Unit 14: Acids & Bases

Chapter 19

Review: Naming an Acid

Binary acids (H + nonmetal): hydro ______ic acid

Ternary acids (H + polyatomic ion): –ate ions: _________ic acid –ite ions: _________ous acid

Name the following acids: HBr H2SO3

H3PO4

Write the formulas for the following acids: Hydrosulfuric acid Nitrous acid Chromic acid

Definition of Bronsted-Lowry Acid

A chemical species that is able to lose or "donate" a hydrogen ion (aka proton because the H+ contains no electrons or neutrons)

Acid loses a hydrogen ion

Properties of Acids

Taste sour Corrosive Feel watery Are electrolytes: conduct an electrical current by

forming H+ ions in solution

pH < 7

Review: Naming a Base

Formula is name + “hydroxide”: Metal + OH-

Ammonium + OH-

Name the following bases: NaOH NH3

Ca(OH)2

Write the formulas for the following bases: Magnesium hydroxide Aluminum hydroxide Lithium hydroxide

Definition of Bronsted-Lowry Base

A chemical species that is able to gain or "accept" a hydrogen ion (aka proton because the H+ contains no electrons or neutrons)

Base gains a hydrogen ion

Properties of Bases

Taste bitter Corrosive Feel slippery Are electrolytes: conduct an electrical current by

forming OH- ions in solution

pH > 7

Indicators

Indicators: organic substances that change colors in an acid or a base (sometimes paper, sometimes liquids)

Acids turn… Litmus paper – red Phenolphthalein – clear Universal indicator – red/orange

Bases turn… Litmus paper – blue Phenolphthalein – pink Universal indicator – blue

Household Items& the pH Scale

pH and pOH Scale

Measured on a numeric scale from 0-14 This scale number indicates ion concentration of a solution

It is much easier to work numbers 0-14 than with than the actual range of 1 to 10–14 (0.00000000000001)

In an acidic solution, [H+] > [OH-] In a basic solution, [H+] < [OH-] pH + pOH = 14

pH pOH

Stands for “power of hydrogen”

Stands for “power of hydroxide”

Shows the [H+] in a solution

Shows the [OH-] in a solution

pH = -log[H+] pOH = -log[OH-]

pH and pOH Scale

[H+] and [OH-] are inverses: the exponents always add up to -14 Ex: If [H+] = 1.0x10-3M, then [OH-] = 1.0x10-11M

pH and pOH Calculations

Notice the relationship between concentration and the pH / pOH value: Toothpaste has a hydrogen ion concentration of

10–10M, so its pH is 10.

pH = -log[10-10] = 10 Pure water, which is neutral, has a pH of 7. That

means its hydrogen ion concentration is 10–7M.

7 = -log[H+] ; [H+] = 10-7

pH & pOH Practice

1. In a NaOH solution the pH = 11. What is the [H+] of the solution?

2. If a substance’s pH = 3, what is the pOH?

3. Find the pH and pOH of a 0.1M HNO3 solution.

n If the [H+] = 1x10-4M, what is the [OH-]? What is the pH and pOH?

11 = -log[H+] ; [H+] = 10-11 M

3 + pOH = 14 ; pOH = 11

pH = -log[0.1] = 1

1 + pOH = 14 ; pOH = 13

1x10-4 + [OH-] = 1x10-14 ; [OH-] = 1x10-10

pH = -log[1x10-4] = 4 & pOH = -log[1x10-10] = 10

(once you get pH, you can just subtract from 14 to get pOH)

Strength of Acids and Bases

Determined by how much they ionize (dissociate) in water

Strong – ionize 100% in water Weak – only partially ionize in water

a) Complete dissociation - all HCl compounds have separated into H+ and Cl- ions

b) Partial dissociation - some HNO2 compounds have separated into H+ and NO2

- ions, while some remain together

Strength of Acids and Bases

The terms weak and strong are used to compare the strengths of acids and bases

The terms dilute and concentrated are used to compare the concentration of solutions

They do not mean the same thing!

