14. Acids & Bases

chapter 10

Acids/Bases - by Physical Phenomena

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

Blue

Red

Method Acids Bases

Red

Colourless

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.

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

Acids/Bases - by Chemical Structure

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

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.

CH3COOH H+ + CH3COO-

H2O H+ + OH-

HCl H+ + Cl-

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.

N..

..

..

..

....

......H . .. ... .. H

H

HH

H

HH

Cl N Cl.. .. ..

Base + acid salt (+ water)

Ammonia Hydrogenchloride

Ammonium chloride

Na OH + H Cl Na+Cl- + H2O

hydrogenchloride

sodiumhydroxide

watersodiumchloride

(+) (-)

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-COOH

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

‘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

HI + KOH KI + H2O hydrogeniodide

potassiumhydroxide

potassium iodide(Iodized salt)

Acid Base Salt

H2SO4 + Mg(OH)2 MgSO4 + 2H2O sulfuricacid

magnesiumsulfate(Epsom salts)hydroxide

magnesium

H2CO3 + Ca(OH)2 CaCO3 + 2H2O carbonic

acidcalcium

carbonate(Tums)hydroxidecalcium

MSG = HOOC-CH2-CH2-CH(NH2)-COO- Na+

H2O H+ + OH-

OHH

HH+H..

..

..

..... ... .+ O. H

+

hydronium ion

2H2O H3O+ + OH-

hydronium ion

Water = Neutral (unless helped)

Only 1 in 500 million! NB. [H+] = [OH-]

pH, the symbol for acidity, represents the

'power of the Hydrogen (or Hydronium) ion'.

pH - the universal symbol for acidity

The letter 'p' begins the English word power, the French word puissance, the German word potenz.

pH = - log[H3O+] or [H+]

The pH of a solution is a measure of the acidity of that solution.

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

[H3O+] or [H+] = 0.0000001M = 1 x 10-7 M

Molarity (moles/L) of the proton(hydronium ion).

(and [OH-] must also = 1 x 10-7M)

Express conc'n. as power of 10 = - log(10-7)

If pH = - log[H3O+]

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 pHpH [H3O

+]

Strongly acidic 1 10-1 0.1 2 10-2 0.01 3 10-3 0.001 4 10-4 0.0001 5 10-5 0.00001

Weakly acidic 6 10-6 0.000001Neutral 7 10-7 0.0000001(at 25oC)Weakly basic 8 10-8 0.00000001

9 10-9 0.000000001 10 10-10 0.0000000001 11 10-11 0.00000000001 12 10-12 0.000000000001 13 10-13 0.0000000000001

Strongly basic 14 10-14 0.00000000000001

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

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.

Fresh eggs have a [H30+] = 0.00000001 M.

What is the pH of a fresh egg?

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.

1.0 - 3.02.2 - 2.42.4 - 3.42.5 - 3.53.0 - 3.4

6.6 - 7.66.5 - 8.0

3.0 - 3.83.0 - 4.04.0 - 4.44.8 - 7.5

6.4 - 6.9

5.66.3 - 6.6

Gastric juices(stomach)LemonsVinegarSoft drinksSour picklesWineOrangesTomatoesHuman urine(usually 6.0)Carbonated water, rain waterCow’s milkHuman saliva (during rest)Human milkDrinking water

pH Material

Acidic

7.0 - 7.3

7.3 - 7.5

7.6 - 8.0

7.8 - 8.3

8.4

7.0

9.4

10.5

10.5 - 11.9

Human saliva(while eating)

Human blood

Fresh eggsSeawater

Sodium bicarbonate(saturated)

Calcium carbonate(saturated)

Milk of magnesia

Household ammonia

Pure water

pH Material

Neutral

Basic

when a stress is placed on a system in equilibrium, the system tends to change in a

way that relieves the stress.

Le Chatelier’s Principle states that:

pHun with 'Bad Breath'

H2CO3 CO2 + H2O

If CO2 is blown into water, equilibrium shifts left

[H2CO3] increases acidity increases

H2CO3 HCO3- + H+

But add citric acid to HCO3- from Alka Seltzer

More H+ means more H2CO3 which (According to Le Chatelier’s P.) produces more CO2 which escapes as bubbles( and the customer is happy).

bicarbonate

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

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

Build a 'Better' Antacid, and the World….

How about? MgAlox No, too 'nerdy',

but-