1. Chapter 6
Acids and Bases

2. Section 6.1 –Theories of Acids and Bases
Acids are used for a variety of things including food preservatives, batteries, cleaning products and treatment of accidental chemical spills.

3. Properties of Acids and Bases
Test
Acids
Bases
Litmus Paper
Turns Blue litmus paper Red
Turns Red litmus paper Blue
pH paper
pH < 7
pH > 7
Conductivity in Solution
Electrolyte
Reaction with active metals such as Zn, Mg
Reacts to produce
H2 (g)
Does not react to produce H2 (g)
Taste
Sour
Bitter
Feel
N/A
slippery

4. Explaining the Properties of Acids and Bases:
Svante August Arrhenius ( ) theorized that certain substances break apart in water to form ions, producing solutions that can then conduct electric current. Knowing that both acidic and basic solutions conduct electric current led to his theory on acids and bases.

5. The Arrhenius Theory of Acids and Bases
An Arrhenius acid is a substance that ionizes to form hydrogen ions, H+(aq),­ in aqueous solution.
An Arrhenius base is a substance that dissociates to produce hydroxide ions, OH-(aq), in aqueous solution.
HCl(aq) in water H+(aq) + Cl-(aq)
NaOH(s) in water Na+(aq) + OH-(aq)

6. Ionize: Acidic molecular substances dissolve in water forming ions.
Dissociate: When ionic substances dissolve in water and break apart into ions. They do not ionize because they are already made of ions.

7. A Limitation of the Arrhenius Theory
By Arrhenius’ definition, a base must contain OH-(aq) ions that are released during dissociation. However some substances like NH3(aq) and NaHCO3(aq) are basic but do not contain OH-(aq). We would not be able to predict that these compounds are basic in aqueous solution using Arrhenius’ definition.

8. Arrhenius’ theory needs to be modified slightly
A base dissociates or reacts with water to produce OH-(aq) ions in aqueous solution.
Ammonia reacts with water to produce OH- ions
NH3 (g) + H2O(l) NH4+(aq) + OH-(aq)

9. According to Arrhenius, acids ionize in solution, forming H+(aq) ions
According to Arrhenius, acids ionize in solution, forming H+(aq) ions. However, analytical technology developed in the twentieth century has allow scientists to gather evidence that H+ ions produced by the ionization of an acid do not exist in isolation. Instead they exist as H3O+(aq) ions. Since water is a polar molecule, having a partially negative charge on the oxygen, it interacts with the positively charged H+ ion.
Arrhenius’ theory again needs to be modified slightly.
An acid reacts with water to produce H3O+(aq) ions in aqueous solution.

10. Arrhenius Theory
HCl(g) + H2O(aq) H+(aq) + Cl-(aq) + H2O(aq)
Modified Arrhenius Theory
HCl(g) + H2O(aq) H3O +(aq) + Cl-(aq)

12. Practise Problems
Naming Acid worksheet
Pg. 209 # 1-2

14. Arrhenius Theory of Acids and Bases
An Arrhenius acid is a substance that ionizes to form hydrogen ions in aqueous solution
Ex. HCl(aq) - H+(aq) + Cl-(aq)
An Arrhenius base is a substance that dissociates to produce hydroxide ions in aqueous solution
Ex. NaOH - Na+(aq) + OH-(aq)

15. Modifications to the theory
Bases
What about NH3(aq) and NaHCO3(aq) ?
We would not be able to predict that these compounds are basic in aqueous solution using Arrhenius’ definition.
Modificaation
A base dissociates or reacts with water to produce OH-(aq) ions in aqueous solution.
Ex. NH3(aq) reacts with water to produce OH- ions
NH3 (g) + H2O(l)  NH4+(aq) + OH-(aq)

16. Modifications Continued
Acids
Advanced technology has allowed scientists to gather evidence that H+ ions produced by the ionization of an acid do not exist in isolation.
Instead they exist as H3O+(aq) ions
This is a result of the polarity of water
partially negative charge on the oxygen, interacts with the positively charged H+ ion.
Modification
An acid reacts with water to produce H3O+(aq) ions in aqueous solution.

