14. Acids & Bases chapter 10

Acids/Bases - by Physical Phenomena Method Acids Taste Feel Effect on metals Sour n/a Liberates H2 on reaction with iron, zinc & tin Bitter Slippery n/a Effect on indicators Litmus Phenolphthalein Red Colourless Blue Red

Lime(CaO) is the cheapest and most widely used commercial base (~18 billion kgs/yr in NA). Made by heating limestone (CaCO3) to drive off CO2 heat CaCO3 CaO + CO2 used for mortar and cement Also to 'sweeten' acidic(sour) soils. NB. Blue / pink lupins; 'natural' indicators for soil pH.

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

HCl H+ + Cl- CH3COOH H+ + CH3COO- H2O H+ + OH- 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 H+ + Cl- CH3COOH H+ + CH3COO- H2O H+ + 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 (+) H (-) .. .. .. .. . . . . . . . . . . . . . . . . H N H Cl H N H Cl .. .. .. .. H H Hydrogen Ammonia Ammonium chloride chloride Base + acid salt (+ water) Na OH + H Cl Na+Cl- + H2O sodium hydrogen sodium water hydroxide chloride chloride

Typical Inorganic Acids (mostly 'strong') Formula H3BO3 HIO3 HNO3 HClO4 H3PO4 H2SO4 HCl Name Boric Iodic Nitric Perchloric Phosphoric Sulfuric Hydrochloric Applications antiseptic, eye drops disinfectant fertilizers, explosives, dyes plating metals, explosives fertilizers, food additive fertilizers, paper, drugs cleaning metals/concrete 'weak' inorganic acids often end in '-ous', eg. nitrous-HNO2, sulfurous-H2SO3

Typical Organic Acids (usually 'weak') Formula HCOOH HOCOOH CH3COOH CH3CH2COOH CH3CH(OH)COOH HOC(CH2COOH)2- -COOH HO(CH2)3COOH Name formic carbonic acetic propionic lactic citric hydroxyBA benzoic Use bee/ant stings CO2 in H2O vinegar sweat, Sw. cheese muscle stress citrus fruit 'date rape' drug preservative -COOH

‘Foody’ Acids are Weak Fortunately!

Typical Bases Organic bases are the amines, R-N ie. carbon containing derivatives of ammonia, NH3 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(NaOH, Ca(OH)2) 2) ammonia (NH3) is weak 3) salts of strong bases & weak acids are 'weak', eg. sodium bicarbonate(NaHCO3), calcium carbonate(CaCO3)

Ammonia in water NH3 +H2O -> NH4 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 Base Salt HI + KOH KI + H2O hydrogen potassium iodide hydroxide iodide(Iodized salt) H2SO4 + Mg(OH)2 MgSO4 + 2H2O sulfuric magnesium magnesium acid hydroxide sulfate(Epsom salts) H2CO3 + Ca(OH)2 CaCO3 + 2H2O carbonic calcium calcium acid hydroxide carbonate(Tums) MSG = HOOC-CH2-CH2-CH(NH2)-COO- Na+

Water = Neutral (unless helped) H2O H+ + OH- Only 1 in 500 million! NB. [H+] = [OH-] .. .. + . . . . H . O . H + H+ H O H . . .. .. H hydronium ion 2H2O H3O+ + OH- hydronium ion

pH - the universal symbol for acidity pH, 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 pH of a solution is a measure of the acidity of that solution. pH = - log[H3O+] or [H+] pH = 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

pH of (neutral) Water Molarity (moles/L) of the proton(hydronium ion). [H3O+] or [H+] = 0.0000001M = 1 x 10-7 M (and [OH-] must also = 1 x 10-7M) If pH = - log[H3O+] Express conc'n. as power of 10 = - log(10-7) Use the exponent of 10 = -7 Reverse the sign = +7 Then the pH of neutral water is 7

The pH of an acidic solution is less than 7 The pH of a neutral solution equals 7 The pH of a basic solution is greater than 7 For every tenfold increase in the [H3O+] conc’n. there is a decrease of one unit in the pH For every tenfold decrease in the acidity there is an increase of one unit in the pH

Acidity and pH

Ex.1: The pH of 0.01 M HCl in water HCl H+ + Cl- 0.01M 0.01M 0.01M Since HCl is a strong acid, ie. completely ionized in water, the [H3O+] = 0.01 M = 1 x10-2M. Take the 'exponent' of 10, ie. -2, and reverse the sign, ie. 2. The pH of this solution must be 2.

