton.

If I have some HCl in a bottle, it doesnt dissociate, but if I have a 50% solution of HCl, then the pH will increase and HCl will be completely dissociated, is this right?
Why do we exactly need water for an arrhenius acid? Does this have to do something with being able to hydrate the ions, while increasing the entropy of solution? Is this an exothermic reaction or an endothermic? Autoionization of water is an endothermic reaction, does this apply to all reactions in water, since we are breaking up h20 molecules?

 

[PingPongPro]

First, calm down. It's probably wisest to ask 1 or 2 questions if you want a better chance of getting your question answered. Most people don't want to answer a dozen of questions, mostly which are tidbits of trivial facts that can be answered via google.

Arrenhius acids/bases are just a way chemists defined acids and bases before bronsted-lowry and lewis better defined what an acid/base was. Just because Arrhenius's acids have a H+ or OH- in their reaction does not mean that they are strong or moderately strong. The strength of an acid does not relate to whether it is an arrhenius, bronsted-lowry, or lewis acid.

"Extremely weak acid like an alcohol is not an arrhenius acid, since it cant dissociate. It needs a strong base to abstract its proton."

These 2 sentences have so many wrong things, I don't know where to begin.

First, weak acids can dissociate (in water). They just don't completely dissociate like strong acids do. Thats what makes them "weak".

Again, being a weak acid does not mean it is not an arrhenius acid. Similarly, an alcohol CAN act as an arrhenius acid. The definition of an arrhenius acid is a substance that increases the H3O+ concentration when dissolved in water. Alcohol does dissociate a little (not completely like a strong acid would), so therefore it can exist as an arrhenius acid.

Pure HCl in a bottle doesn't dissociate (its a gas). I don't know what you mean when you say, "if I have a 50% solution of HCl, then the pH will increase and HCl will be completely dissociated". You cannot compare the pH of the two because HCl does not have a pH. It can't dissociate since it is not aqeuous.

Water is needed for an arrhenius acid because that is the definition of what an Arrenhius acid is. It is something that increases H3O+ concentration in water, so obviously without water, it won't work.

I'm too lazy to answer the other stuff, but all this information can be found in a MCAT study book or on the web. Goodluck.

 

[inaccensa]

The reason I brought this up since EK said that alcohol is not an arrhenius acid