17. Modified Arrhenius Theory
HCl(g) + H2O(aq) --H+(aq) + Cl-(aq) + H2O(aq)
Modified Arrhenius Theory
HCl(g) + H2O(aq) H3O +(aq) + Cl-(aq)

18. Oxides
Non-metallic oxides (substances made from a non-metal and oxygen) undergo a two-step reaction in water to form acids.
Step 1: CO2(g) + H2O(l) H2CO3(aq) 
Step 2: H2CO3(aq) + H2O(l) H3O+(aq) + HCO3-(aq)
or 
Step 1: SO2(g) + H2O(l) H2SO3(aq) 
Step 2: H2SO3(aq) + H2O(l) H3O+(aq) + HSO3-(aq)

19. Metallic oxides
Metallic oxides (substances made from a metal and oxygen) undergo a two-step reaction in water to form bases.
Step 1: Na2O(s) + H2O(l) NaOH(aq)
Step 2: 2NaOH(aq) in water 2Na+(aq) + 2OH-(aq)
Note: Step 1 is a reaction with water, while step 2 is a dissociation in water. 
Step 1: BaO(s) + H2O(l) Ba(OH)2(aq)
Step 2: Ba(OH)2(aq) in water Ba2+(aq) + 2OH-(aq)

20. Practice
Do Section 6.1 Review P.217

21. Strong and Weak Acids
Different acids with the same concentration can have different acidic properties.
Ex mol/L of Sulfuric acid vs. vinegar
Different bases with the same concentration can have different basic properties.
This is because different acids and bases ionize in solution to different degrees.

22. Strong Acids
An acid that ionizes nearly 100% in water is called a strong acid.
Ex. Hydrochloric acid is a strong acid.
HCl(g) + H2O(aq) H3O +(aq) + Cl-(aq) (nearly 100% reaction)
A 1.0 mol/L solution of hydrochloric acid contains 1.0 mol/L hydronium ions.

23. Strong Acid- hydrochloric acid

24. The 6 strong acids you must memorize
There are 6 strong acids: Remember these.
Perchloric Acid
HClO4(aq)
Hydroiodic Acid
HI(aq)
Hydrobromic Acid
HBr(aq)
Hydrochloric Acid
HCl(aq)
Sulfuric Acid
H2SO4(aq)
Nitric Acid
HNO3(aq)

25. Weak acids
Weak acids react very little in water. Only a small percentage of the acid molecules form ions in water. Most of the acid molecules remain intact in solution.
Ethanoic acid is a weak acid (only about1% ionization)
CH3COOH(aq) + H2O(l) CH3COO-(aq) + H3O+(aq)
Note: A double headed arrow is used to represent weak acids to indicate that the solution is in equilibrium.

26. weak acid- Example Ethanoic acid

27. Strong Bases Dissociate completely into ions in water.
All oxides and hydroxides of the alkali metals (group 1) and the alkaline earth metals (group 2) below beryllium are strong bases.
examples
Some strong bases have very low solubility in water
Example Mg(OH)2(s).
However, the small amount that does dissolve dissociates completely, therefore they are still considered strong bases.

28. Weak Bases
A small amount of molecules of a weak base react in water to form OH- ions.
Aqueous ammonia is an example of a weak base. Only about 1% of the ammonia molecules in solution form hydroxide ions.

29. Examples of Weak Acids and Bases in Living Organisms
Citric acid
Ammonia
Amino acids
Ascorbic acid (vitamin C)

30. Questions in workbook

31. Monoprotic and Polyprotic Acids
Monoprotic acids have only 1 hydrogen atom per molecule that can ionize in water.
Example HCl
Polyprotic acids have 2 or more hydrogen atoms per molecule that can ionize in water.
Acids that have 2 hydrogens - diprotic acids.
Acids that have 3 hydrogens - triprotic acids.
Examples
Diprotic - H2SO4(aq) (Sulfuric Acid)
Trpotic-

32. Polyprotic Acid reactions
The number of hydrogens you have ionize is the number of steps there are in the reaction
As the acid continues to ionize the acid gets weaker and weaker
If the polyprotic acid is strong only the 1st step ionizes completely

