Why do acids and bases only react with each other in water?

Question

This is a question that I must answer for a prac report in chemistry. I asked this question once before on Yahoo Answers and people said it wasn't true. I don't understand why we'd be asked to specifically answer this question if it wasn't true.

Even if there are some rare cases in which water does not need to be present, why do bicarb soda and citric acid only react with each other in water?

Answer 1

This is because putting the acids and bases into water dissociates them. Take for example HCl and NaOH, two very common substances. If you prepare an aqeous solution of these they will separate into their component ions, H+ and Cl- and Na* and OH-. When the ions are free to move about they are free to interact with other ions in a chemical reaction. Think back to an electrochemical reaction you might have observed in grade school. Solid salt doesn't conduct electricity so the light bulb stays dim, but when you use a solution of salt and water the bulb lights up. This is because the ions are free to move.

The reason why people probably said this wasn't true before was that they would use acids and bases in class and not have to add water to them. They probably weren't cognizant of the fact that they were likely aqueous solutions with water already added. Rarely do we use concentrated acids and bases for reactions; we usually dilute them.

Answer 2

They don't.

Acids and bases will generally react in water due to the dissociation of the ions. However any solute that will dissolve both will cause a reaction. Some reactions can even take place with out a solute.

Reasons for the reaction in a fluid medium is that the molecules will dissociate move around and react easier. Another reason is that a lot of the classical acids are formed via a gas dissolved in water ( ie sulphuric acid is sulphur trioxide dissolved in water). Water is just a convenient solute to use in most cases.

An example of an acid base reaction without water is the formation of Nylon. You take a Carboxylic acid (acid) dimer and an amine dimer (base). If you are careful you can pour one on top of the other so that the two ingredients only meet at the interface. If you take a hook and pass it through the interface and then draw it out slowly you will extrude a length of nylon polymer as the acid base reaction takes place at the interface.

Addition.
The classic way of making an amide is by adding an amine to a carboxylic acid. This is an acid/base reaction although the mechanism is slightly different to say HCl and NaOH.

You can make an amide by using an acid halide but the reaction can be violent and difficult to control

Nylon 6,6 can be formed by hexandioic acid and 1,6 hexadiamine. There is no acid chloride involved in this reaction.
Source: Organic chemistry by Fessenden and Fessenden

PS: I strongly doubt that acetic acid and triethylamine will react as the amine is tertiary and sterically hindered.

Answer 3

Who says that they do? The OH - Ions and H+ ions interact with the water molecules quite a bit too. It's all about averages. Water doesn't have a natural PH of 0. It has a natural PH of 7. This means that water molecules are turning into H+ ions and OH- ions all of the time. In fact this is happening billions of times every second inside of your body. Sorry if that's not a simple answer, but it's a pretty interesting subject IMHO. May the wind be always at your back, -Empyrealmortal

Answer 4

For solid acids and bases, you need a solvent to allow for disassociation of the molecules.

However, you do not need water or solvent for ALL acids and bases. Mix two liquids such as triethylamine and acetic acid together and you will get a reaction, w/ no water present.

Finally, the nylon poster mischaracterized the synthesis of nylon. It's not a neutralization reaction, its an amide synthesis between an acid chloride and an amine If you mixed a carboxylic acid with a base, you simply neutralize, w/o forming nylon. Besides, the classic lab reaction uses methylene chloride and water to create two separate phases, so yes, water is present.

Answer 5

In solution, acids and bases dissociate. That is, acids will give H+ (or in the case of a aquoues solution, will give H3O+) and bases will give OH-. It is the H+ and the OH- which react in a acid base neutralization to form water. If they weren't in solution, and in solid form, if u put them together in a beaker and shake them together, nothing will happen because the H+ and the OH- are not free to react.
Without water, neither the acid nor the carbonate can dissociate. If there is no dissociation, the
effervescent reaction cannot start.

Answer 6

In water, the H+ ions dissociate and are free to move around and react. In solid acids, they are often stuck in their molecules.