3：Three. Acids, Bases and pH - Collin College.ppt

? Water molecules can dissociate and ionize when a hydrogen atom shared by two water molecules in a hydrogen bond shifts from one molecule to the other. The electron of the hydrogen atom is not transferred, only a single proton. This single proton is referred to as a hydrogen ion (H+), with a charge of +1. the water molecule that lost the proton es a hydroxide ion (OH-) with a charge of -1. the water molecule bonding to the hydrogen ion es a hydronium ion (H3O+) with a charge of +1. The chemical equation is written: 2 H2O H3O+ + OH – To simplify the equation, by convention we write: H2O H + + OH - 1 ? A solution that has equal concentrations of H+ and OH- is said to be neutral . ? An acid is a substance that dissociates when dissolved in water, producing H+. Hydrochloric acid is a strong acid. HCl H+ + Cl- ? A base is a substance that, when dissolved in water, reduces the hydrogen ion concentration. Some bases do this by donating OH- that interact with H+ to form water. Sodium hydroxide is an example of a strong base. ? NaOH Na+ + OH- 2 ? A measure of the power of the hydrogen ion concentration in a solution is known as pH. pH= - log ?? [H+] ? The pH scale ranges from 0-14 for biological systems. At neutrality, the hydrogen and hydroxide ion concentration is 10 ?? M. Therefore, at neutrality pH is equal to 7. There is an inverse relationship between pH and hydrogen ion concentration; that is, as the hydrogen ion concentration increases, the pH decreases, and vice versa. 3 ? Base: dissociates hydroxide ions into solution or accepts hydrogen ions pH above 7 ? Acid: dissociates hydrogen ions into solution pH below 7 4 ? It is very important for anisms to maintain a pH around - . ? Buffers are special solutions that can help maintain pH by resisting any changes to pH caused by the addition of an acid/base. ? Buffers are solutions of weak acid/weak base. An example is carbonic acid/bicarbonat