33. Example- Diprotic Acid
Sulfuric acid is a strong diprotic acid. Only the first reaction however is 100% ionization.
H2SO4(aq) + H2O(l) H3O+(aq) + HSO4-(aq) (100% rxn)  
HSO4-(aq) + H2O(l) H3O+(aq) + SO42-(aq) (minimal rxn)  
Strong Acid
Weak Acid

34. Example- tripotic acid
Phosporic acid is a weak triprotic acid
H3PO4(aq) + H2O(l) H3O+(aq) + H2PO4-(aq) (weak acid)
H2PO4-(aq) + H2O(l) H3O+(aq) + HPO42-(aq) (weaker acid)
HPO42-(aq) + H2O(l) H3O+(aq) + PO43-(aq) (weakest acid)

35. Monoprotic and Polyprotic Bases
Monoprotic bases react with water in one step producing hydroxide ions.
Polyprotic Bases react with water in two or more steps producing hydroxide ions.

36. Example- diprotic base
Hydrazine N2H4(l) used in rocket fuel is a diprotic base.
N2H4(l) + H2O(l) N2H5+(aq) + OH-(aq)
N2H5+(aq) + H2O(l) N2H6+(aq) + OH-(aq)
As with polyprotic acids, the base that ionizes in the first step ionizes more completely than the base that ionizes in subsequent steps.

37. Example Sodium carbonate is another polyprotic base
First, in water sodium carbonate dissociates
Na2CO3(s) in water 2Na+(aq) + CO32-(aq)
The carbonate ion then reacts with water in two steps
CO32-(aq) + H2O(l) HCO3-(aq) + OH-(aq)
HCO3-(aq) + H2O(l) H2CO3(aq) + OH-(aq)

38. Acids and Base in Industry
Acids and bases have numerous industrial uses. Some of the most highly used are sulfuric acid and ammonia.

39. Sulfuric Acid in Industry

40. Ammonia in Industry
Used in fertilizers, explosives, refrigerants, and textiles.
Canada is the fifth largest producer of ammonia in the world.

41. Acid/Base spills Two methods for dealing with acid and base spills
Dilution
Neutralization

42. HNO3(aq) + NaOH(aq) NaNO3(aq) + H2O(l)
Neutralization
The reaction between an acid and a base produces an ionic compound (a salt) and water.
A salt is an ionic compound comprising of an anion from an acid and a cation from a base.
Acid Base Salt Water
HNO3(aq) + NaOH(aq) NaNO3(aq) + H2O(l)

43. H3O+(aq) + OH-(aq) 2H2O(l)
remember
Acids produce hydronium ions and bases produce hydroxide ions in solution.
When solutions containing hydronium and solutions containing hydroxide are mixed the ions react to form water.
H3O+(aq) + OH-(aq) 2H2O(l)

44. Do Section 6.2 Review P.226

45. 2H2O(l) H3O+(aq) + OH-(aq)
Acids, Bases, and pH
Ion concentrations in Water
Water is a molecular compound.
Contrary to previous study water does conduct electricity, but very weakly.
From this observation scientists infer that pure water self ionizes into hydronium and hydroxide. 
2H2O(l) H3O+(aq) + OH-(aq)

46. [H3O+(aq)] = [OH-(aq)] = 1.0 x 10-7 mol/L
However, only about two water molecules in a billion are ionized at any given time.
Chemists have determined that the concentration of hydronium ions in pure water at SATP is only 1.0 x 10-7 mol/L
[H3O+(aq)] = [OH-(aq)] = 1.0 x 10-7 mol/L

47. Acids have a higher concentration of H3O+(aq) than OH-(aq)
Bases have a higher concentration of OH-(aq) than H3O+(aq)

48. The pH Scale: Measuring by Powers of Ten
The pH scale or the power of hydrogen scale is a method that the strength of an acid or base is communicated.
acid neutral base

49. Ph scale The pH scale uses base 10 logarithms.
A base 10 logarithm of a number is the power to which you must raise ten to equal that number.
For example the log of 10 is 1 because 101 = 10. The log of 100 is 2 because 102 = 100.

