Acids Things to know, if you plan to fight aliens... What You've Probably Learned Most of you have probably seen something like this: Some Questions 1. What kind of an idiot comes up with a scale that makes 7 neutral? 2. What does pH actually mean? How much stronger is pH 1 than pH 2? 3. What even makes something an acid or base in the first place? In Reverse Order 3. What even makes something an acid or base in the first place? vs ArrheniusBronsted Arrhenius 3. What even makes something an acid or base in the first place? An acid is something that increases the concentration of H + when put in water A base is something that increases the concentration of OH - when put in water Arrhenius Bronsted 3. What even makes something an acid or base in the first place? An acid is something that gives away an H + A base is something that gets an H + (this actually makes very little difference, since if you have a base, and it gets an H + from water, it leaves behind....OH - !) Bronsted In Reverse Order 3. What even makes something an acid or base in the first place? Lewis (his is actually the most general definition, but only needed in very unusual cases) Strong and Weak Acids If I take a generic acidcall it HAand put it in water, it splits apart: HA (aq) H + (aq) + A - (aq) This is what actually makes it an acid in the first place (see previous definitions) If it's a strong acid, this happens completely. If it's not 100%, then it's weak These are your common strong acids. Know them: HClHNO 3 H 2 SO 4 (HBr, HI, and HClO 4 are some less common ones) Continuing in Reverse Order 2. What does pH actually mean? How much stronger is pH 1 than pH 2? pH = -log[H + ]Square brackets mean concentration (If you have not yet done logarithms in math, see me for a quick tutorial) So, if I have a 0.1 M HCl solution, then [H + ] = 0.1 M -log(0.1) = 1So it's pH 1 If I have a 0.01 M HCl solution, then [H+] = 0.01 M -log(0.01) = 2So it's pH 2 (We'll do bases later) Last One 1. What kind of an idiot comes up with a scale that makes 7 neutral? This comes from the fact that even completely pure water breaks apart a little bit: H 2 O (l) H + (aq) + OH - (aq) No matter what, the following is true:[H + ]*[OH - ] = If we haven't added any acid or base, then both [H + ] and [OH - ] are pH = -log(10 -7 ) = 7 So pH 7 is neutral because that's how much H + you have in completely pure water, which has the same amount of acid and base in it (a very very tiny, miniscule amount). Summary Acids give H +, bases get H + (and make OH - in water) Strong acids completely break apart into H + and something negative HCl, HNO 3, and H 2 SO 4 are the most common strong acids pH = -log[H + ] [H + ]*[OH - ] = which is why neutral is pH 7 If you have to fight an alien on an interstellar mining ship, watch out for the acidic blood.