1. Acids and Bases Objectives
An Introduction
Objectives
Identify the physical and chemical properties of acids and bases.
Classify solutions as acidic, basic or neutral.
Compare the Arrhenius acid and Brønsted-Lowery models of acids and bases. .

2. Acids and Bases Not a good idea . .
An Introduction
Not a good idea . .
Citrus fruits contain citric acid – so how do they taste?
A common characteristic of acids is they have a sour taste & will conduct electricity.
All soaps are bases – in a shower soaps tend to be slippery.
If you have ever had the joy of having your mouth washed out with soap, it tastes bitter & will conduct electricity. .
Tasting an unknown substance is a no-no!

3. Acids and Bases
An Introduction
So how . .
So other than taste and feel, how does one determine if a solution is an acid or a base?
Acids contain H+ ions.
Bases contain OH- ions.
There are two models of acids and bases
Arrehenius Model
Brønsted-Lowery Model .

4. Acids and Bases
An Introduction
So how . .
Swedish chemist Svante Arrhenius came up with the first acid/base model in 1883.
An acid is a substance that contains hydrogen and produces hydrogen ions in aqueous solutions.
A base is a substance that contains the hydroxide group and produces hydroxide ions in aqueous solutions.
This known as the Arrhenius model. .

5. Acids and Bases So how . . Looking at an acid.
An Introduction
So how . .
Looking at an acid.
HCl(g)  H+(aq) + Cl-(aq)
We see when hydrogen chloride is dissolved in water we get hydrogen ions and chloride ions.
Looking at a base.
NaOH(s)  Na+(aq) + OH-(aq)
Here solid sodium hydroxide is dissolved in water we get sodium ions and hydroxide ions. .

6. Acids and Bases
An Introduction .

7. Acids and Bases Always the exceptions . .
An Introduction
Always the exceptions . .
As it turns out, the Arrhenius was not without fault.
NH3 does not contain OH-, but will produce a base when dissolved in water.
As so often happens in science, two scientist came up with the same model independently.
Danish chemist Johannes Brønsted and English chemist Thomas Lowry. .

8. Acids and Bases Exceptions create new theories . .
An Introduction
Exceptions create new theories . .
In the Brønsted-Lowry model, the focus is on the hydrogen ion.
An acid is a hydrogen-ion donor.
A base is a hydrogen-ion acceptor.
Acid
Base
HX is an acid because it donates a H+ to H2O forming H3O+.
The H2O is the base because it can accept an H+. .

9. Acids and Bases Exceptions create new theories . .
An Introduction
Exceptions create new theories . .
As noted by the , the reaction can work in either direction - the H+ can be donated by the HX, or the X- can get back with a H+ from the H3O+ to form HX.
Acid
Base
Conjugate acid
Conjugate base
Since the H3O+ is a product and can give up a H+, it is called a conjugate acid.
Since the X- is a product and can accept a H+, it is called a conjugate base. .

10. Acids and Bases Exceptions create new theories . .
An Introduction
Exceptions create new theories . .
Notice that the reactant base becomes the product conjugate acid.
Acid
Base
Conjugate acid
Conjugate base
The reactant acid becomes the product conjugate base. .

11. Acids and Bases Exceptions create new theories . .
An Introduction
Exceptions create new theories . .
We always have acid-base pairs.
The HF is the acid in the forward reaction and it produces the F- conjugate base.
The H2O is the base in the forward reaction and it produces the H3O+ conjugate acid. .

12. Acids and Bases Exceptions create new theories . .
An Introduction
Exceptions create new theories . .
The Brønsted-Lowry Model works for all acid & bases of the Arrhenius Model – but will it work for those that did not work with the Arrhenius Model?
Conjugate acid
Base
Acid
Conjugate base
The NH3 accepted a H+, making NH3 a base and NH4 a conjugate acid.
The H20 donates a H+, thus making H2O an acid and OH- a conjugate base. .

13. Acids and Bases Objectives
Strengths of Acids & Bases
Objectives
Relate the strength of an acid or base to its degree of ionization.
Compare the strength of a weak acid with the strength of its conjugate base.
Compare the strength of a weak base with the strength of its conjugate acid.
Explain the relationship between the strength of acids and bases and the values of their ionization constants. .

