ACIDS, BASES & SALTS

NOTHING IN THE WORLD IS MORE DANGEROUS THAN SINCERE IGNORANCE AND CONSCIENTIOUS STUPIDITY. MARTIN LUTHER KING JR.

Ch.9 J.C. Rowe

Windsor University School of Medicine

What are Acids ?

An Acid is a substance which gives hydrogen ions when dissolved in water.

STRONG ACID is any acid that dissociates completely when it dissolves in water.

WEAK ACID is any acid that doesn’t dissociate completely when it dissolves in water.

Any compound that has a definite Ka (acidity constant) is a weak acid.

Strong Acids

The key point is that strong means 100% ionized. For some generic strong acid (with the generic formula HA) dissolved in water, we would write this equation:

HA(s) ---> H+(aq) + A¯

100% of the HA molecules dissociate in solution.

The [H+] of a strong acid is equal to the concentration of the acid

Strong Acids vs. Weak Acids

HCl Hydrochloric acid

H2SO4 Sulphuric acid

HNO3 Nitric acid HBr Hydrobromic

acid HI Hydroiodic acid

HF Hydrofluoric acid H2SO3 Sulphurous

acid H2O water HNO2 Nitrous acid H2CO3 Carbonic acid CH3COOH Acetic acid

Strong Acids Weak Acids

What are Bases ?

A base is a substance which reacts with an acid to give a salt & water only.

A base is a substance which accepts protons.

STRONG BASE is any metal hydroxide that dissociates completely when it dissolves in water.

In fact all ALKALI METAL HYDROXIDES are strong bases.

WEAK BASE is a base that is partially dissociated when dissolved in water.

Strong Bases

the key point is that strong means 100% ionized. For some generic strong base (with the generic formula BOH) dissolved in water, we would write this equation:

BOH(s) ---> B+(aq) + OH¯

100% of the BOH molecules dissociate in solution.

The [OH¯] of a strong base is equal to the concentration of the base.

Strong Bases vs. Weak Bases

NaOH Sodium hydro-xide

KOH Potassium hydro-xide

LiOH Lithium hydroxide

NH3 Ammonia CH3NH2

methylamine (CH3) 2NH

dimethyl-amine H2O water NH4OH

Ammonium hydroxide

Strong Bases

Weak Bases

Kw: The Water Ionization Constant

Kw = [H3O+] [OH¯] It can be determined by experiment and

has the value 1.011 x 10¯14 at 25 °C. Generally, a value of 1.00 x 10¯14 is

used. Hence, both [H3O+] and [OH¯] = 1.00 x

10¯7 M in pure water. This leads to several important results in the acid base world.

Result #1

The pH of pure water is 7

By definition, pH = -log [H3O+]

The pH of pure water then equals -log10-

7 , which is 7.

Result #2

If the pH or the pOH is known, the other can be found.

Take the negative logarithm of each side of the Kw equation as follows:

- log Kw = -log [H3O+] + -log [OH¯] -log 1.00 x 10¯14 = -log [H3O+] + -log [OH¯] Note the use of the add sign on the right side of

the equation. The result is usually written as: pKw = pH + pOH = 14 This is an extremely important equation.

Learn it well

Result #3

If the [H3O+] or the [OH¯] is known, the other can be found.

Simply divide Kw by the known value to get the other.

Suppose [H3O+] is known, then: [OH¯] = Kw / [H3O+] Suppose [OH¯] is known, then: [H3O+] = Kw / [OH¯]

Result #4

If one variable ( [H3O+] or [OH¯] ) changes value (either up or down), the other variable will change in the opposite direction.

The change in values will still preserve this fundamental equality:

Kw = [H3O+] [OH¯] Suppose [H3O+] became larger, therefore the [OH¯]

becomes smaller. Suppose [OH¯] became larger, therefore the [H3O+]

becomes smaller. This happens automatically and cannot be

stopped.

Acidity & pH

The pH of a solution is defined as the negative log(base 10) of the hydrogen ion (H +) molarity.

The pOH of a solution is defined as the negative log of the hydroxide ion (OH-) molarity.

At or around room temperature, the sum of the pH + the pOH is always

equal to 14.

