What Are Acids and Bases?
Maybe you’re in a high school chemistry class, or maybe you just rewatched Alien and saw the blood eat through the floor. Or you’re just a curious soul who’s very invested in what acids and bases are. Regardless you’ve asked the question so we’ll answer it.
There are three types of acids and bases, but before we get into that we’ll define some base concepts.
Chief among them is the pH scale. There’s some math that goes into determining the pH of a solution (liquid mixture), but basically it tells us how acidic or basic a water-based solution is. An acidic solution has a low pH and a basic one has a high pH. The scale goes from 1-14, so a neutral solution (think water at room temperature) has pH 7.
If you wanna take a litmus test, acids tend to be sour and bases are bitter. Don’t eat anything from a lab, but this is why citrus fruits are sour. They contain citric acid.
Technically that’s a litmus taste, but we digress.
Strong Acids and Bases
If you’re discussing acids and bases, you’ve probably heard the term “strong acid” or “strong base.” This doesn’t actually have all that much to do with how quickly the acid or base will eat through your skin or floor though. For example, hydrochloric acid (HCl) is a strong acid, and hydrofluoric acid (HF) is weak. However, we’d much rather touch the HCl. Bear in mind that at higher concentrations HCl still isn’t something you want to be touching. General rule, don’t stick your hand in acids or bases.
So if it doesn’t have to do with how quickly it eats you, what are strong acids and bases? Well first off, acids and bases don’t eat things. They break them apart.
Semantics aside, acid/base strength is determined by how readily the given acid or base dissolves in water. We’ll bring back HCl as the strong acid and use acetic acid as the weak one. When you dump HCl in water, you get only hydrogen and chlorine ions. There will be no HCl molecules in your solution. That’s why it’s a strong acid.
Conversely, a weak acid like acetic acid doesn’t dissociate completely. Acetic acid dissociates into hydrogen ions and acetate. If you stick it in water, there will still be some acetic acid with the ions and acetate, because it hasn’t dissociated completely like the strong acid did.
The same rules of thumb apply to bases.
Acid and Base Types
There are three types of acids and bases. Each category applies to both, so we’ll get into it now. We’ll use water as our example, which you should know is H2O. Water dissociates into hydrogen ions (H+) and hydroxide ions (OH–). When we look at defining an acid or base, things that are positively charged (H+) are acidic, while negatively charged things are basic (OH–).
Fun fact about water, since it creates both acidic and basic components in equal amounts. Technically a cup of pure water has H2O, H+, and OH–, but the latter two also react with each other to create H2O again. The solution will always have equal parts acid and equal parts base, hence why water is neutral pH 7.
We call things that have acidic and basic properties amphoteric. Have fun impressing people by telling them you’re drinking an amphoteric molecule next time you have a glass.
Arrhenius Acids and Bases
Coined by Svante Arrhenius, Arrhenius acids create H+ ions when they’re placed in water. Arrhenius bases create OH–. So with our example of water, it creates both H+ and OH–, and is therefore both an Arrhenius acid and base. We previously used HCl, which dissociates into H+ and Cl–. Therefore, HCl is an Arrhenius acid, but not an Arrhenius base.
Bronsted-Lowry Acids and Bases
A Bronsted-Lowry acid donates H+ in solution, while the base accepts H+. So using HCl, it “donates” H+ in solution because that’s what it dissociates into. When you put it into a chemical reaction, that H+ will react with something that “accepts” it. Ergo, when H+ is present in solution with OH–, you get H2O. The HCl would have “donated” the ion to the OH–. So the HCl is our acid, while the OH– is the base.
Lewis Acids and Bases
Instead of being relative to H+, Lewis acids and bases are relative to electron pairs. Basically they donate and accept the “-” part in a chemical equation. Acids accept this time, where bases donate.
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