14. Acids and Bases If you had to drink one or the other . .
Strengths of Acids & Bases
If you had to drink one or the other . .
When working with a car battery, we are warned to not splash any of the liquid in the battery onto our skin, for it may burn us.
On the other hand, we use vinegar (acetic acid) as part of a salad dressing, or to put on our greens (yuck).
If we had .1M solutions of hydrochloric acid and acetic acid, we would find that hydrochloric acid is a good conductor of electricity, but that the acetic acid is not. .

15. Acids and Bases If you had to drink one or the other . .
Strengths of Acids & Bases
If you had to drink one or the other . .
What is it that is required to conduct electricity?
So if ions are required to conduct electricity, then HCl(aq) must have lots of ions and acetic acid has few ions.
HCl is made up of ions of hydrogen and chlorine.
Acids that ionize completely are strong acids. .

16. Acids and Bases If you had to drink one or the other . .
Strengths of Acids & Bases
If you had to drink one or the other . .
HCl(aq) + H2O(l)  H3O+(aq) + Cl-(aq)?
Notice that this reaction is one way – there is no (or very little) reverse reaction.
On the other hand looking at the reaction for acetic acid, notice it is a reversible reaction.
A reversible reaction never completely ionizes.
Acids which produce few ions (partially ionizes) are weak acids . .

17. Acids and Bases Hydrochloric Acid vs. Acetic Acid .
Strengths of Acids & Bases
Hydrochloric Acid vs. Acetic Acid .

18. Acids and Bases If you had to drink one or the other . .
Strengths of Acids & Bases
If you had to drink one or the other . .
How about strong and weak bases?
NaOH(aq)  Na+(aq) + OH-(aq)?
Sodium hydroxide is a strong base because it completely disassociates.
Like a strong acid, it is a one way reaction.
Bases which completely disassociates into metal ions and hydroxide ions are strong bases. .

19. Acids and Bases If you had to drink one or the other . .
Strengths of Acids & Bases
If you had to drink one or the other . .
Bases which partially disassociates to form a conjugate acid and a conjugate base are weak bases.
Conjugate acid
Base
Acid
Conjugate base .

20. Acids and Bases Weak or Strong . .
Strengths of Acids & Bases
Weak or Strong . .
When speaking of acids or bases you will hear them described as a weak acid or a strong acid (or a weak base or strong base).
This is different that concentrated or diluted you might use to talk about your tea!
Strong and weak are used to refer to the degree to which an acid or a base will separate into ions. .

21. Acids and Bases Objectives Explain the meaning of pH and pOH.
What is pH?
Objectives
Explain the meaning of pH and pOH.
Relate pH and pOH to the ion product for water.
Calculate the pH and pOH of aqueous solutions. .

22. Acids and Bases Ion Product Constant for Water
An Introduction
Ion Product Constant for Water
When we first started taking about acids and bases we used the following equation:
This tells us that water disassociates into ions.
What is the concentration of ions?
For pure water at 298°K there are 1.0x10-7 M H+ ions and 1.0x10-7M OH- ions. .

23. Acids and Bases Ion Product Constant for Water
An Introduction
Ion Product Constant for Water
The ion product constant for water is expressed as Kw = (H+)(OH-) or (1.0x10-7)(1.0x10-7) = 1.0x10-14
As an acid increases the H+, then the OH- will decrease, but the product of the two will always be 1.0x10-14
The concentration of H+ or OH- are always small numbers (expressed in scientific notation). .

24. Acids and Bases pH and pOH
An Introduction
pH and pOH
An easier way to express the number of ions is to use the log scale.
The pH of a solution is the negative logarithm of the hydrogen ion concentration.
pH = -log[H+]
pH goes from 0.0 (a very strong acid) to 7.0 (neutral) to 14.0 (a very strong base) .

25. Acids and Bases
An Introduction .

26. Acids and Bases pH and pOH
An Introduction
pH and pOH
What is the pH of a solution which has H+ = 1.0x10-7M?
Press the CHS (change sign) key
Press the “log” key.
Enter 1.0x10-7 into your calculator and press = 7
What is the pH of a solution which has H+ = 3.0x10-6M?
pH = -log(3.0x10-6)
= 5.5 .

27. Acids and Bases pH and pOH
An Introduction
pH and pOH
You can perform the same calculation with pOH:
pOH = -log[OH-]
pOH is not often done
Could be useful in checking your work:
pH + pOH = 14 .