Acidity & pH Cont’d.

pH = -log (H+) ; pOH = -log (OH-)

pH + pOH = 14

Molarity (M) is the # mole of solute in 1 liter of solution.

Solution is an homogeneous mixture

Solute is the part of a solution that gets dissolved into the solvent.

Solvent is the part of a solution into which the solute is dissolved.

pH of solutions Cont’d.

Pure water has a pH of 7. It is neutral. If you add an acid to water, the pH goes down.

The solution becomes acidic. If you add a base to pure water, the pH goes up.

The solution becomes basic. In a solution of a strong acid the hydrogen (H+)

ion concentration equals the concentration of the acid bcz the dissociation of the acid is complete.

In a solution of a strong base, the hydroxide (OH- ) ion concentration equals the concentration of the base.

pH of solutions : acidic, basic & neutral

Solution

pH Concentration of H+

Concentration of OH-

pOH

Acidic 1 10-1 M 10-13 M 13

Acidic 3 10-3 M 10-11 M 11

Acidic 5 10-5 M 10-9 M 9

Neutral ***

*** 7 ***

**10-7 M**

** 10-

7M****** 7

***

Basic 9 10-9 M 10-5 M 5

Basic 11 10-11 M 10-3 M 3

Basic 13 10-13 M 10-1 M 1

pH scale

The Observable Properties of Acids and Bases 1.

The word acid means "sour." All acids taste sour.

Well known from ancient times were vinegar, sour milk and lemon juice.

Aspirin (scientific name: acetylsalicylic acid) tastes sour if you don't swallow it fast enough.

All bases taste bitter. For example, mustard is a base. It tastes bitter.

Many medicines, because they are bases, taste bitter.

This is the reason cough syrups are advertised as having a "great grape taste." The taste is added in order to cover the bitterness of the active ingredient in cough syrup.

Acid Property #1 Base Property #1: 

The Observable Properties of Acids and Bases 2.

Acids make a blue vegetable dye called litmus turn red

Bases are substances which will restore the original blue color of litmus after having been reddened by an acid.

Acid Property #2 Base Property #2

The Observable Properties of Acids and Bases 3.

Acids destroy the chemical properties of bases

Bases destroy the chemical properties of acids

Acid Property #3:  Base Property #3

Neutralization is the name for this type of reaction

Acids conduct an electric current

Bases conduct an electric current.

Acid Property #4:  Base Property #4: 

This is a common property shared with salts. Acids, bases and salts are grouped together into a category called electrolytes, meaning that a water solution of the given substance will conduct an electric current.

Non-electrolyte solutions cannot conduct a current. The most common example of this is sugar dissolved in water.

The Observable Properties of Acids and Bases 4.

 The Observable Properties of Acids #5.

Upon chemically reacting with an active metal, acids will evolve hydrogen gas (H2). The key word, of course, is active.

Some metals, like gold, silver or platinium, are rather unreactive and it takes rather extreme conditions to get these "unreactive" metals to react.

Not so with the metals in this property. This include the alkali metals (Group I, Li to Rb), the alkaline earth metals (Group II, Be to Ra), as well as zinc and aluminum. Just bring the acid and the metal together at anything close to room temperature and you get a reaction.

Here's a sample reaction: Zn + 2 HCl(aq) ---> ZnCl2 + H2

Another common acid reaction some sources mention is that acids react with carbonates (and bicarbonates) to give carbon dioxide gas:

HCl + NaCO3 ---> CO2 + H2O + NaCl

The Observable Properties of Bases #5. 

Bases feel slippery, sometimes people say soapy. This is because they dissolve the fatty acids and oils from your skin and this cuts down on the friction between your fingers as you rub them together.

In essence, the base is making soap out of you. Yes, bases are involved in the production of soap!

In the early years of soap making, the soaps were very harsh on the skin and clothes due to the high base content.

1. Salts2. Monoatomic Ions3. Polyatomic Ions4. Classifications of Oxides

Salts & classifications of oxides

What are Salts?

Salts are the non-water product of an acid base neutralization.

There are four possible acid base reactions that produce salts. They are the reaction of a:

1) strong acid with a strong base.2) weak acid with a strong base.3) weak base with a strong acid.4) weak acid with a weak base.

