1. Acids and Bases

2. Topic: Acids& Bases in a chemical reaction
Unit: Acids and Bases
Topic: Acids& Bases in a chemical reaction
Objectives:
To understand the definition of an acid and a base
To learn how to identify acids and bases in a chemical reaction
To learn how to identify the conjugate acid and conjugate base in a chemical reaction

3. Quickwrite Answer one of the questions below in 1-2 sentences:
What do you know about acids???
What are some acids you have heard of???
What do you know about bases???
What are some bases you have heard of??

4. Acids and Bases Acids are very important substances
All rain is that falls from sky comes to us slightly acidic
They cause lemons to be sour
In fact, acids were first recognized as substances that taste sour
Vinegar tastes sour because acetic acid
Lemons taste sour because of citric acid
Bases or alkalis, are characterized by their bitter taste and slippery feel

5. The Arrhenius Model
The first person to notice the nature of acids was Svante Arrhenius with his experiments with electrolytes
Arrhenius postulated that acids produce hydrogen ions (H+) in aqueous solution and bases produce hydroxide ions (OH-) in solution H+ H+ H+ H+ H+ H+
OH-
OH-
OH-
OH-
OH-
OH-

6. The Arrhenius Model
For Example, when hydrogen chloride gas is dissolved in water, each molecule produces ions as follows:
HCl(g)  H+(aq) + Cl-(aq)
This solution is the strong acid known as hydrochloric acid
On the other hand, when sodium hydroxide is dissolved in water
NaOH(s)  Na+(aq) + OH-(aq)
This solution called a strong base

7. What’s the difference between an Arrhenius acid and a base?
Acids produce ______ions (H+) when dissolved in water and bases produce _____(OH-) ions when ______in water
Ex: HCl(g)  H+(aq) + Cl-(aq)
NaOH(s)  Na+(aq) + OH-(aq
hydrogen
Answer Bank
Donor
hydrogen
Proton
hydroxide
Cl –
Added
hydronium
Acceptor
dissolved
NH4+
hydroxide
dissolved

8. The BrØnsted-Lowry Model
The Arrhenius concept of acids and bases is limited because it only involves the hydroxide ion - only 1 kind of base - those that produce hydroxide ions
A more general definition of acids and bases was suggested by the Danish chemist Thomas Lowry
In the BrØnsted-Lowry model, an acid is a proton (H+) donor and a base is a proton acceptor
The general reaction is:
HA(aq) + H2O(l)  H3O+(aq) + A-
Acid
Base
Conjugate
Acid
Conjugate
Base

9. The BrØnsted-Lowry Model
HA(aq) + H2O(l)  H3O+(aq) + A-
According to the Bronsted-Lowry model, the general reaction that occurs when an acid is dissolved in water can best be represented as an acid (HA) donating a proton to the base (a water molecule)
Notice, the water molecule accepts the proton and does not produce a +1 charge

10. The Bronsted-Lowry Model
Cl-
Cl- H H H H+ H+ H H H H H H H H
HCl(aq) + H2O(l)  H3O+(aq) + Cl-
Acid
Donates proton
Base
Accepts proton

11. What is the difference between Bronstead-Lowry acid and base?
A Bronstead-Lowry acid is a proton (H+) _____and a Bronstead-Lowry base is a proton______
HA(aq) + H2O(l)  H3O+(aq) + A-
Water acts as a base even though it does not produce ______ ions (OH-)
When water accepts a protons it forms the ________ion (H3O+)
donor
Answer Bank
Donor
hydrogen
Proton
hydroxide
Cl –
Added
hydronium
Acceptor
dissolved
NH4+
acceptor
hydroxide
hydronium

12. The Bronsted-Lowry Model
An easy way to identify the acid and base in an acid-base reaction is to count the number of hydrogen atoms in each reactant and product
Consider the reaction below:
HCl NH3  NH Cl-
HCl has 1 hydrogen atoms and loses one to become Cl-
NH3 has 3 hydrogen atoms gains one to become NH4+
4 H atoms
4 H atoms
4 H atoms
4 H atoms
4 H atoms
4 H atoms
4 H atoms
1 H atoms
4 H atoms
3H atoms
3H atoms
3H atoms
3H atoms
3H atoms
3H atoms
3H atoms
3H atoms
3H atoms
4H atoms
0H atoms

