14 Acids Bases chapter 10 Acids Bases

14. Acids & Bases chapter 10

Acids/Bases - by Physical Phenomena Method Acids Bases Taste Sour Bitter Feel n/a Slippery Effect on metals Liberates H 2 on reaction with iron, zinc & tin n/a Effect on indicators Litmus Phenolphthalein Red Blue Colourless Red

Lime(Ca. O) is the cheapest and most widely used commercial base (~18 billion kgs/yr in NA). Made by heating limestone (Ca. CO 3) to drive off CO 2 heat Ca. CO 3 Ca. O + CO 2 used for mortar and cement Also to 'sweeten' acidic(sour) soils. NB. Blue / pink lupins; 'natural' indicators for soil p. H.

Acids/Bases - by Chemical Structure Definition Acids Bases 1) Arrhenius Generates H+ in water Generates OHin water 2) Bronsted -Lowry Transfers H+ to a base Accepts H+ from an acid electron acceptor electron donor 3) Lewis NB: H+ = proton OH- = hydroxide ion

Bronsted -Lowry definition: an acid is any substance that can transfer a proton to another substance a base is a substance that can accept a proton

A strong acid ionizes completely and irreversibly in water, often 'inorganic', eg. hydrochloric acid. A weak acid ionizes reversibly and therefore only partially, often 'organic', eg. acetic acid. HCl CH 3 COOH H 2 O H+ + Cl- H+ + CH 3 COOH+ + OH-

In neutralization an acid and a base react to produce a solution that’s neither acidic nor basic. A salt is a compound (other than water ) produced by the reaction of an acid with a base.

H. . . N. H. . H Ammonia Base . . H. Cl. . . Hydrogen chloride + Na OH + sodium hydroxide (+) H. . (-). . . N H. Cl. . . H Ammonium chloride acid salt (+ water) H Cl hydrogen chloride Na +Cl- + H 2 O sodium water chloride

Typical Inorganic Acids (mostly 'strong') Formula H 3 BO 3 HIO 3 HNO 3 HCl. O 4 H 3 PO 4 H 2 SO 4 HCl Name Applications Bor antiseptic ic Iodic , eye drops disinfectant Nitric fertilizers, explosives, dyes Perchloric plating metals, explosives Phosphoric fertilizers, food additive Sulfuric fertilizers, paper, drugs Hydrochloric cleaning metals/concrete 'weak' inorganic acids often end in '-ous', eg. nitrous-HNO 2, sulfurous-H 2 SO 3

Typical Organic Acids (usually 'weak') Formula HCOOH HOCOOH CH 3 CH 2 COOH CH 3 CH(OH)COOH HOC(CH 2 COOH)2 -COOH HO(CH 2)3 COOH -COOH Name form ic carbonic acetic propionic lactic citric hydroxy. BA ben zoic Use be e/ant stings CO 2 in H 2 O vinegar sweat, Sw. cheese muscle stress cit rus fruit 'date rape' drug pres ervative

‘Foody’ Acids are Weak Fortunately!

Typical Bases Organic bases are the amines, R-N ie. carbon containing derivatives of ammonia, NH 3 Inorganic bases can be 'strong' or 'weak', eg. 1) the 'hydroxide' derivatives of the alkali & alkaline earth elements, ie. rows 1, 2 (3) of periodic table, are always strong eg. sodium / calcium hydroxide(Na. OH, Ca(OH)2) 2) ammonia (NH 3) is weak 3) salts of strong bases & weak acids are 'weak', eg. sodium bicarbonate(Na. HCO 3), calcium carbonate(Ca. CO 3)

Ammonia in water • NH 3 +H 2 O -> NH 4 OH (ammonium hydroxide) • A source of OH-, hence a base • But a weak base since only partially dissociated (about 1%)

Lots of Strong Bases around the House !

Typical Salts Acid HI + hydrogen iodide Base KOH potassium hydroxide Salt KI + H 2 O potassium iodide(Iodized salt) H 2 SO 4 + sulfuric acid Mg(OH)2 magnesium hydroxide Mg. SO 4 + 2 H 2 O magnesium sulfate(Epsom salts) Ca(OH)2 calcium hydroxide Ca. CO 3 + 2 H 2 O calcium carbonate(Tums) H 2 CO 3 carbonic acid + MSG = HOOC-CH 2 -CH(NH 2)-COO- Na+

Water = Neutral (unless helped) H 2 O H+ + OH- Only 1 in 500 million! NB. [H+] = [OH-] . . . H. O H. . + +. . H. O. H. . H+ H hydronium ion 2 H 2 O H 3 O + hydronium ion + OH-

p. H - the universal symbol for acidity p. H, the symbol for acidity, represents the 'power of the Hydrogen (or Hydronium) ion'. The letter 'p' begins the English word power, the French word puissance, the German word potenz.

