310 likes | 324 Views
Explore the significance of acids and bases in various contexts such as food, cleaning products, pharmaceuticals, and more. Understand their properties, strengths, and how they affect pH levels. Learn about the concept of buffered solutions and their role in maintaining a constant pH.
E N D
Chapter 16 acids and bases
are acids important? boy howdy! • lemons, heartburn, digestion, cavities, pools, cleaners, etc., etc., etc. • sulfuric acid alone is used to make fertilizers, detergents, plastics, pharmaceuticals, batteries, metals… • here we hit the highlights of acids and bases…
16.1 acids and bases • acids were first known for their sour taste (think vit c, vinegar, lemons, vomit, underarm juice, orange juice, bad milk • bases (alkalis) are known for their bitter tastes, and slippery feel; most soaps are basic
the arrhenius model • svante arrhenius was the first guy to try and figure out what was going on chemically; he found: • acids produced H+ ions in aq solns • bases give us hydroxide (OH-) ions
16.1 • HCl(g)H+(aq) + Cl-(aq)this is the strong acid (hydrochloric)or… • NaOH(s) Na+(aq) + OH-(aq)this is a strong base • but there is a better way of looking at it…
the brønsted-lowry model • the brønsted way of things looked at it this way: • acids DONATE protons (H ions) • bases ACCEPT protons EZ!
16.1 • assume our acid is HA; then… • HA + H2O H3O+ + A- • what happened to HA? • it lost an H (proton); it acted acidic • what happened to water? • it gained a proton; it acted as a base
16.1 • when the HA lost its H it went from acid to base; i.e. it could get the H back at some other time • when an acid loses an H it becomes a conjugate base • when water gained a proton to become H3O+ it became an acid • called conjugate acid
16.1 • a conjugate acid-base pair differs just by one single H: • HCl/Cl- • H2O/H3O+ • NH4+/NH3 • BTW; H3O+ has a special name; hydronium ion
16.1 • can you see each of these rxns are acid-base rxns? • can you ID the conjugate pairs?
16.2 acid strength • some acids dump every H they can • they are completely ionized • = strong acids • some acids hold on tomost their Hs • they are only partially ionized = weak acid
16.2 strong weak
16.2 strong weak
16.2 • some acids have 2 protons that can be lost • = diprotic acid • e.g. H2SO4 • most acids are oxyacids, i.e. the proton to be lost is hooked up to an O • e.g. HNO3, HOCl, H2SO4, H3PO4
16.2 • some of the most common acids are organic acidswhich have a carboxyl group hooked up to them • –C–O–H || O • these critters are weak (e.g. acetic acid (vinegar), formic acid (ant bites), citric acid, vitamin C, aspirin
16.3 water as an acid and a base • water can accept a proton (to become hydronium), or… • donate a proton (to become hydroxide ion) • acts as both acid and base!!! • called amphoteric • water can actually self-ionize!…
16.3 H2O + H2O H3O+ + OH– • this hardly happens at all (thankfully) • important toknow here thatit does happen,and even purewater has someacids and basesfloating around init…
16.3 • a soln is acidic if [H3O+] > [OH-] • a soln is basic if [H3O+] < [OH-] • a soln is neutral if [H3O+] = [OH-] • important to see here that whatever the soln is there’s always some of the enemy in there
16.4 the pH scale • fyi: [H3O+] is also known as [H+] • the pH scale is an easy way to see how acidic or basic a soln is • mathematically: pH = –log[H3O+] • if I give you the [H3O+] you can figure out the pH of the soln by: • entering the [H3O+], taking the log, and changing the sign (+/-)
example • what is the pH if the [H3O+] = 0.001 M • pH = 3 • pH if the [H3O+] = 0.000021 M • pH = 4.68 • pH if the [H3O+] = 0.000000059 M • pH = 7.23
16.4 • every change of one pH unit = 10x acidic concentration change • pH > 7 basic • pH = 7 neutral • pH < 7 acidic
16.4 • to find the [H3O+] from pH do opposite • enter pH; change sign; take inverse log! • so if pH is 8.53… • change sign (-8.53) • take inv log (3.0 x 10-9 M)
16.5 measuring pH • a couple ways we have to measure pH • one way involves indicators, things which change colors in the presence of different [H3O+]…
16.5 • some indicators can be put on paper, we can read colors to determine pH • eg. Litmus paper (red in acid, blue in base)
16.5 • a really accurate way of doing it is with a pH meter
16.8 buffered solutions • a buffered solnresists a change in pH even when a strong acid or base is put in it • especially important to living critters whose bio systems require a cnst pH • how does it work?
16.8 • a soln contains a weak acid HA, and its conjugate base A- • when we dump in extra acid or base these two gobble it up: • the A- reacts with the extra protons to become HA • the HA reacts with the extra OH- to become A- • overall there is little change in pH!!!