13. The Bronsted-Lowry Model
Recall, a Bronstead-Lowry acid is a proton (H+) donor and a Bronstead-Lowry base is a proton acceptor
Using this definition you can see that HCl donates one H+ to NH3 so, HCl is the acid and NH3 is the base
HCl NH3  NH Cl-
Donates a H+
Acid
Accepts a H+
Base

14. Practice:
Using your Brontead-Lowry definition of acid and bases, Identify the acid and base in following equations:
1) HCl NH3  NH Cl –
2) HNO3 + H2O  H3O+ + NO3-
acid
base
HCl
NH3
acid
base
HNO3
H2O

15. Conjugate Acids & Bases
The reaction below is reversible:
HCl NH3  NH Cl –
But what happens when the reverse reactions takes place?
The ions, NH4+ and Cl- act as the acid and base
NH4+ becomes the conjugate acid by donating a proton
Cl - becomes the conjugate base by accepting the proton

16. Conjugate Acids & Bases
HCl NH3  NH Cl –
A conjugate acid is the molecule or ion formed when a proton is added to a base, in this case NH4+
A conjugate base is what remains of an acid molecule or ion after a proton is lost , in the is case Cl –
Acid
Base
Conjugate Acid
Conjugate Base

17. What is the difference between a conjugate acid and base?
HCl NH3  NH Cl –
A conjugate acid is the molecule or ion formed when a _____ is added to a base, in this case____
conjugate base is what remains of an acid molecule or ion after a proton is _____, in the is case____
proton
Answer Bank
Donor
hydrogen
Proton
hydroxide
Cl –
Added
lost
hydronium
Acceptor
dissolved
NH4+
NH4+
lost
Cl-

18. Conjugate Acids & Bases
HCl NH3  NH Cl –
The acid HCl and conjugate base Cl – form what is called the conjugate acid-base pair
The base NH3 and conjugate acid NH4+ form what is called the conjugate base-acid pair

19. Conjugate Acids and Bases
conjugate acid-base pair
HCl(aq) NH3 (l)  NH4+ aq) + Cl-
conjugate base-acid pair

20. Practice:
Using the bronstead lowry definiton, identify the acid, base, conjugate acid and conjugate base in the reactions below
NH H2O ↔ NH OH-
Acid
Base
Conjugate Acid
Conjugate base
NH4+
OH-
H2O
NH3

21. Summarize: An acid is any substance that donates a _______
A base is a proton______
Given the equation:
HCl(aq) + H2O(l) → H3O+(aq) + Cl-(aq), H2O may be classified as a ______ because it accepts a proton
In the above equation, HCl is an ____ because it is donating a proton
Answer Bank
Hydrogen(H+)
base
Hydroxide(OH–)
Donates
acceptor
hydronium
proton

22. Topic: Acid Concentration and pH
Unit: Acids and Bases
Topic: Acid Concentration and pH
Objectives:
To understand what determines the strength of an acid and base
To understand ion product constant (K) for water
To learn how to calculate the hydrogen and hydroxide concentration given the product constant for water
To learn how to calculate pH or pOH given K

23. Quickwrite Answer one of the questions below in 1-2 sentences:
Have you ever bitten into a lemon, what did it taste like???
Have you ever felt bleach?? What did it feel like????

24. Acid Strength
Acid strength is determined by the amount or concentration of Hydrogen ions [H+] in solution
Strong acids completely disassociate and ionize (dissolves) to produce H+ ions
Versus, a weak acids only slightly disassociate and ionize (dissolve) to produce H+ ions

25. + Weak Acids like HF only slightly disassociate ad ionize (dissolve)
In other words, weak acids will produce less hydrogen ions when dissolved in water HF H F H+ H F H F F- F- F- H+ H+ H F F H F- HF F- H+ +

26. + Strong acids Completely dissolve or disassociate and ionize in water
In other words, strong acids will completely more hydrogen ions when dissolved in water
HCl
Cl- H+
Cl-
Cl-
Cl- H+ H+ H+ H+
Cl-
Cl-
Cl- H+ H+
HCl
Cl- H+ +

27. What’s the difference between a weak acid and a strong acid?
Acid strength is determined by the amount of ________ ions in solution
Strong acids ________disassociate and ionize (dissolves) to produce H+ ions
Versus, a weak acids only _____disassociate and ionize (dissolve) to produce H+ ions
Hydrogen (H+)
Answer Bank
Hydrogen (H+)
Greater than
H2SO4
completely
equal
H2CO3
slightly
Concentration
Less than
completely
slightly

