1. How does pH value affect our environment?
Acids & bases
How does pH value affect our environment?

2. Recall Questions What is an acid? What is a base/alkali?
A substance which produces hydrogen ions (protons)
when dissolves in water.
A base refers to substances like metal oxides and metal
hydroxides.
A substance which reacts with acid to form salt and water only
An alkali is a soluble base which in solution produces hydroxide
ions.
Most bases are insoluble in water. 3 soluble bases are
NaO/NaOH,KO/KOH,CaO/Ca(OH)2

3. Recall Questions What causes acidity?
It is the hydrogen ions that give an acid its acidic properties
when they dissolve in water and dissociate into ions.
E.g. HCl gas is a covalent compound. When dissolves in water,
it forms HCl acid which dissolciate to form ions.

4. Recall Questions What is basicity(proticity)? Basicity
refers to the no.of H atoms in one molecule of acid that acn be
repleced by a metal.
refers to the no. of H+ that can be replaced by one molecule
of that acid.
E.g. HCl (monobasic),H2SO4(dibasci),H3PO4(tribasic)

5. Bronsted-Lowry theory
An acid is defined as a molecule or ion that acts as a proton donor (H+). A base is defned as a molecule or ion that acts as a proton acceptor (H+).
On the left, HCl acts as an acid because it donates H+ to the water molecule, which acts as a base since it accepts the H+ to form the hydronium ion (H3O+)
On the right, the hydronium ion (H3O+) acts as an acid by donating the H+ to the Cl- to form HCl . Cl- acts as a base.
HCl(g) + H2O(l) H3O+(aq) + Cl-(aq)

6. Hydrogen chloride gas dissolved in water
HCl(g) + H2O(l) H3O+(aq) + Cl-(aq)
The equation can be split into
(i) HCl(aq) Cl-(aq) H+(aq)
acid conjugate base
(ii) H2O(l) + H+(aq) H3O+(aq)
base conjugate acid
This reaction shows that when a species loses a proton, the product is a base since the process is reversible ( to some degree depending on the acid ) The chloride ion is the conjugate base of the hydrogen chloride molecule.
This reaction shows that when a species gains a proton the product has to be an acid since the process is reversible. The hydronium ion is the conjugate acid of the water molecule.

7. Ammonia gas dissolved in water
NH3(g) + H2O(l) NH4+(aq) + OH-(aq)
Ammonia acts as a base by accepting a proton from water. Water acts as an acid.
Species that are able to act as both acids and bases (H+ donor or acceptor), depending on the species they are reacting are termed amhiprotic.
What does ammonia and water act as
in the reaction above?

8. Competition between acid/base and its conjugate
(i) HCl(g) H2O(l) H3O+(aq) Cl-(aq)
acid base conjugate acid conjugate base
(ii) CH3COOH(l) + H2O(l) H3O+ (aq) + CH3OOO-(aq)
acid base conjugate acid conjugate base
Water is a much stronger base than chloride ion and has a stronger tendency to accept proton.The equilibrium shifts more to the right.
Ethanote ion is a much stronger base than water molecule. The equilbrium shifts to the left.

9. Gas-phase acid-base reaction
HCl(g) NH3(g) NH4Cl(s)
The Bonsted-Lowry model can be extended to gas- phase acid-base reaction.
It involves the transfer
of hydrogen ion from
hydrogen chloride to
ammonia.

10. (i) HCl(g) + H2O(l) H3O+(aq) + Cl-(aq)
acid base conjugate acid conjugate base
(ii) CH3COOH(l) + H2O(l) H3O+ (aq) + CH3OOO-(aq)
acid base conjugate acid conjugate base
Strong acids produce relatively weak conjugate bases in aqueous solutions.
Weak acids produce relatvely strong conjugate acids in aqueous solutions.

11. Common acids & conjugate bases in order of strengths

12. Acids that have single proton to donate – monoprotic (monobasic).
E.g. HCl(aq), HNO3(aq), HNO2(aq)
Acids that have 2 protons to donate – diprotic
E.g. H2SO4(aq), H2SO3(aq), H2CO3(aq)
H3PO4(aq) is triprotic.

