1. Ms. Kiely, IB Chemistry SL Coral Gables Senior High
Topic 8: Acids & Bases
Ms. Kiely, IB Chemistry SL Coral Gables Senior High

2. Topic 8 Review Questions
Bell-Ringer: Which species are a conjugate pair according to the Brønsted-Lowry theory?
A. CH3COOH and CH3CHO
B. NH3 and BF3
C. H2NO3+ and NO3–
D. H2SO4 and HSO4–
Homework:
Topic 7 Rebuild
Topic 8 Review Questions

3. Bell-Ringer: Which species are a conjugate pair according to the Brønsted-Lowry theory?
A. CH3COOH and CH3CHO
B. NH3 and BF3
C. H2NO3+ and NO3–
D. H2SO4 and HSO4–
Answer: D

4. 8.2: Acids and bases to memorize!
Table on Pg. 256 is very helpful! You should also be familiar with whether they are strong or weak Hydrochloric Acid
Ethanoic Acid/Acetic Acid
Nitric Acid
Sulfuric Acid Carbonic Acid
Phosphoric Acid
Hydroxide Sodium hydroxide Ammonia Ammonium Lithium hydroxide

5. 8.2: Properties of Acids and Bases
You will need to be familiar with:
Metal oxides
Hydroxides
Ammonia
Soluble carbonates (Na₂CO₃ and K₂CO₃)
Hydrogenated carbonates (NaHCO₃ and KHCO₃)
*Soluble bases are known as alkalis. When dissolved in water they all release the hydroxide ion OH⁻. The concentration of hydroxide, [OH⁻] in a substance is what determines how basic a substance is; the concentration of the hydrogen ion [H⁺] determines how acidic a substance is

6. Bell-Ringer
Which of the following is/are formed when a metal oxide reacts with a dilute acid?
I. A metal salt
II. Water
III. Hydrogen gas
A. I only
B. I and II only
C. II and III only
D. I, II and III
HOMEWORK:
Read 8.5 and go over Topic 8 Review Questions
Announcement:
Option A, B, C, or D

7. Bell-Ringer
Which of the following is/are formed when a metal oxide reacts with a dilute acid?
I. A metal salt
II. Water
III. Hydrogen gas
ANSWER
B. I and II only

8. NEED TO MEMORIZE THE THREE TYPES OF REACTIONS BY WHICH ACIDS FORM SALTS
1. Acid + metal → salt + hydrogen *salts are ionic compounds Just a metal! If it’s a metal bonded to a nonmetal or a polyatomic ion, then it is a “base” or a “carbonate” Acid + base → salt + water If it is not just a metal, and it is not a compound with a carbonate polyatomic anion in it, then it is a base Acid + carbonate → salt + water + carbon dioxide
A carbonate is any compound with the polyatomic anion carbonate, CO₃²⁻, in it.
A salt is always an ionic compound. It is either formed when the hydrogen of an acid is replaced by a metal or by any other positive ion.

9. Acid + base → salt + water
A little more informaion on acid and base reactions:
Acid + base → salt + water
1. All acid-base reactions can be represented by one common ionic equation that shows the net reaction clearly:
H⁺(aq) + OH⁻(aq)  H2O(l)
2. Acid-Base reactions are also known as neutralization reactions. They are exothermic. Heat of neutralization is the enthalpy change that occurs when an acid and a base react together to form one mole of water. For reactions between all strong acids and bases, the enthalpy change is very similar with delta H = -57 kJ/mol approximately- this is because the net reactions for different types of acid and base reactions is the same! It is always the production of water from hydrogen cations and hyroxide!