The combination of strength and concentration ultimately determines the behavior of the acid or base.

Strength of Acids and Bases

Strong Acids: Only HNO3, HI, HBr, HCl, H2SO4, HClO4

Remember: NO, I Brought Claude SOme ClOthes All other acids are weak, and remain in equilibrium

Ex: HNO2 ↔ H+ + NO2-

Strong Bases: Group I or II metals

Ex: NaOH, Mg(OH)2…etc.

All other bases are weak, and remain in equilibrium Ex: NH3 + H2O ↔ NH4

+ + OH-

Conjugate Acids & Bases

Conjugate acids are formed when a base accepts a proton (H+)

Conjugate bases are formed when an acid donates a proton (H+)

Conjugate Strength

Strong Acid = weak conjugate base Strong Base = weak conjugate acid

Weak Acid = strong conjugate base Weak Base = strong conjugate acid

Example:HCl + NH3 → Cl- + NH4

+

(strong acid) (weak base) (weak conjugate base) (strong conjugate acid)

Conjugate Practice

Label the acid (A), base (B), conjugate acid (CA) & conjugate base (CB).

1. NH3 + HNO3 → NH4+ + NO3

-

2. CH3OH + NH2- → CH3O- + NH3

3. OH- + H3O+ → H2O + H2O

4. NH2- + H2O → NH3 + OH-

B A CA CB

A B CB CA

B A CA CB

B A CA CB

Neutralization

Neutralization: the reaction of an acid and a base; products are salt and water Example: consuming antacid products, which

are basic, neutralizes stomach acid

Neutralization

Example: sodium hydroxide (base) and hydrochloric acid (acid) react to form sodium chloride (salt) and water.

Neutralization Practice

Neutralizations are double displacement reactions!Practice predicting products (always a salt and water):

Example #1__Ca(OH)2 + __H3PO4 → ?

Example #2

__Fe(OH)2 + __HBr → ?

__Ca(OH)2 + __H3PO4 → __Ca3(PO4)2 + __H2O3Ca(OH)2 + 2H3PO4 → Ca3(PO4)2 + 6H2O

__Fe(OH)2 + __HBr → __FeBr2 + __H2O

Fe(OH)2 + 2HBr → FeBr2 + 2H2O

Titration

1. An indicator (phenolphthalein) is added to the standardized acid (acid of known concentration).

2. The unknown base is added until the solution is neutralized and reaches the equivalence point (where [H+] is equal to [OH-]).

3. Adding one more drop of base changes the color of the solution to pink. This is called the endpoint.

* The equivalence point is not necessarily the midpoint, or the point where pH = 7

Titration – determining the concentration of a base by using an acid whose concentration is known.

Titration Calculations

MaVa(#H+) = MbVb(OH-) M = concentration (molarity) V = volume (L or mL) (#H+ or OH-) = number of ions

Example: It took 75mL of NaOH to neutralize 50mL of 2M HCl. What is the concentration of the NaOH?

MaVa(#H+) = MbVb(#OH-)

(2M)(50mL)(1) = (x)(75mL)(1)

x = 1.33M NaOH

Titration Practice

Practice: It took 20mL of Ca(OH)2 to neutralize 25mL of 0.05M HCl. What is the concentration of the base?

MaVa(#H+) = MbVb(#OH-)

(0.05M)(25mL)(1) = (x)(20mL)(2)

x = 0.031 M

Definition of Arrhenius’ Acids & Bases

Acids/bases are determined by what type of ions they produced Arrhenius Acids produce H+ ions in solution

Monoprotic acids – have 1 ionizable hydrogen Diprotic acids – have 2 ionizable hydrogens Triprotic acids – have 3 ionizable hydrogens

Arrhenius Bases produce OH- in solution

Produces H+ ions in solution

Produces OH- ions in solution