28. Strong and Weak Acids Strong acids Weak Acids HCl Hydrochloric Acid
HC2H3O2
Acetic Acid
H2SO4
Sulfuric Acid
H3PO4
Phosphoric Acid
HNO3
Nitric Acid
H2CO3
Carbonic Acid

29. What are some strong and weak acids?
Strong acids
Weak Acids
HCl
Hydrochloric Acid
HC2H3O2
Acetic Acid
________
Sulfuric Acid
H3PO4
Phosphoric Acid
HNO3
Nitric Acid
_________
Carbonic Acid
Answer Bank
Hydrogen (H+)
Greater than
H2SO4
completely
equal
H2CO3
slightly
Concentration
Less than
H2SO4
H2CO3

30. Water as an Acid and a Base
A substance is said to be amphoteric if it can behave as an acid or as a base
Water is the most common amphoteric substance
The following reactions illustrates this point:
H2O(l) ↔ H+(aq) OH-(aq)
Pure water only contains the hydrogen and hydroxide ions--in small amounts!

31. [OH-] = (1.0 x 10-7 M) [H+] = (1.0 x 10-7 M)
Water as an Acid & a Base
Pure water contains H+ ions in it
This concentration is [H+] = 1.0 x 10-7 M
Pure water contains OH- ions in it
This concentration is
[OH-] = 1.0 x 10-7 M
It is important to realize that these concentration values are constant and equal
[OH-] = (1.0 x 10-7 M)
[H+] = (1.0 x 10-7 M) H+
OH-
OH- H+ H+
OH-
OH- H+
OH- H+
OH- H+

32. Water as an Acid & a Base = 1.0 x 10 -14 M
We can find this constant by multiplying the concentrations of H+ & OH-
Or, [H+] [OH-] =
(1.0 x 10-7 M)(1.0 x 10-7 M)
= 1.0 x M
[H+] [OH-] = (1.0 x M) H+
OH- H+
OH- H+ H+
OH-
OH- H+
OH- H+
OH-

33. Water as an Acid and a Base
We call this constant Kw, or the ion product constant for water
So now we can simply the expression into:
[H+] [OH-] = (1.0 x M) = Kw
The constant Kw is always equal to
1.0 x M

34. Water as an Acid and a Base
This means that if the [H+] concentration goes up, then [OH-] concentration goes down, resulting in an acidic solution
Or if we add more base [OH-], this will cause the hydrogen ion concentration [H+] to go down, resulting in a basic solution
[H+] [OH-] = (1.0 x M) = Kw

35. What is the ion-product constant?
Kw is the ion product constant for water
It is the ___________of [H+] [OH-] ions in water
It is equal to:
Kw = (1.0 x M) = [H+] [OH-]
Answer Bank
Hydrogen (H+)
Greater than
H2SO4
completely
equal
H2CO3
slightly
Concentration
Less than
concentration

36. the solution is neutral
Water as an Acid & a Base
If [H+] = [OH-] then the solution is neutral
If [H+] > [OH-] then the solution is acidic
If [H+] < [OH-] then the solution is basic
If [H+] > [OH-] then
the solution is acidic
If [H+] < [OH-] then
the solution is basic
If [H+] = [OH-] then
the solution is neutral H+ H+ H+
OH-
OH-
OH- H+ H+
OH-
OH-
OH- H+ H+ H+ H+ H+ H+
OH-
OH-
OH-
OH-
OH-
OH- H+ H+ H+ H+
OH-
OH-
OH-
OH-
OH-
OH- H+ H+ H+

37. What determines whether a solution will be acidic or basic?
equal
If [H+] is ______ to [OH-] then the solution is neutral
If [H+] is ______ _____ [OH-] then the solution is acidic
If [H+] is _____ _____ [OH-] then the solution is basic
greater than
Answer Bank
Hydrogen (H+)
Greater than
H2SO4
completely
equal
H2CO3
slightly
Concentration
Less than
less than

38. Practice: Solution: Because 1.0 x 10 -5 M > 1.0 x 10 -9 M
A solution contains a hydrogen ion concentration of 1.0 x M ( [H+] = 1.0 x M ) and a hydroxide ion concentration of 1.0 x 10-5 M ( [OH-] = 1.0 x M ) Is the solution basic or acidic?
Solution:
Because 1.0 x M > 1.0 x M
In other words, because [OH-] is greater than [H+], the solution is basic