13. Lewis theory
A Lewis acid is defined as a substance that can accept a pair of electrons from another atom to form a dative (coordinate) covalent bond.
A Lewis base is defined as a substance that can donate a pair of electrons to another atom to form a dative (coordinate) covalent bond.
B represents a base (with 1 or more pair of electrons)
H+ represents the proton
BH+ represents the conjugate acid
B: H+  +BH

14. Examples Reaction between ammonia and proton H3N: H+  +NH4
Reaction between a water molecule and proton
H2O: H+  H3O+
This reaction shows that when a species loses a proton, the product is a base since the process is reversible ( to some degree depending on the acid ) The chloride ion is the conjugate base of the hydrogen chloride molecule.
This reaction shows that when a species gains a proton the product has to be an acid since the process is reversible. The hydronium ion is the conjugate acid of the water molecule.

15. Lewis bonding
In complex ions formed by transition metals The 6 water molecules, each donate a lone air electrons from oxygen of their water molecules to the empty 3d orbitals of iron.
Water molecules act as Lewis base (electron donors)
Fe(III) ion acts as Lewis acid (electrton pair acceptor)
What does each water molecule and iron(III) ion act as in the reaction above?

16. Properties of acids and bases
Construct a concept map to show the physical and chemical properties of acids and bases

17. Preparation of Salts
Construct a concept map to show a summary of the preparation of salts.

18. Strong and weak acids and bases
Strong acid
When strong acid dissolves, virtually all acid molecules react with the water to produce hydronium ions In general for a strong acid HA
HCl-(g) + H2O(l) -> H3O+(aq) + Cl-(aq)
HNO3(l) + H2O(l) -> H3O+(aq) + NO3-(aq)
H2SO4(l) + H2O(l) -> H3O+(aq) + HSO4-(aq)
HClO4(l) + H2O(l) -> H3O+(aq) + ClO4-(aq) chloric(VII) (perchloric)
A strong acid is one which undergoes complete ionisation in aqeuous solution, forming more H+.
HA + H2O(l)  H3O+(aq) + A-(aq) or HA  H+(aq) + A-(aq)
0% % % %
Examples : HCl, H2SO4,HNO3, HClO4

19. Strong and weak acids and bases
When a weak acid dissolves in water, only a small % of its molecules (typically 1%) react with water molecules to release hydrogen or hydronium ions. The equilibrium lies on the left- hand side of the equation.
CH3COOH(l) + H2O(l) -><- CH3COO- (aq)+ H3O+(aq)
CO2(g) + 2H2O(l) -><- HCO3-(aq) + H3O+(aq)
A weak acid is one which undergoes slight or partial ionisation in aqeuous solution forming fewer H+ ions. Most of the acid remain as undissociated molecules.
HA + H2O(l) H3O+(aq) + A-(aq) or HA H+(aq) + A-(aq)
99% % % 1%
Examples : CH3COOH, aqueous carbon dioxide

20. Distinguish between strong and weak acids
0.1 mol dm-3 HCl(aq)
0.1 mol dm-3 CH3COOH (aq)
[H+(aq)]
0.1 mol dm-3
mol dm-3 pH
1.00
2.87
Electrical conductivity
high
low
Relative rate of reaction with magnesium
fast
slow
Relative rate of reaction with calcium carbonate
Base on the information above, how do we distinguish betwee strong and weak acids of the same concentration (e.g. HCl and CH3COOH)?