10. Chemical equation: HCl(aq) + NaOH(aq)  NaCl(aq) + H2O(l)
We can write all of these reactions with acids creating salts as ionic equations, where we break down any aqueous compound into it’s respective ions, and leave non-aqueous compounds in their regular form.
Chemical equation: HCl(aq) + NaOH(aq)  NaCl(aq) + H2O(l)
Ionic equation: H⁺(aq) + Cl⁻(aq) + Na⁺(aq) + OH⁻(aq)  Na⁺(aq) + Cl⁻(aq) + H2O(l)
Then, for the net ionic equation, we cancel out spectator ions: ions that exist in the same form on both sides of a chemical equation because they are unchanged during the reaction and do not affect equilibrium.
Net ionic equation: H⁺(aq) + Cl⁻(aq) + Na⁺(aq) + OH⁻(aq)  Na⁺(aq) + Cl⁻(aq) + H2O(l) H⁺(aq) + OH⁻(aq)  H2O(l)

11. Net ionic equations can be written for any chemical reaction
Net ionic equations can be written for any chemical reaction. They do not just apply to chemical equations where an acid and base react. The point we were trying to make before is that when an acid and a base react, the net ionic equation WILL ALWAYS BE: H⁺(aq) + OH⁻(aq)  H2O(l)
Let’s write net ionic equations for the other two types of formulas you must memorize for Topic 8:
1. Acid + Metal  Salt + Hydrogen gas 2HCl(aq) + Zn(s)  ZnCl2(aq) + H2(g)
2. Acid + Carbonate  Salt + Water + Carbon Dioxide 2HCl(aq) + CaCO3(aq)  CaCl2(aq) + H2O(l) + CO2(g)

12. The following might make a little more sense now that you understand what a net ionic equation is, and also understand that all acid and base reactions result in the same net ionic equation:
Acid-Base reactions are also known as neutralization reactions. They are exothermic. Heat of neutralization is the enthalpy change that occurs when an acid and a base react together to form one mole of water. For reactions between all strong acids and bases, the enthalpy change is very similar with H = -57 kJ/mol approximately- this is because the net reactions for different types of acid and base reactions is the same! It is always the production of water from hydrogen cations and hydroxide!

13. Acid and base reactions, a. k
Acid and base reactions, a.k.a neutralization reactions are often used in the lab to calculate the exact concentration of an acid or an alkali (base) when the other concentration is unknown.
Remember, the solution of known concentration is the standard solution.
The technique of acid-base titration seeks to reach the equivalence point (the point at which the acid and the base neutralize each other). An indicator is often used for this. Less often is litmus paper.

14. pH can be calculated using log:
8.3: The pH scale is a way of quantifying just how acidic or basic a substance is. pH is directly based on the concentration of H⁺ ions that are roaming in a substance.
pH can be calculated using log:
pH = -log10[H⁺]
Why are we using log for pH? Most of the acids we will encounter are weak acids, meaning that the H⁺ concentration within them expressed directly as mol dm-3 will produce numbers with LARGE negative exponents; for example the [H⁺] in our blood is 4.6 x 10-8 mol dm-3
Such a small number is not very user-friendly when trying to compare the strength of acids.
Note that logarithms in this topic are to base 10. Don’t confuse these with natural logarithms to base e, (ln).

15. We can determine the pH of a substance if we know the concentration of H⁺ in the substance by using the following formula:
pH=-log[H⁺]
We can also calculate for the concentration of H⁺ in a substance if we know the substance’s pH by using this formula:
[H⁺]=10⁻pH

16. The pH scale is constructed so that these numbers are an equal distance apart, representing values that are in an equal ratio. Therefore, a change of one pH unit represents a 10-fold change in the hydrogen ion concentration [H⁺].
For every 1 factor of change in pH, the concentration of H⁺ changes by a factor of 10:
For example, a pH of 1 = 10⁻¹ = 0.1 mol dm⁻³
a pH of 2 = 10⁻² = 0.01 mol dm⁻³
a pH of 3 = 10⁻³ = mol dm⁻³
etc.