The p. H of a solution is a measure of the acidity of that solution. p. H = - log[H 3 O+] or [H+] p. H = the negative logarithm of the proton (hydronium ion) concentration(= [ x ] ) (as Molarity = moles/Liter). Don't panic! write the [H+] as a power of 10 use the exponent of 10 reverse its sign

p. H of (neutral) Water Molarity (moles/L) of the proton(hydronium ion). [H 3 O+] or [H+] = 0. 0000001 M = 1 x 10 -7 M (and [OH-] must also = 1 x 10 -7 M) If p. H = - log[H 3 O+] Express conc'n. as power of 10 = - log(10 -7) Use the exponent of 10 = -7 Reverse the sign = +7 Then the p. H of neutral water is 7

The p. H of an acidic solution is less than 7 The p. H of a neutral solution equals 7 The p. H of a basic solution is greater than 7 For every tenfold increase in the [H 3 O+] conc’n. there is a decrease of one unit in the p. H For every tenfold decrease in the acidity there is an increase of one unit in the p. H

Acidity and p. H

Ex. 1: The p. H of 0. 01 M HCl in water HCl 0. 01 M H+ 0. 01 M + Cl 0. 01 M Since HCl is a strong acid, ie. completely ionized in water, the [H 3 O+] = 0. 01 M = 1 x 10 -2 M. Tak e the 'exponent' of 10, ie. -2, and reverse the sign, ie. 2. The p. H of this solution must be 2.

Ex. 2: The Basic Egg Fresh eggs have a [H 30+] = 0. 00000001 M. What is the p. H of a fresh egg? Convert : [H+] = 10 -8 M = [H 3 O+] Take the exponent of 10: -8 Reverse the sign: +8. A common p. H for a fresh egg is 8.

Ex. 3: How Acidic is a Sop. Ht Drink? A typical p. H of a soft drink is 3. 0. What is the [H 3 O+] for a soft drink ? In this case we reverse the process. Since the p. H is 3, the appropriate exponent of 10 must be the 'reverse' of +3, ie. -3. Henc e the [H 3 O+] or [H+] must = 10 -3 M = 0. 001 M for a 'soft' drink.

p. H Acidic 1. 0 - 3. 0 2. 2 - 2. 4 - 3. 4 2. 5 - 3. 5 3. 0 - 3. 4 3. 0 - 3. 8 3. 0 - 4. 4 4. 8 - 7. 5 5. 6 6. 3 - 6. 6 6. 4 - 6. 9 6. 6 - 7. 6 6. 5 - 8. 0 Material Gastric juices(stomach) Lemons Vinegar Soft drinks Sour pickles Wine Oranges Tomatoes Human urine(usually 6. 0) Carbonated water, rain water Cow’s milk Human saliva (during rest) Human milk Drinking water

p. H Neutral 7. 0 - 7. 3 - 7. 5 7. 6 - 8. 0 7. 8 - 8. 3 Basic 8. 4 9. 4 10. 5 - 11. 9 Material Pure water Human saliva(while eating) Human blood Fresh eggs Seawater Sodium bicarbonate(saturated) Calcium carbonate(saturated) Milk of magnesia Household ammonia

Le Chatelier’s Principle states that: when a stress is placed on a system in equilibrium, the system tends to change in a way that relieves the stress.

p. Hun with 'Bad Breath' H 2 CO 3 CO 2 + H 2 O If CO 2 is blown into water, equilibrium shifts left [H 2 CO 3] increases acidity increases But add citric acid to HCO 3 - from Alka Seltzer H 2 CO 3 HCO 3+ H+ bicarbonate More H+ means more H 2 CO 3 which (According to Le Chatelier’s P. ) produces more CO 2 which escapes as bubbles( and the customer is happy).

Escaping CO 2 gives your (leavened)Bread a Lift !

p. H of Blood( must be kept constant!) H 2 CO 3 + H 2 O H 3 O+ + HCO 3 - If p. H drops, eg. during illness, the [H 3 O+] begins to increase but will react with HCO 3 - to form H 2 CO 3, ie. CO 2, which is exhaled. Or the reverse if p. H of blood drops. [H 2 CO 3] is maintained by exhaling / inhaling CO 2. Keep your lungs in good working order! What happens to blood p. H when hyperventilating?

Le. Chatelier’s Principle • H 2 O + CO 2 -> H 2 CO 3 • If more CO 2 is produced (ie hyperventilation) , then body reacts to produce more H 2 CO 3 to offset the change and the p. H drops.

Buffers in Blood • • Keep p. H near 7. 40 If p. H drops below 7. 35, called “acidosis” p. H below 7. 0 or above 7. 8 can cause death Buffer contains a weak acid (H 2 CO 3) and the salt of a weak acid and a strong base ie Na. HCO 3.

Effects of added acid and base to a buffer • Added base reacts with the weak acid to neutralize it • Added acid reacts with HCO 3 - to produce H 2 CO 3.

Some Common Antacids Name 1) Magnesium hydroxide 2) Calcium carbonate 3) Sodium carbonate 4) Aluminum hydroxide 5) I + 4 6) 1 + 4 & magnesium carbonate 7) Dihydroxyaluminum sodium carbonate 8)1 + 2 Formula Product Mg(OH)2 Ca. CO 3 Na. HCO 3 Al(OH)3 Mg. C O 3 Na. AI(OH)2 C O 3 Milk of magnesia Tums, Di-Gel Alka. Seltzer, soda Amphojel Maalox, Mylanta Di-Gel liquid Rolaids " sodium-free Antacids, for 'heartburn', = ~$1 billion(US)/yr in NA

Ah… Relief = Neutralization

Build a 'Better' Antacid, and the World…. Instead of Ca. CO 3 let's try a stronger base Mg(OH)2 + 2 HCl Mg. Cl 2 + 2 H 2 O OOPS, it's a laxative! Right idea, try again with even more OHs Al(OH)3 + 3 HCl Al. Cl 3 + 3 H 2 O DAMN, this time it constipates! Why not combine them!? But it will never sell as: Magnesium Aluminum Hydroxide

How about? Mg. Alox No, too 'nerdy', but-