ACIDS, BASES & SALTS NOTHING IN THE WORLD IS MORE DANGEROUS THAN SINCERE IGNORANCE AND CONSCIENTIOUS...
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Transcript of ACIDS, BASES & SALTS NOTHING IN THE WORLD IS MORE DANGEROUS THAN SINCERE IGNORANCE AND CONSCIENTIOUS...
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