Acids and Bases Notes

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I. Strength of Acids and Bases A. Bases:

Strong Bases: metal hydroxides of Group I and II metals (except Be) that are soluble in water and dissociate (separates into ions) completely in dilute aqueous solutions

Weak Bases: a molecular substance that ionizes only slightly in water to produce an alkaline (basic) solution (ex. NH3)

My uncle was a chemist, a chemist he's no more for what he thought was H 2 O was

H 2 S O 4. (Ha Ha)B. Acids:

Strong Acids: an acid that ionizes (separates into ions) completely or very nearly completely in aqueous solutions (will not have an ionization constant (Ka) value and will not be on Ka chart).

Weak Acids: an acid that ionizes only slightly in dilute aqueous solutions (will have an ionization constant (Ka) value) and will be on the Ka chart).

Why do white bears dissolve in water? Because they're polar.

1. Binary or hydrohalic acids – HCl, HBr, and HI “hydro____ic acid” are strong acids. Other binary acids are weak acids (HF and H2S). Although the H-F bond is very polar, the bond is so strong (due to the small F atom) that the acid does not completely ionize.

2. Oxyacids – contain a polyatomic ion

a. strong acids (contain 2 or more oxygen per hydrogen)

HNO3 – nitric from nitrate

H2SO4 - sulfuric from sulfate

HClO4 - perchloric from perchlorate

b. weak acids (acids with l less oxygen than the “ic” ending

HNO2 – nitrous from nitrite

H3PO3 - phosphorous from phosphite

H2SO3 - sulfurous from sulfite

HClO2 - chlorous from chlorite

c. weaker acids (acids with “hypo ous” have less oxygen than the “ous” ending

HNO - hyponitrous

H3PO2 - hypophosphorus

HClO - hypochorous 

d. Organic acids – have carboxyl group -COOH - usually weak acids

HC2H3O2 - acetic acid

C7H5COOH - benzoic acid

Q: What's the most important thing to learn in chemistry?

A: Never lick the spoon (Ha Ha)II. Characteristics of Acids and Bases

There are multiple definitions for acids and bases and I have summarized them all here. Keep in mind that there are some exceptions and this is just a guide to follow when trying to determine if a substance is an acid or a base.

Acids BasesUsually begin with H

Sour taste

Litmus paper turns red

pH paper 1-6 or pH meter

Phenolphthalein - colorless

Feels like water

React with metals to produce H2

Electrolyte

pH<7

Usually contain OH

Bitter taste

Litmus paper turns blue

pH paper 8-14 or pH meter

Phenolphthalein – pink

Feels slippery

Electrolyte

pH>7

Acids BasesArrhenius Acid: donates (or

produces) hydronium ions (H3O+) in water or hydrogen ions (H+) in water

Bronsted-Lowry Acid: donates a proton (H+) in water, H3O+ has an extra H+, if it donated it to another molecule it would be H2O

HNO3 + H2O H+ + NO3- 

HNO3 + H2O H3O+ + NO3

-  

HCl + H2O H+ + Cl-

HCl + H2O H3O+ + Cl-

 

Arrhenius Base: donates (or produces) hydroxide ions (OH-) in water

Bronsted – Lowry Base: accepts a proton in water, OH- needs an extra H+ if it accepts one from another molecule it would be H2O

KOH + H2O K+ + OH-

NH3 + H2O NH4+ + OH-

HF + H2O F - + H3O+

Acid Base Conjugate Conjugate Base Acid

Here HF donated a proton (H+) to the water and the water accepted the proton (H+).

HF is referred to as the acid and water is referred to as the base.

The fluorine ion, F- is referred to as the conjugate base of HF. F- can accept a proton (H+) to be stable.

The hydronium ion, H3O+ is referred to as the conjugate

acid of water. H3O+ can donate a proton (H+) to be

stable.

Conjugates:

Example: Determine the acid, base, conjugate acid, and conjugate base in each of the

following equations:HCl + H2O Cl- + H3O

+ Acid Base Conjugate Conjugate   Base Acid

 H2SO4 + H2O HSO4- + H3O

+

Acid Base Conjugate Conjugate   Base Acid

 NH3 + H2O OH- + NH4+

Base Acid Conjugate Base Conjugate Acid

2. What is the conjugate base of the following substances?

a. H2O ________________

b. NH4+________________

c. HNO2_______________

d. HC2H3O2_________________ 3. What is the conjugate acid of the following

substances?

a. HCO3-__________________

b. H2O____________

c. HPO42-____________

d. NH3___________

III. WaterWater is a substance that can act as an acid or as a base. Autoionization of water:

H2O + H2O H3O+ + OH-

Ionization constant for water (Kw) Kw = [H30

+][OH-] or Kw = [H+][OH-]Because in water at 25°C [H+] = l.0 X l0-7 M and [OH-] = l.0 X l0-7 M

the Kw = 1.0 X l0-14 mol2/L2 No matter what an aqueous solution contains at

25°C [H+] [OH-] = l.0 x l0-14 mol2/L2

Kw varies with temperature. Neutral solution [H+] = [OH-]

Acidic solution [H+] > [OH-] Basic solution [H+] < [OH-]

Kw Problems: If the molarity of a strong acidic or basic is known we can use the Kw to find the [H+] or [OH-].