28. Acids and Bases Objectives
Acid & Base Neutralization
Objectives
Write chemical equations for neutralization reactions.
Describe how pH indicators work.
Explain how neutralization reactions are used in acid-base titrations. .

29. Acids and Bases Determining pH
Acid & Base Neutralization
Determining pH
There several ways to determine the pH of an acid or a base.
The simplest is a pH meter – a probe is placed in the solution, the meter reads the pH.
Other methods use color to indicate pH.
Red litmus paper turns blue in the presence of a base (it remains red in an acid).
Blue litmus paper turns red in the presence of a acid (it remains blue in a base). .

30. Acids and Bases
Acid & Base Neutralization .

31. Acids and Bases Titration of an Acid and a Base
Acid & Base Neutralization
Titration of an Acid and a Base
Titration is a method for determining the concentration (M) of a solution by reacting a known volume of the solution with a solution of known concentration.
Measure a volume of the solution of unknown concentration into a beaker – measure the pH.
Fill a buret with a solution of known concentration (if the unknown is an acid, the known would be a base). .

32. Acids and Bases Titration of an Acid and a Base
Acid & Base Neutralization
Titration of an Acid and a Base
Slowly (drop by drop) add (and stir) the “standard solution” to the unknown solution. Measure the pH after each addition of the standard solution.
4. Stop when the number of moles of H+ is equal to the number of moles of OH-. This is known as the equivalence point.
Note that the equivalence point may not be at pH = 7. .

33. Acids and Bases
Acid & Base Neutralization
Notice that the pH slowly climbed until just before there were equal H+ and OH- ions, and then it went vertical. .

34. Acids and Bases
Acid & Base Neutralization
Here we have the titration curve of 25ml of methanoic acid.
The equivalence point was reached with 18.28mL of .1000M NaOH.
How do we determine the concentration of the CHOOH? .

35. Acids and Bases
Acid & Base Neutralization
25mL CHOOH reaches end-point with 18.28mL of .1000M NaOH – what is the concentration of CHOOH?
Create the balanced equation for the reaction:
CHOOH(aq) + NaOH(aq)  CHOONa(aq) + H2O(l)
We know that 18.28mL of .1000M NaOH was used, so we need to know is how many moles of NaOH there are.
That is going to take a couple of steps! .

36. Acids and Bases Molarity = moles/liter
Acid & Base Neutralization
25mL CHOOH reaches end-point with 18.28mL of .1000M NaOH – what is the concentration of CHOOH?
Convert mL to L
Convert from L to mole .

37. Acids and Bases CHOOH(aq) + NaOH(aq)  CHOONa(aq) + H2O(l)
Molarity = moles/liter
Acid & Base Neutralization
25mL CHOOH reaches end-point with 18.28mL of .1000M NaOH – what is the concentration of CHOOH?
Use stoichiometry to determine the number of moles of CHOOH that will react with 1.828x10-3 mol NaOH
Convert from mol to M (molarity) .

38. Acids and Bases
Acid & Base Neutralization
25mL HCl reaches end-point with 38.28mL of .4370M NaOH – what is the concentration of HCl?
HCl(aq) + NaOH(aq)  NaCl(aq) + H2O(l) .

39. Acids and Bases RbOH + HF  H20 + RbF
33.21mL of .3020M RbOH reaches an endpoint with
20.00mL of HF – what is the concentration of HF? .

40. Acids and Bases NaOH + HBr  H20 + NaBr
14.76mL of .4122M HBr reaches an endpoint with
35.00mL of NaOH. What is the NaOH concentration? .

41. Acids and Bases Sr(OH)2 + HCl  H2O + SrCl2
43.03mL of .1159M HCl reaches an endpoint with
20.00mL of Sr(OH)2. What is the Sr(OH)2 concentration? 2 2 .

42. Acids and Bases HF + NaOH  NaF + H2O
13.51mL of .1500M NaOH reaches an endpoint with
20.00mL of HF. What is the HF concentration? .

43. Acids and Bases 2 HCl + Ba(OH)2  BaCl2 + H2O
43.09mL of .1500M Ba(OH )2 reaches an endpoint with
26.06mL of HCl. What is the HCl concentration? 2 .

44. Acids and Bases HCl + NaOH  NaCl + H2O
13.09mL of 3.500M HCl reaches an endpoint with
26.04mL of NaOH. What is the NaOH concentration? .