50. pH is the negative base 10 logarithm of the molar concentration of hydronium ions in solution.
pH = -log [H3O+]
However, it is possible to have a negative pH or a pH greater than 14.
The concept of pH allows hydronium ion concentration to be expressed using positive numbers usually between 0 and 14

51. [H3O+(aq)] = [OH-(aq)] = 1.0 x 10-7 mol/L
Recall the concentration of hydronium ions in pure water at SATP was determined to be 1.0 x 10-7 mol/L
[H3O+(aq)] = [OH-(aq)] = 1.0 x 10-7 mol/L
Now if we were to determine the pH of water using this formula
  pH = -log [H3O+]
= -log [1.0 x 10-7]
= - [-7.00]
= 7.00

52. Sig. Digs. and pH
When reporting pH values, only the digits to the right of the decimal point are considered significant. Therefore a pH of 7.00 has only 2 sig digs.

53. Since pH is a log scale, each change in pH indicates a ten-fold increase in [H3O+]. A solution with a pH of 3.00 is 100 times more acidic than a solution with a pH of 5.00.
See sample problems p.229

54. Do practice problems p.230

55. pH Indicators
Indicators change color in acidic and basic solutions and have been standardized so that a particular color indicates a particular pH.
Universal indicator contains a number of indicators and has different characteristic colors over a wide range of pH values. It is available as a liquid or as pH paper.
Many naturally occurring indicators also exist like red cabbage.

57. pH Meters
pH meters are the quickest and most precise method of measuring pH.
A pH meter uses an ion-specific electrode that compares [H3O+] in the solution with a reference electrode.

58. Diluting Acids and Bases
Diluting and acid will increase its pH, but only up to a pH of 7.0.
Similarly, diluting a base can only reduce its pH up to a pH of 7.0.

59. Calculating pOH
Just as pH refers to the “power of hydrogen” or [H3O+], pOH refers to “power of hydroxide” or [OH-]
pOH = -log[OH-]
For example, Find the pOH of pure water.
pH = -log [OH-]
= -log [1.0 x 10-7]
= - [-7.00]
= 7.00
You can think of pOH as the opposite of pH.

60. Every change of 1 pOH represents a ten-fold change in [OH-]
If the pOH - >7.00 Basic
- < 7.00 Acidic
Every change of 1 pOH represents a ten-fold change in [OH-]
pOH of a solution can be found by subtracting the pH of a solution from 14.
For example:
If pH is 7.00 then pOH is 7.00.
If pH is then pOH is 4.00.
See table 6.8 on p.237 for more examples.
pH + pOH = 14.00

61. See sample problems P
Do Practice problems P.237

62. pH and Acid Deposition Normal rain water has a pH of 5.6
Due to acid deposition caused by industrial pollutants the average pH of rain in Ontario is That’s or 5 times more acidic than normal rainfall.

63. Oxides of sulfur produced by the burning of fossil fuels that contain sulfur are one of the major causes of acid precipitation. The oxides react with water in the air to form acids.
For example
SO2(aq) + H2O(l) H2SO4(aq)

64. There are 4 ways to prevent this reaction: 1
There are 4 ways to prevent this reaction: 1. Remove sulfur from fuel before it is burned 2. Use alternative energy sources 3. Reduce consumption of energy 4. Add scrubbers to smokestacks to remove oxides

65. The figure bellow show how scrubbers remove sulfur from fuels such as coal. The key is the addition of CaO(s). CaO(s) reacts with SO2(g) to form CaSO3(s) The calcium sulfite can then be washed away by water.

66. Calculating [H3O+] and [OH-] from pH and pOH
You can calculate [H3O+] and [OH-] by finding the antilog of the pH or pOH.
See sample problems p
Do practice problems p.241

68. Do Section 6.3 Review p.242 #1-11
Do Chapter 6 Review p.244 #2,3
Do Unit 3 Review p.248 # 2-5,7- 10,14,19,24,30,32-34,37,40