T&T: Acid dilution WARNING

[Richard Quarles]

> Message: 11
> Date: Sun, 27 Jan 2008 09:17:22 -0800
> From: Candy Chapman and Gary Bell <tulgey at earthlink.net>
> Subject: T&T: Acid dilution WARNING
> To: T & T <trawlers-and-trawlering at lists.samurai.com>
> Message-ID: <479CBCA2.3010600 at earthlink.net>
> Content-Type: text/plain; charset=ISO-8859-1; format=flowed
> Sorry, no disrespect intended here, but Very Wrong Answer, although  
> you are of
> course logically correct about the concentrations.  The HUGE reason  
> to NEVER
> add water to any acid is that the water molecule is almost  
> instantly broken
> apart into ions (H+ and -OH), and that reaction is quite exothermic  
> -- it
> releases a LOT of energy in the form of heat.  As you first begin  
> to add
> water, the still strong acid solution can instantly boil, often  
> appearing like
> an explosion.  Lots of splashing, and you don't have to jiggle it.
> Exceptionally Bad News.  In labs, industry and commerce acid  
> dilution is
> ALWAYS done acid into water, and is invariably done with safety  
> equipment like
> face shields, acid proof gloves, aprons/smocks and shoe covers/ 
> boots.  Of
> course the amount of heat released depends on the concentration of  
> the acid
> and the amount of water added: so if your already diluted muratic  
> acid (in
> this case) is very dilute, and/or the water added verrrry slowly and
> carefully, perhaps under controlled conditions with a thermometer  
> to measure
> the inevitable temperature rise, you could get away from the  
> consequences of
> breaking one of the primary safety rules of chemistry.  Or perhaps  
> not...  I
> know, everyone would rather pick up a vessel of water to pour,  
> rather than one
> of acid, but the consequences can sometimes be dire.  Please cover  
> your eyes,
> use rubber gloves, and pick a safe place to do this.  In the case  
> of topping
> up batteries on a boat, you have little realistic choice, and  
> honoring the
> reality that the sulpheric acid in a wet cell battery is quite  
> concentrated,
> please wear some appropriate safety stuff, dribble the water in  
> slowly, and
> don't put your face where splatters could come out.
>
> The surprisingly excitable Mister Science.
>
Dear Mr. Science,

You are absolutely wrong on this subject.  Slowly adding water to  
concentrated acid the the bestg way I know of to get thoroughly  
spattered with acid.  If you must add the water to the acid (and I've  
seen numerous occasiions where it was necessary) you should add the  
water as rapidly as possible to provide a large heat sink to prevent  
the boiling.  The heat is generated by the water molecuels trying to  
hydrate the already existing hydrogen iions in the acid.



Rick Quarles
Barric II, Nordic Tug 32-147
New Bern, NC