Example reactions 1.

1) strong acid with a strong base

HCl + NaOH --> Na+ + Cl¯ + H2O

A salt of a strong acid and a strong base will produce a solution with pH = 7.

Example reactions 2.

2) weak acid with a strong baseHC2H3O2 + NaOH --> Na+ + C2H3O2¯ + H2O

A salt of a weak acid and a strong base will produce a solution with pH greater than 7. In other words, a salt of a weak acid produces a basic solution.

notice that the salts produced an opposite pH to its "parent.“

salt of a weak acid ---> greater than 7 (basic)

Leads to

Example reactions 3.

3) weak base with a strong acid.

NH3 + HCl --> NH4+ + Cl¯

A salt of a weak base and a strong acid will produce a solution with pH less than 7. In other words, a salt of a weak base produces an acidic solution

notice that the salts produced an opposite pH to its "parent.“

salt of a weak base ---> less than 7 (acidic)Leads to

Example reactions 4.

4) weak acid with a weak base

HC2H3O2 + NH3  --> NH4+ +

C2H3O2¯

A salt of a weak acid and a weak base produces a solution whose pH depends on the strengths of the acid and base which made the salt.

SALTS

When the hydrogen atom of an acid is replaced by a metal, the result is a salt.

Normal salt is the result of replacement of more than one hydrogen by a metal atom.

Acid salt is the result of replacement of only one of two hydrogen ions.

How to name a salt ?

The name of a salt has 2 parts: The 1rst is the name of the metal in the salt The 2nd comes from the name of the acid used. RULES:a. The name ends in –IDE- if the salt does not

have any oxygen in it.b. The name ends in –ATE- if the salt does have

oxygen in it.c. EXCEPTION: “sulphite” is an old-fashioned

name

Examples of naming

ACID FORMULA of ACID

EXAMPLE of SALT

NAME of SALT

Hydrochloric acid

HCl NaCl Sodium chloride

Nitric acid HNO3 NH4NO3 Ammonium nitrate

Sulphuric acid

H2SO4 Na2 SO4

CuSO4

NaHSO4 (an acid salt)

Sodium sulphateCopper (II) sulphateSodium hydrogensulphate

Carbonic acid

H2CO3 CaCO3

NaHCO3 (an acid salt)

Calcium carbonateSodium hydrogencarbonate

Properties of salts

Salts are ionic. They consist of cation & anion Some salts are soluble in water; others are not.

If the salt can be dissolve in water, the solution will conduct electricity. It is an electrolyte.

Salts have no color unless they contain a transition metal in either or both of its ions.

Precipitate is a solid deposit that forms when a substance comes out of a solution.

Solubility of some salts in waterSalt Solub

le

Partly soluble

Insoluble

Carbonate AmmoniumPotassiumSodium

------ All others

Clorides, Bromides,Iodides

All, except for

Lead in hot water

Lead, Silver

Hydrogencarbonates

All are soluble

------ ------

Hydroxides PotassiumSodium

BariumCalcium

All others

Nitrates All are soluble

-------- -------

Sulphates All except for CalciumSilver

BariumLead

Monoatomic ions

Polyatomic ions with a-2charge/Derivative

SO42- sulfate ion

SO32- sulfite ion

CO32- carbonate

ion

CrO42- chromate

ion Cr2O7

2- dichromate ion

HSO4- hydrogen

sulfate ion HSO3

- hydrogen sulfite ion

HCO3- hydrogen

carbo-nate ion

Polyatomic ions with a -3 charge/derivative

PO43- phosphate ion/ HPO4

2- hydrogen phosphate ion

PO33- phosphite ion/ H2PO4

- dihydrogen phosphate ion

There is only one polyatomic cation, NH4

+ = ammonium ion

How to classify oxides?

The oxides of non-metallic elements form acids with water.

Metal oxides are basic; they react with acids to give a salt & water only.

An acidic oxide reacts with water to produce an acidic solution.

A basic oxide reacts with water to produce an alkaline solution.

An amphoteric oxide(aluminium oxide) will react with both acids & bases

A neutral oxide(water, carbon monoxide) has no reaction with water.

Example is not the main thing in influencing others. It is the only thing. 

Albert Schweitzer