39. Practice: 1.0 x 10 -5 M [OH-] solution:
Calculate the [H+] ion concentration for a
1.0 x M [OH-] solution:
Recall: Kw = (1.0 x M) = [H+] [OH-]
We know that Kw = (1.0 x M) = [H+] [OH-]
so we need to calculate and solve for [H+]
[H+] = 1.0 x = 1.0 x 10 –9 M
1.0 x 10-5
We know that Kw = (1.0 x M) = [H+] [OH-]
so we need to calculate and solve for [H+]
1.0 x M =
[H+]
[OH-]
1.0 x M

40. Practice: 10 M [H+] solution:
Calculate the [OH-] ion concentration for a
10 M [H+] solution:
Recall: Kw = (1.0 x M) = [H+] [OH-]
10 M [H+] Is the solution basic or acidic?
We know that Kw = (1.0 x M) = [H+] [OH-]
so we need to calculate [OH-]
[OH-] = x = 1.0 x = 1.0 x 10 –15 M
[H+]
We know that Kw = (1.0 x M) = [H+] [OH-]
so we need to calculate [H+]
[H+] = 1.0 x = 1.0 x = 1.0 x 10 –9 M
[OH-] x 10-5

41. pH Scale
Rather than use scientific notation, the pH scale was developed to simplify things
pH is simple way to describe the very wide range of [H+] concentration
pH is the negative logarithm of [H+]
It is expressed as pH = -log [H+]
pH values have no units
However, to calculate pH, [H+] must be in molarity
In other words, if you know [H+], you can find pH

42. pH Scale To calculate pH, you will need a calculator with a log button
What is the pH of water?
Remember, water has a molarity or [H+] concentration of 1.0 x 10-7
To calculate the pH of water, you would take the – log [H+] , or pH = – log (1.0 x 10-7) = 7
7 is a neutral pH
Anything below 7 is acidic and anything above seven basic

43. pH

44. What’s the difference between acidic and basic?
Acidic solutions have a pH _____ _____ 7 and basic solutions have a pH ____ ____ 7 (alkaline)
Acids also have a ____ taste to them and bases have bitter taste smooth ______feel to them
less than
Answer Bank
concentration
Greater than(2)
Basic
sour
pOH
equal
logarithm
acidic
Less than (2)
slippery
greater than
sour
slippery

45. Practice: Calculate the pH of a 0.0100 M HCl solution, [H+] = 0.0100 M
pH = - log [H+]
Remember, pH = - log [H+]
So, pH = - log (0.0100) = 2

46. Practice: Calculate the pH of a 0.005 M HCl solution, [H+] = 0.005 M
pH = - log [H+]
Remember, pH = - log [H+]
So, pH = - log [0.005] = ????

47. pOH We can also use the log scale to calculate pOH
For example: pOH = - log [OH-]
Therefore, a solution that has a molarity or hydroxide concentration of [OH-] = 1.0 x M has a pOH of:
-log [OH-] = -log(1.0 x M ) = 12.00
Or pOH = 12

48. Remember, pOH = - log [OH-]
Practice:
Calculate the pOH for a solution that has hydroxide concentration of [OH-] of x 10-3 M
Remember, pOH = - log [OH-]
So, pOH = - log (1.0 x 10-3 M) = 3.0

49. pH & pOH There is a convenient relationship between pH and pOH
If you remember your Kw equation where Kw = [H+] [OH-] = 1.0 x you can calculate pOH from pH
By taking the negative log of both sides log ( [H+] [OH-] ) = -log (1.0 x 10-14)
We get –log [H+] –log [OH-] = -log (1.0 x 10-14) = 14
This gives us the equation pH + pOH = 14
So, this means that if you know either pH or pOH for a solution you can calculate the other

50. Practice: The pH of blood s about 7.4 (pH = 7.4) What is the pOH?
pH + pOH = 14
We just learned that pH + pOH = 14
We know the pH of blood = 7.4
Plug this value into our equation we get:
7.4 + pOH = 14
pOH = = 6.6

51. Summarize: An acid is any substance that donates a _______
Acids have a ______ taste and produce______ ions in solution
KOH is strong base because it easily releases _______ions
HCl is a strong acid because it completely releases releasing _____ ions
If [H+] is > [OH-] then the solution is_______
Answer Bank
Hydrogen (H+)
slippery
sour
Hydroxide (OH–)
donates
hydronium
proton