# Acids & Bases --- **Acids** and **bases** are two classes of [[chemistry|chemicals]]. The method used to measure the strength of an acid or base is called the **[[pH]] scale**, which goes from 0-14. The lower the number the more acidic it is, 7 is neutral, and then the higher the number thee more basic it is. Acids and bases are always in [[solution]] (I'm pretty sure). ## The Arrhenius Theory The **Arrhenius theory** was the first theory about what makes an acid and acid, and what makes a base a base. This theory states that acids and bases can be identified by the ions that it has in solution. If it has hydrogen ions, then it is an acid, and if it has hydroxide ions, then it is a base. ## The Brønstead-Lowry Theory The **Brønstead-Lowry** theory describes acid-base interactions in terms of [[hydrogen ion|proton]] transfer between chemicals. This theory expands upon the Arrhenius theory. A Brønstead-Lowry acid *donates* an H+ into solution when they are dissolved, and conversely, a Brønstead-Lowry base *accepts* the H+ in solution when they are dissolved. In this theory, water can be both an acid or a base, depending. ### Conjugate Pairs In the Brønsted-Lowry definition of acids and bases, a conjugate acid-base pair consists of two substances that differ only by the presence of a proton (H⁺). A conjugate acid is formed when a proton is added to a base, and a conjugate base is formed when a proton is removed from an acid. ![[conjugate pair.png]] **Titration** is the process of canceling out an acid or base by adding in some of it's conjugate. ## The Lewis Theory The **Lewis** theory describes acid-base interactions in terms of the transfer between electron pairs. This theory builds on the Brønstead-Lowry theory, and is even more broad, extending into solids and gasses. A **Lewis acid** is a substance that *accepts* a pair of electrons to form a covalent bond. A **Lewis base** is a substance that *donates* a pair of electrons to form a covelent bond. ## Strong & Weak Acids & Bases Strong acids and strong bases dissociate completely in [[solution]]; weak acids and weak bases do not. Inseatead, an equilibrium is formed by the acid and its ions. ![[strong acid.png]] ![[weak acid.png]] Strong Acids | Formula ---|--- [[stomach acid]] | HCl Nitric acid | HNO$_3$ Sulfuric acid | H$_2$SO$_4$ Hydrobromic acid | HBr Hydroiodic acid | HI Perchloric acid | HClO$_4$ Chloric acid | HClO$_3$ Strong Bases | Formula ---|--- Sodium hydroxide | NaOH Potassium hydroxide | KOH Lithium hydroxide | LiOH Rubidium hydroxide | RbOH Cesium hydroxide | CsOH Calcium hydroxide | Ca(OH)$_2$ Barium hydroxide | Ba(OH)$_2$ Strontium hydroxide | Sr(OH)$_2$ ## Buffers **Buffers** are solutions that are a mixture of a weak acid and its conjugate base, or a weak base and its conjugate acid. Buffer solutions resist a change in pH when small amounts of a strong acid or a strong base are added. Note, you cannot mix any two acid/base combination together and get a buffer, both the acid and the base component must be *part of the same equilibrium system*. Single molecules can also act as buffers by binding ty hydrogen or hydroxyl ions. [[protein|Proteins]] act as buffers because they have both the basic amine group and the acidic carboxyl group on them. Our blood and cells are filled with [[blood buffer systems|buffers]] or weak acids to help maintain physiological [[acid-base balance|pH]]. ![[acid and base concentrations.png]] ## Hydronium and Hydroxide **Hydronium** is the word for H$_3$O+ is called **hydronium** and OH- is called **hydroxide**. Another way of thinking about acids and bases is as a ratio of hydronium and hydroxide. Distilled [[water]] is at an equilibiram between a hydronium and a hydroxide. Hydrogen ions are spontaneously generated in pure water by the dissociation (ionization) of a small percentage of water molecules into equal numbers of hydrogen (H+) ions and hydroxide (OH–) ions. ## Acids and Bases in Biology In [[biology]], keeping [[hydrogen ion|H+]] levels within a narrow range is critically important. This is called the [[acid-base balance]], and deviating from it can be harmful. Acidic foods taste better, because we have acid in our [[stomach]] (pH=2). So, eating it works well with the digestive system. Bases would counteract our stomach. After the stomach though, our digestive system is mostly neutral. Human [[blood]] is a little bit basic (much like [[evolution|seawater]]...). More importantly, blood has a buffering system to minimize extreme changes in [[pH]]. ___