Ex.2: The Basic Egg Fresh eggs have a [H30+] = 0.00000001 M. What is the pH of a fresh egg? Convert : [H+] = 10-8 M = [H3O+] Take the exponent of 10: -8 Reverse the sign: +8. A common pH for a fresh egg is 8.

Ex.3: How Acidic is a SopHt Drink? A typical pH of a soft drink is 3.0. What is the [H3O+] for a soft drink ? In this case we reverse the process. Since the pH is 3, the appropriate exponent of 10 must be the 'reverse' of +3, ie. -3. Hence the [H3O+] or [H+] must = 10-3M = 0.001 M for a 'soft' drink.

pH Material 1.0 - 3.0 Gastric juices(stomach) 2.2 - 2.4 Lemons 2.4 - 3.4 Vinegar 2.5 - 3.5 Soft drinks 3.0 - 3.4 Sour pickles 3.0 - 3.8 Wine 3.0 - 4.0 Oranges Acidic 4.0 - 4.4 Tomatoes 4.8 - 7.5 Human urine(usually 6.0) 5.6 Carbonated water, rain water 6.3 - 6.6 Cow’s milk 6.4 - 6.9 Human saliva (during rest) 6.6 - 7.6 Human milk 6.5 - 8.0 Drinking water

pH Material Neutral 7.0 Pure water 7.0 - 7.3 Human saliva(while eating) 7.3 - 7.5 Human blood 7.6 - 8.0 Fresh eggs 7.8 - 8.3 Seawater Basic 8.4 Sodium bicarbonate(saturated) 9.4 Calcium carbonate(saturated) 10.5 Milk of magnesia 10.5 - 11.9 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.

pHun with 'Bad Breath' H2CO3 CO2 + H2O If CO2 is blown into water, equilibrium shifts left  [H2CO3] increases  acidity increases But add citric acid to HCO3- from Alka Seltzer H2CO3 HCO3- + H+ bicarbonate More H+ means more H2CO3 which (According to Le Chatelier’s P.) produces more CO2 which escapes as bubbles( and the customer is happy).

Escaping CO2 gives your (leavened)Bread a Lift !

pH of Blood( must be kept constant!) H2CO3 + H2O H3O+ + HCO3- If pH drops, eg. during illness, the [H3O+] begins to increase but will react with HCO3- to form H2CO3, ie. CO2, which is exhaled. Or the reverse if pH of blood drops. [H2CO3] is maintained by exhaling / inhaling CO2. Keep your lungs in good working order! What happens to blood pH when hyperventilating?

LeChatelier’s Principle H2O + CO2 -> H2CO3 If more CO2 is produced (ie hyperventilation) , then body reacts to produce more H2CO3 to offset the change and the pH drops.

Buffers in Blood Keep pH near 7.40 If pH drops below 7.35, called “acidosis” pH below 7.0 or above 7.8 can cause death Buffer contains a weak acid (H2CO3) and the salt of a weak acid and a strong base ie NaHCO3.

Effects of added acid and base to a buffer Added base reacts with the weak acid to neutralize it Added acid reacts with HCO3- to produce H2CO3.

Some Common Antacids Name Formula Product 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 Mg(OH)2 CaCO3 NaHCO3 Al(OH)3 MgCO3 NaAI(OH)2CO3 Milk of magnesia Tums, Di-Gel AlkaSeltzer, 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 CaCO3 let's try a stronger base Mg(OH)2 + 2HCl MgCl2 + 2H2O OOPS, it's a laxative! Right idea, try again with even more OHs Al(OH)3 + 3HCl AlCl3 + 3H2O DAMN, this time it constipates! Why not combine them!? But it will never sell as: Magnesium Aluminum Hydroxide

How about? MgAlox No, too 'nerdy', but-