Okay, acids and bases. Where to begin? Well, defining what acids and bases are would probably be a good place to start.
First up, let's look at some of the basic properties of acids and bases:
Acids
- taste sour, like the citric acid in lemons. I don't recommend testing this by tasting 10M hydrochloric acid, however.
- are corrosive
- neutralise bases
- tend to conduct electricity well
Bases
- taste bitter
- are corrosive
- neutralise acids
- tend to conduct electricity well
But wait, you might say. Acids and bases share so many common properties! They're corrosive, they tend to conduct electricity well, and they neutralise each other! How do you tell them apart?
Well, there are differences at the chemical level. In the past, people have tried to form theories about it. Two of the main ones are the Arrhenius and Bronsted-Lowry theories. (The "o" in Bronsted actually has one of those lines through it, just like in I think Norwegian and Danish and a couple of other languages, but I can't be bothered putting in the effort to find out how to type it.)
Arrhenius' Theory- Acids release H+ ions in water and bases release OH- ions in water. It's a nice and simple theory which explains some properties of acids and bases like pH and neutralisation reactions, but it doesn't explain everything. It doesn't explain why not all bases have OH- ions, and it doesn't account for the fact that the H+ ion actually doesn't last that long in water before it becomes the hydronium ion (H3O+), but it was a pretty useful theory at the time.
Bronsted-Lowry Theory- Acids donate protons while bases accept them. This is based on the idea that a hydrogen ion is actually just a proton (most hydrogen atoms have no neutrons, and H+ ions are hydrogen atoms with one less electron, and since hydrogen only has one electron anyway, H+ ions effectively have no electrons). This is better than the Arrhenius Theory as it accounts for bases which don't have OH- ions, as well as substances that can act as bases AND acids (amphoteric substances- more on them later) but it's still not perfect and that's why some other theory called the Lewis Theory about electron pairs and whatnot was invented, but I don't know enough about the Lewis Theory to be able to teach you.
One more thing about the Bronsted-Lowry theory- the reactants are the acid and base, while the products are the acid with one less proton (or one more H, if you prefer) and the base with one more proton. There are special names for the products: the acid with one less proton is a conjugate base while the base with one more proton is a conjugate acid. Basically the conjugate acid and conjugate base act as the acid and base in the reverse reaction. Well, that's my understanding anyway.
One more way to tell acids and bases apart is through the use of indicators, like Universal Indicator and litmus paper (as well as certain vegetables if I remember correctly). These things change colour when placed into a solution of an acid or a base. Litmus turns red when put into an acid and blue when put into a base. Universal indicator does the same, but it also turns green if the solution is neutral.
Strong and weak acids is up next. Strong and weak acids basically follow the same rules as strong and weak electrolytes, i.e. strong acids completely dissociate or ionise in water while weak acids only partially dissociate in water. Unfortunately I think you more or less just have to remember which acids are strong and which are weak (yeah I hate memorising stuff too). Same goes with the bases. It's not too memory-intensive, though: the hardest part is memorising the strong acids.
As far as I know there are only six strong acids: nitric acid (HNO3), sulfuric acid (H2SO4), hydrochloric acid (HCl), hydrobromic acid (HBr), hydroiodic acid (HI) and perchloric acid (HClO4). All other acids are weak acids.
I think all metal hydroxides are strong bases. All other bases are weak bases.
The last thing I'm going to tell you about today is a few more standard equations to add to your collection.
Acid + Carbonate/Hydrogencarbonate -> Salt + Carbon Dioxide + Water
This is pretty much the same thing as I said in Reactions and Equations, part deux. The only thing now is that I've added hydrogencarbonates/bicarbonates into the mix. Carbonates and hydrogen carbonates react in the same way with acids which makes it easy to remember.
Acid + Metal -> Salt + Hydrogen Gas
A bit more deja vu, isn't it? This is another reaction that I mentioned in Reactions and Equations, part deux, so if you're confused, go read that post, or go Google it and find someone who actually knows how to explain stuff.
Acid + Metal Oxide/ Metal Hydroxide -> Salt + Water
Simple. The metal ion reacts with the anion in the acid to produce the salt, while the hydrogen in the acid reacts with the oxygen in the base to produce the water. This is essentially a neutralisation reaction, as metal oxides and metal hydroxides tend to be bases. (Okay, there are some that are amphoteric- can be an acid OR a base depending on the situation- and they have different reactions, but I'll deal with them later.)
Acid + Base -> Salt + Water
Same thing as I said in Reactions and Equations, part deux. I've realised I made a mistake in that post about suggesting that all bases have OH- ions, which isn't true. I'd say use the above 3 equations if they fit the job description, this one's rather vague in comparison.
Base + Ammonium Salt -> Ammonia + Salt + Water
The cation (positive ion) of the base and anion (negative ion) of the ammonium salt bond to make the salt. Then the N and 3 H of the ammonium ion make the ammonia, leaving behind an H+ ion. This H+ ion bonds with the O(2-) (can't be bothered with superscripts either... too much effort) or OH- ions in the base to make water.
I'll leave the amphoteric metal reactions for another time. TTFN!
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