Acids and Bases Chapter 10

Acid-Base Theories Properties of Acids and Bases Arrhenius Acid-Base Theory BrØnsted-Lowry Acid-Base Theory strong and weak acids and bases acid nomenclature review

Properties of Acids and Bases Acids taste sour conduct electricity in aqueous solution turn litmus red react with carbonates to produce CO 2 (g) react with active metals to produce H 2 (g)

Examples of Acids citric acid ascorbic acid lactic acid carbonic acid muriatic acid (aka: hydrochloric acid)

Bases feel slippery taste bitter turn litmus blue do not react with carbonates or with active metals

Examples of Bases drain cleaner and oven cleaner (NaOH) baking soda (NaHCO 3 ) washing soda (Na 2 CO 3 ) glass cleaner (ammonia, NH 3 (aq)) Na 3 PO 4 (aka “TSP”)

Arrhenius Theory of Acids and Bases Acids ionize in water to produce hydronium, H 3 O + (aq), ions. eg. This is an ionization reaction. HCl(g) + H 2 O(l)  H 3 O + (aq) + Cl − (aq) HCl(aq)

writes this equation as: HCl(g)  H + (aq) + Cl − (aq) NB. The H + ion does not exist as such in aq solution. The hydronium ion is a hydrated proton, H +.

some fine print... Some texts, like ours, abbreviate the hydronium ion, H 3 O +, as H +, called a hydrogen ion. This is inaccurate! H + is a bare proton—which cannot exist in water. Take a look...

the aqueous hydronium ion: What is the geometry of the hydronium ion? pyramidal

Bases dissociate in water to produce one or more hydroxide, OH – (aq), ions. eg. This is a dissociation reaction. Na(OH)(s)  Na + (aq) + OH – (aq) Ba(OH) 2 (s)  Ba 2+ (aq) + 2OH – (aq)

Limitations of the Arrhenius Theory restricted to acids & bases in aq solution doesn’t explain behaviour of all acids or bases doesn’t explain certain types of neutralization reactions NH 3 (g) + HCl(g)  NH 4 Cl(s)

BrØnsted-Lowry Acid-Base Theory Acid: proton (H + ) donor Base: proton (H + ) acceptor not restricted to aq. solutions Explains NH 3 (g) + HCl(g)  NH 4 Cl(s) (note that N in NH 3 has a lone pair of e - s)

In order to qualify as a B-L acid, a compound must contain _____________. (hydrogen) In order to qualify as a B-L base, a compound must contain ______________. (lone pair of e – s— or a negative charge)

Some B-L Acids & Bases HCl(g) + H 2 O(l)  H 3 O + (aq) + Cl − (aq) B-L acid B-L base NH 3 (aq) + H 2 O(l) NH 4 + (aq) + OH − (aq) B-L base B-L acid Water can act as either a B-L acid or base; water is amphiprotic.

Conjugate Acid-Base Pairs HCl(g) + H 2 O(l)  H 3 O + (aq) + Cl − (aq) B-L acid B-L base conj acid conj base NH 3 (aq) + H 2 O(l) NH 4 + (aq) + OH − (aq) B-L base B-L acid conj acid conj base

How are conjugate acid-base pairs related? By the transfer of a proton. (Look again at previous slide.)

Identify conjugate acid-base pairs: HCN(aq) + H 2 O(l) H 3 O + (aq) + CN − (aq) acid basec acidc base H 2 PO 4 − (aq) + OH − (aq)  HPO 4 2− (aq) + H 2 O(l) acid base c base c acid

Strong Acids & Bases A strong acid ionizes 100% in aq soln. eg. HCl(aq) + H 2 O(l)  H 3 O + (aq) + Cl − (aq) HClO 4 (aq) + H 2 O(l)  H 3 O + (aq) + ClO 4 − (aq) 100% rxn indicated by the “  ”

The “Big Seven” Strong Acids HCl(aq)hydrochloric acid HBr(aq)hydrobromic acid HI(aq)hydriodic acid HClO 4 (aq)perchloric acid HClO 3 (aq)chloric acid HNO 3 (aq)nitric acid 1 mol/L of these ↑ acids = 1 mol/L H 3 O + (aq) H 2 SO 4 (aq)sulfuric acid a diprotic acid  1 mol/L acid>1 mol/L H 3 O +

Review of Acid Nomenclature on the next three slides—taken from nomenclature powerpoint

How does the name of each acid correlate to ending of anion name? HCl(aq) Cl -, chloride hydrochloric acid H 2 SO 4 (aq) SO 4 2-, sulfate sulfuric acid HNO 2 (aq) NO 2 -, nitrite nitrous acid

Ending of anion name of acid determines name of acid 1. anion ends in “-ide” hydro_____ic acid [hydrobromic acid, HBr(aq), Br -, bromide] 2. anion ends in “-ate” _______ic acid [phosphoric acid, H 3 PO 4 (aq), PO 4 3-, phosphate] 3. anion ends in “ite” _______ous acid [nitrous acid, HNO 2 (aq), NO 2 -, nitrite ]

Examples of acids formulaname HClO 2 (aq)_______________ chlorous acid _______________ acetic (ethanoic) acid HC 2 H 3 O 2 (aq) H 3 PO 3 (aq)_______________ phosphorous acid _______________carbonic acid H 2 CO 3 (aq)

Strong Bases Strong Bases dissociate 100% in aq soln. Include the soluble ionic hydroxides of alkali metalsalkali earth metals LiOHSr(OH) 2 NaOHBa(OH) 2 KOHCa(OH) 2 low solubilityMg(OH) 2

These ionic hydroxides dissociate in water 100%: NaOH(s)  Na + (aq) + OH − (aq) Ba(OH) 2  Ba 2+ (aq) + 2OH − (aq)

Concentrated vs Dilute Acids/Bases Concentrated acids/bases: lots of mol/L eg H 2 SO 4 5 mol/L Dilute acids/bases: few mol/L, say 0.1 mol/L

Describe each of the following acids as strong/weak and dilute/conc mol/L HNO 3 (aq) a dilute, strong acid 2.5% (m/v) CH 3 COOH(aq) a dilute, weak acid mol/L H 2 SO 4 (aq) a concentrated, strong acid

Weak Acids and Bases Ionize less that 100%—usually much less—in aq solution. (eg acetic acid, CH3COOH) + H 2 OH 3 O + (aq) + CH 3 CO 2 − (aq) represents < 100% yield (an equilibrium)

Example of weak base, ammonia: NH 3 (aq) + H 2 O(l) NH 4 + (aq) + OH − (aq) ammonia ionizes only a few % what does this say about the yield of this rxn? (only a few %) Now indicate conj. acid-base pairs above.

NH 3 (aq) + H 2 O(l) NH 4 + (aq) + OH − (aq) wk base acid c. acid c. base

Homework 10.1LC # 1 – 12 RQ #