Acids and Bases Chapter 16

Pre-Chapter Questions 1. What is meant by the term acid? Name two products you think are acidic. 2. What is meant by the term base? 3. What do you know about the pH scale?

Acids - 3 types of naming Formula to name: from the ion sheet, if the negative ion has no oxygen (ends with -ide) use root (usually 1st syllable) -ide hydro_____ic acid if it has oxygen, then it ends either -ate or -ite -ate _____ic acid -ite _____ous acid HBr HNO 3 HNO 2 H 2 CrO 4

Acids - name to formula Name to formula: 1st: change hydro___ ic back to -ide or -ic acid back to -ate or -ous back to -ite 2nd: find the name on the ion sheet and its charge, 3rd: add enough H +1 to make neutral Remember write formula without charges! hydroiodic acid sulfuric acid oxalic acid nitrous acid

Properties of acids and bases Acids Sour pH <7 Conduct electricity –Dissolved in water Corrode metals Bases Bitter pH >7 Conduct electricity –Dissolved in water Used in cleaners Soaps / slippery

What are acids and bases? Different ways to catagorize them –An acid produces hydrogen ions (H + ) –A base produces hydroxide ions (OH - ) Or more general definition –An acid is a proton (H + ) donor –A base is a proton acceptor

Bronsted-Lowry Model HA(aq) + H 2 O(l)  H 3 O + (aq) + A - (aq) Acid base conjugate conjugate acid base A conjugate acid-base pair is a pair of substances related to each other by the donating and accepting of a single proton. –H 3 O + is called the hydronium ion

Acid/Base Pairs

Strength of acids A strong acid is an acid that completely ionizes (dissociates) when dissolved A weak acid most of the acid remains HA

STRONG ACIDS HCl HBr HI H 2 SO 4 HNO 3 HClO 4 In general 2 more O than H in parent acid

strong acid / weak conj base The conjugate base of a strong acid doesn’t compete much with H 2 O for the proton - water is a stronger base

Water just can’t decide… Water can be both an acid and a base –Amphoteric substance Water can even interact with itself! Pure water... [H + ] and the [OH - ] are the same concentration [H + ] = [OH - ] = 1.0 x FYI… [ ] means molarity, or concentration

H 2 O(l) + H 2 O(l) H 3 O + (aq) + OH - (aq) What is the equilibrium constant for this reaction? K = [H + ][OH - ] = 1 x K w the ion-product constant for water. It means that in any aqueous solution at 25˚C, no matter what the solution contains, the product of [H + ] and [OH - ] must equal 1 x

THEREFORE… If [H + ] = [OH - ], the solution is neutral. If [H + ] > [OH - ], the solution is acidic If [H + ] < [OH - ], the solution is basic. In any case, the product of [H + ] and [OH - ] will be 1 x

Determining Acid Strength When dealing with acids and bases, we’re dealing with really small numbers for concentrations. Need some other way to describe acid strength. pH Scale!

The pH scale

pH Scale pH is based on a logarithm, base 10 pH = -log [H + ] Remember: [ ] means concentration

What about bases? Just do the same thing, only with OH -. pOH = -log [OH - ] pH + pOH = 14.00

Undoing the pH

Measuring pH Indicators –substances that exhibit different colors in acidic and basic solutions –generally weak acids themselves, H I n –H I n + H 2 O = H 3 O +1 + I n -1 litmus Paper (blue & red), pH paper pH Meters Cabbage juice

Titrations and Buffers A few definitions… Titration – delivering a measured volume of a solution of known concentration into the solution being analyzed Titrant – a standard solution Buret – device used for accurate measurement of the delivery of a liquid Stoichiometric point (equivalence point) – when just enough titrant has been added to react with all of the solution being analyzed

Titration apparatus 22

Consider the following… How many moles of H + can be donated by the following acids: –HCl –H 2 CO 3 –H 3 PO 4 So, if I have 1 mol of each acid, I have a different amount of H + Need to consider how many H + ’s or OH -1 ’s are in the compounds when reacting them together. Balance the neutralization reaction.

All about buffers Buffered solution – resists a change in its pH when either and acid or a base has been added –Presence of a weak acid and its conjugate base buffers the solution Blood is a carbonic acid buffer

How a Buffer works