# Intro to Acid/Bases - Tax Evasion # Brønsted-Lowry Definition Acid: proton donor dissociates guaranteed into H+ ion strong acid: fully dissociates in water e.g HCl $H_{2}O + HCl \to H_{3}O^+ \ (\text{conjugate acid}) + Cl^- (\text{conjugate base})$ weak acid: doesn't fully dissociate in water e.g CH3COOH $HNO_{3} + H_{2}SO_{4} \to H_{2}NO_{3}^+ \text{(conjugate acid) }+ HSO_{4}^- \text{(conjugate base)}$ $NH_{3} + H_{2}O \to NH_{4}^+ \ (\text{conjugate acid}) + OH \ \text{(conjugate base)}$ Base: proton acceptor e.g NaOH --> note hydroxide ion! # Lewis Definition Acid: lone pair acceptor base: lone pair donor $OH^- \ (\text{lone pair donor})+ H^+ (\text{lone pair acceptor}) \to H_{2}O$ *Not all lewis acids are brønsted-lowry acids!* $BCl_{3} + NH_{3} \to BCl_{3}NH_{3} \ (\text{generally called an adduct}\\ \text{where a lone pair allows for two molecules to stick without an exchange in hydrogen ions})$ # Arrhenius Definition acid: increases concentration of hydrogen ions base: decreases concentration of OH- ions # rules for bases: 1. atom must have high electronegativity, e.g sodium bad electronegativity, chlorine good electronegativity 2. spreading of changes 1. neighbouring group (group of atoms next to the negative charge) 2. resonance (how the negative charge can move around - is it flexible? ) # finding the PH --> weak acids Note that an acid dissociates into a hydrogen ion and an arbitrary ion (if monobasic) the equilibrium point of the dissociation of an acid $K_a$ (acid dissociation constant) is: $K_{a} = \frac{[H]^+[A]^-}{[HA]}$ where the ion in the square brackets actually tell us the concentration/ppm of each reactant/product typically questions will ask for unknowns (e.g they might not give you the hydrogen concentration! - forcing you to use constants as a temporary measure). the reactants can be found with the (concentration - arbitrary proton concentration) to find the resultant ph plug in formula: $pK_{a} = -\log K_{a}$ therefore if there is an I|C|E table as shown: %%copy ICE table when have time%% %%example question! %% >[!Example]- Example Q pH Questions # buffers --> substance that resists a change in the pH e.g blood :D as blood <u>must</u> have a constant pH or else stuff will happen --> a buffer contains a **weak acid** and its conjugate base - which remain in equilibrium unless external changes happen. --> requires an incomplete neutralisation of a weak acid - e.g CH#COOH - ethanoic acid, as if the concentration of certain ions increases the equilibrium shifts left!!! # le chatelier principle if the concentration of a variable on one side of an equation increases the equilibrium will shift the other way in order to resist it.