21. How to distinguish between strong and weak acids?
A weak acid has a lower concentration of hydrogen ions and hence a higher pH than a stronger acid of the same concentration.
A weak acid, because of its lower concentration of hydrogen ions, will have much poorer electrical conductor than a stronger acid of the same concentration.
Weak acids react more slowly with reactive metals, metal oxides, metal carbonates and metal hydrogencarbonates than strong acids of the same concentration.
Strong and weak acids can also be distnguished by measuring and comparing their enthalpies of meutralisation.
(i) This can be established usin narrow range universal indicator paper or a pH probe and meter.
(iii)Due to a lower conc of H+ in the weak acid since it is the H+ that are responsible for the typical chemical properties of acids.
Concentrated applied to acid means relatively large amt of the pure acid (weak or strong) has been dissolved in a relatively small vol of water. [Conc of acid can be increased or decreased by adjusting the vol of water]
Therefore, a 0.1 moldm-3 soln of HCl can be described as a dilute solution of a strong acid or 0.1 mol dm-3 soln of CH3COOH can be described as a dilute solution of a weak acid.
A concentrated soln of a weak acid might contain a greater conc of H+ than a very dilute soln of a strong acid.
The strength of an acid refers to teh extent to which the acid molecule dissociate into ions when dissolve in water.
Acids can be strong or weak depending on the degree of iocnisation.
Acid strength does not change as the acid is diluted (at a constant temp).
What is the difference between the strength (strong and weak)
and the concentrated (concentrated or dilute)?

22. Strong and weak acids and bases
Strong base
A strong base undergoes almost 100% dissociation/ionisation when in dilute aqueous solution.
BOH B+(aq) + OH-(aq)
0% %
HCl-(g) + H2O(l) -> H3O+(aq) + Cl-(aq)
HNO3(l) + H2O(l) -> H3O+(aq) + NO3-(aq)
H2SO4(l) + H2O(l) -> H3O+(aq) + HSO4-(aq)
HClO4(l) + H2O(l) -> H3O+(aq) + ClO4-(aq) chloric(VII) (perchloric)
Examples : NaOH, KOH, Ba(OH)2

23. Strong and weak acids and bases
Weak base
All bases are weak except the hydroxides of groups 1 and 2.
Weak bases are composed of molecules that react with water molecules to release hydoxide ions. In general for a weak molecular base, BOH
The equiibrium lies on the left side of the equation.
BOH + (aq) B+(aq) + OH-(aq)
NH3(g) + (aq) -><- NH4+(aq) + OH-(aq)
C2H5NH2(g) + (aq) -><- C2H5NH3+(aq) + OH-(aq)
Note: Ca(OH)2 is a strong base but it is very dilute because it is only slightly soluble in water
Ca(OH)2(s) + (aq) -> Ca2+(aq) + 2OH-(aq)
Examples : aqueous ammonia, ethylamine, caffeine, bases
of nuclei acids

24. The pH indicator
scale that measures the strength of an acid and alkali.
pH of a substance is measured when it is dissolved in water.
pH stands for “power of hydrogen”
[H+] = 1 x 10-n moldm-3 ( n = pH number)
The pH scale is logarithmic to the base 10 Eery change in 1 unit on the pH scale means a change in H+ conc of 10 units.
E.g. Solun with pH 4 is 10 times more acidic than an aqueous soln with a pH of 5 and 100 times more acidic than an aqueous soln with pH of 6
A pH probe works something like a little battery powered by the test solution. In a neutral solution the pH probe would generate 0v. An acidic sample would generate a positive voltage proportional to the ionic strength of the sample being measuring. A basic solution does the same except resulting in a negative voltage output.

25. The pH Scale
The pH scale is logarithmic to the base 10 Eery change in 1 unit on the pH scale means a change in H+ conc of 10 units.
E.g. Solun with pH 4 is 10 times more acidic than an aqueous soln with a pH of 5 and 100 times more acidic than an aqueous soln with pH of 6
A pH probe works something like a little battery powered by the test solution. In a neutral solution the pH probe would generate 0v. An acidic sample would generate a positive voltage proportional to the ionic strength of the sample being measuring. A basic solution does the same except resulting in a negative voltage output.

26. pH probe and meter
An accurate method of measuring pH value. A pH probe is dipped into the solution being tested and the pH value is then read directly from the meter.
So, a standard pH Probe generates a voltage either positive or negative proportional to the acidity or alkalinity (baseness) of whatever its testing.