Kw = [H+][OH-] or

l.0 x l0-14 mol2/L2 = [H+] [OH-]

1. Determine the hydrogen ion and hydroxide ion concentrations in a solution that is 3.0X10-2M NaOH.

l.0 x l0-14 mol2/L2 = [H+] [OH-]

l.0 x l0-14 mol2/L2 = [H+] [3.0X10-2]

Kw Problems: If the molarity of a strong acidic or basic is known we can use the Kw to find the [H+] or [OH-].

Kw = [H+][OH-] or

l.0 x l0-14 mol2/L2 = [H+] [OH-]

2. Determine the hydrogen ion and hydroxide ion concentrations in a solution that is 4.0X10-3M HNO3.

IV. pH Scale [ ] brackets mean concentration or Molarity

1. The pH scale indicates the hydronium ion concentration, [H3O

+] or molarity, of a solution. (In other words how many H3O

+ ions are in a solution. If there are a lot we assume it is an acid, if there are very few it is a base.)

Q: How do you make a 24-molar solution? A: Put your artificial teeth in water.

Where does the pH scale come from?

pH scale-1…0 1 2 3 4 5 6 7 8 9 10 11 12 13 14…15

Acidic Basic

[H3O+]

1 0.1 0.01 10-3 10-4 10-5 10-6 10-7 10-8 10-9 10-10 10-11 10-12 10-13 10-14

A lot of H3O+ Not a lot of H3O

+

Acidic Basic

pOH Scale2. The pOH scale indicates the hydroxide ion

concentration, [OH-] or molarity, of a solution. (In other words how many OH- ions are in the solution. If there are a lot we assume it is a base, if there are very few it is an acid.)Two chemists meet for the first time at a symposium. One is American, one is British. The British chemist asks the American chemist, "So what do you do for research?" The American responds, "Oh, I work with aerosols." The British chemist responds, "Yes, sometimes my colleagues get on my nerves also."

pOH scale-1…0 1 2 3 4 5 6 7 8 9 10 11 12 13 14…15

Basic Acidic

[OH-]1 0.1 0.01 10-3 10-4 10-5 10-6 10-7 10-8 10-9 10-10 10-11 10-12 10-13 10-14

A lot of OH- Not a lot of OH-

Basic Acidic

Example:1. Lemon juice (citric acid) pH = 2.0, pOH = 12.0

2. Pure water pH = 7.0, pOH = 7.0

3. Milk of magnesia pH = 10.0, pOH = 4.0

The last words of a chemist:

1. And now for the taste test.

2. I wonder if this is hot?

3. And now a little bit from this...

4. And now shake it a bit.

3. Calculations Involving pH, pOH, [H3O+], and [OH-] of strong Acids and Bases

1st: determine which ion will be produced, either OH or H3O+ (Acids produce H3O+ and bases produce OH-). 2nd: use formula to determine pH or pOH. 3rd: check to see if answer is reasonable.

pH = -log [H3O+] OR pH = -log [H+]

pOH = -log [OH-]

pOH + pH = 14

Example Problems:1.      What is the pH of a 0.001M NaOH

solution?

1st step: Hydroxide will be produced and the [OH-] = 0.001M

2nd step: pOH = -log [0.001]

pOH = 3.0

pH = 14.0-3.0 = 11.0

(Significant figures and pH: When conuting significant figures, only count what comes APTER the decimal in a pH or pOH value. For example the number of sig figs in a pH of 12.01 is 2, the number of sig figs in a pH of 12.0 is 1. This is only for pH and pOH values!!!)

Joke

The answer to the problem was "log(1+x)". A student copied the answer from the good student next to him, but didn't want to make it obvious that he was cheating, so he changed the answer slightly, to "timber(1+x)."

2. What is the pH of a 3.4X10-5M HCl solution?

3. What is the pH of a solution if the pOH = 5?

4. What is the pH of a 10 liter KOH solution if 5.611 grams of KOH were used to prepare the solution?

5. What is the pOH of a 1.1X10-5M HNO3 solution?

6. If the pH of a KOH solution is 10.75, what is the molar concentration of the solution? What is the pOH? What is the [H+]?

The pH of a strong acid cannot be greater than 7. If the acid concentration [H3O

+] is less than 1.0X10-

7, the water becomes the important source of [H3O+]

or [H+] and the pH is 7.00. Just remember to check if you answer is reasonable!

7.      What is the pH of a 2.5X10-10M HCl solution?  

8.      What is the pH of a 1.0X10-11M HNO3 solution?

Now complete Acids and Bases Worksheet #1

4. Ka and Kb and Calculations

Involving pH of Weak Acids and Weak Bases

A. Ka and Weak acids - Very little of a weak

acid ionizes. Most of it stays in its molecular form:

HC2H3O2 + H20 = H30+ + C2H3O2

-

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