17. Acidic Alkaline/Basic
Although the pH scale is theoretically infinite*, most acids and bases we encounter in IB Chem will have positive pH values and fall within the range 0-14:
Meaning the concentration of H⁺ will range from 101 mol dm-3 to mol dm-3 within the substances we will be dealing with in IB Chem.
*(yes, pH values can be negative, but not when the aqueous solution is with water, therefore we won’t be working with them in IB Chem)

18. PRACTICE: A sample of lake water was analysed at 298K and found to have
[H+] = 3.2 x 10-5 mol dm-3. Calculate the pH of this water and comment on its value.

19. PRACTICE: A sample of lake water was analysed at 298K and found to have
[H+] = 3.2 x 10-5 mol dm-3. Calculate the pH of this water and comment on its value.
ANSWER:
pH = -log[H⁺]
pH = -log[3.2 x 10-5]
pH = 4.49 or 4.5
At 298K (since the pH scale we follow is measured for substances at 298K), this pH suggests the lake is acidic.

20. PRACTICE: If the pH of a solution is changed from 3 to 5, deduce how the hydrogen ion concentration changes.

21. [H⁺] = 10⁻³ = 0.001 mol dm-3 & [H⁺] = 10-5 = 0.00001 mol dm⁻³
PRACTICE: If the pH of a solution is changed from 3 to 5, deduce how the hydrogen ion concentration changes.
Answer:
In this problem, the pH went from 3 to 5. Therefore, the pH has increased by a factor of 2 units, meaning the hydrogen ion concentration has decreased by a factor of
100 or 10⁻².
You can see this by applying the formula [H⁺]=10⁻pH for each of the pH values:
[H⁺] = 10⁻³ = mol dm-3 & [H⁺] = 10-5 = mol dm⁻³
Let’s double check: If indeed the hydrogen ion concentration decreased by a factor of 100, then we should be able to divide by 100 and get (since this is a decrease in [H⁺]):
0.001/100 =

22. PRACTICE: Determine the ratio of [H⁺] in bottled water to that in rain water.

23. PRACTICE: Determine the ratio of [H⁺] in bottled water to that in rain water.
Use formula [H⁺]=10⁻pH to determine the concentration of hydrogen ions in each one, and divide them as you would to determine a ratio:
[H⁺]= = or 1:100
[H⁺]=10-5.1

24. 8.3: Introduction to [OH⁻]
-We have been discussing how H⁺ is the ion that determines just how acidic a substance is. For example, the higher the concentration of H⁺, the lower the pH and the more acidic the substance is; the lower the concentration of H⁺, the higher pH, and the more basic the substance is.
-However, the hydroxide ion, OH⁻, is an ion that is often used to determine how basic a substance is, given it is available in the substance.
-In aqueous solutions where both ions are present, the relationship between [H⁺] and [OH⁻] is inverse: a low [H⁺] (high pH) means a high [OH⁻] (low pH) and vice versa.
-The substance is neutral if [H⁺] and [OH⁻] are equal.

25. At 298K, Kw = [H⁺][OH⁻] = 1.00 x 10⁻¹⁴
-The substance is neutral if [H⁺] and [OH⁻] are equal. For instance, distilled water is neutral, having a pH of 7.
-Since most acid-base reactions involve the ionization of H⁺ and OH⁻ in aqueous solution (a solution of distilled water), we can use the ionic product constant of water, Kw, to help us calculate the concentrations of H⁺ and OH⁻ in a substance.
-Kw is basically another way of solving for concentration, but in this case we can use it to not only get information on the concentration of H⁺, but also of OH⁻.
At 298K, Kw = [H⁺][OH⁻] = 1.00 x 10⁻¹⁴
Distilled water is neutral because it has an equal concentration of [H⁺] and [OH⁻], meaning they each respectively equal 1.00 x 10⁻⁷ in this case.

26. At 298K, Kw = [H⁺][OH⁻] = 1.00 x 10⁻¹⁴
We can manipulate this formula for the ionic constant of water to determine the concentration of either [H⁺] or [OH⁻], since we know that together their product must equal 1.00 x 10⁻¹⁴.
PRACTICE: A sample of blood at 298K has [H⁺] = 4.60 x 10⁻⁸ mol dm⁻³.
Calculate the concentration of OH⁻ and state whether the blood is acidic, neutral, or basic.
Kw = [H⁺][OH⁻] = 1.00 x 10⁻¹⁴
Kw = [4.60 x 10⁻⁸][OH⁻] = 1.00 x 10⁻¹⁴
[OH⁻] = x 10⁻¹⁴ = x 10⁻⁷
4.60 x 10⁻⁸
The blood is basic, because the [OH⁻] is greater than the [H⁺].

27. Summary of steps in calculations of H+, OH-, and pH

28. Bell Ringer
Which are acid-base pairs according to the Brønsted‒Lowry theory?
I. HNO3/NO-3
II. H3O+/OH-
III. HCOOH/HCOO-
A. I and II only
B. I and III only
C. II and III only
D. I, II and III

29. Bell Ringer
Which are acid-base pairs according to the Brønsted‒Lowry theory?
I. HNO3/NO-3
II. H3O+/OH-
III. HCOOH/HCOO-
ANSWER
B. I and III only

30. 8.4: Strong and Weak Acids

31. 8.4: Strong & Weak Acids and Bases
Whether an acid or base is strong or weak will depend on the extent to which the acid or base ionizes in water.
-If an acid is entirely soluble (dissolves entirely) in aqueous solution, then it will completely ionize; meaning it will release all of its H⁺ ions. The more H⁺ ions, the stronger the acid.
-If the acid is not very soluble, it will not easily ionize, therefore not release many H⁺ ions. This would be defined as a weak acid.
The same goes for bases, except instead of H⁺, it would be in the context of OH⁻ ions.
Do not confuse acid/base strength with its concentration of hydrogen or hydroxide ions, which only determine pH. STRENGTH IS DETERMINED BY THE ACID’S OR BASE’S ABILITY TO DISSOCIATE IN AQUEOUS SOLUTION.

33. A strong acid is a good proton donor and has a weak conjugate base.
A strong base is a good proton acceptor and has a weak conjugate acid.
A weak acid is a bad proton donor and has a strong conjugate base. A weak base is a bad proton acceptor and has a strong conjugate acid. Reactions with weak acids and bases are considered equilibrium reactions that shift to the left.

34. 8.4: Strong & Weak Acids and Bases
As we just discussed, strong acids and bases will contain a higher concentration of ions than weak acids and weak bases. This can thus be used to help us identify whether an acid or a base we are working with is strong or weak. Three factors can be used:
1. Electrical conductivity 2. Rate of reaction 3. pH
The electrical conductivity of a solution depends on the concentration of mobile ions. Strong acids and bases will show higher conductivity than weak acids and bases of the same concentration since the molecules of strong acids and bases dissociate into more ions than those of weak acids and bases.
This means anions are roaming in these aqueous solutions! Anions are negatively charged particles = flow of negative charge = electricity!

35. 8.4: Strong & Weak Acids and Bases
The rate of reaction of an acid-base reaction will be faster for those that have strong acids/bases when compared to those of weak acids/bases, since strong acids/bases have more particles due to dissociation of ions. (More particles = higher frequency of collisions)
The pH of a solution is a direct indicator of the hydrogen ion concentration. We can therefore use the pH scale to compare the strengths of acids, providing there are of equal molar concentration. The higher the hydrogen ion concentration, the lower the pH value.

36. PRACTICE:
An example of a strong acid solution is perchloric acid, HClO4, in water. Which statement is correct for this solution?
A. HClO4 is completely dissociated in the solution.
B. HClO4 exists mainly as molecules in the solution.
C. The solution reacts only with strong bases.
D. The solution has a pH value greater than 7.

37. PRACTICE:
An example of a strong acid solution is perchloric acid, HClO4, in water. Which statement is correct for this solution?
ANSWER: A. HClO4 is completely dissociated in the solution.
B. HClO4 exists mainly as molecules in the solution.
C. The solution reacts only with strong bases.
D. The solution has a pH value greater than 7.