Acids and Bases Notes

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. NH 3 )

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 K a 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 K a 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 H 2 S). 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) HNO 3 – nitric from nitrate H 2 SO 4 - sulfuricfrom sulfate HClO 4 - perchloricfrom perchlorate

b. weak acids (acids with l less oxygen than the “ic” ending HNO 2 – nitrousfrom nitrite H 3 PO 3 - phosphorous from phosphite H 2 SO 3 - sulfurousfrom sulfite HClO 2 - chlorousfrom chlorite c. weaker acids (acids with “hypo ous” have less oxygen than the “ous” ending HNO - hyponitrous H 3 PO 2 - hypophosphorus HClO - hypochorous

d. Organic acids – have carboxyl group - COOH - usually weak acids HC 2 H 3 O 2 - acetic acid C 7 H 5 COOH - 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.

AcidsBases Usually 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 H 2 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

AcidsBases Arrhenius Acid: donates (or produces) hydronium ions (H 3 O+) in water or hydrogen ions (H+) in water Bronsted-Lowry Acid: donates a proton (H+) in water, H 3 O+ has an extra H+, if it donated it to another molecule it would be H 2 O HNO 3 + H 2 O  H + + NO 3 - HNO 3 + H 2 O  H 3 O + + NO 3 - HCl + H 2 O  H + + Cl - HCl + H 2 O  H 3 O + + 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 H 2 O KOH + H 2 O  K + + OH - NH 3 + H 2 O  NH OH -

HF + H 2 O  F - + H 3 O + Acid Base Conjugate Conjugate BaseAcid 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, H 3 O + is referred to as the conjugate acid of water. H 3 O + 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 + H 2 O  Cl - + H 3 O + Acid Base Conjugate Conjugate Base Acid H 2 SO 4 + H 2 O  HSO H 3 O + Acid Base Conjugate Conjugate Base Acid NH 3 + H 2 O  OH - + NH 4 + Base AcidConjugate Base Conjugate Acid

2. What is the conjugate base of the following substances? a.H 2 O ________________ b.NH 4 + ________________ c.HNO 2 _______________ d.HC 2 H 3 O 2 _________________ 3. What is the conjugate acid of the following substances? a.HCO 3 - __________________ b.H 2 O____________ c.HPO 4 2- ____________ d.NH 3 ___________

III. Water Water is a substance that can act as an acid or as a base. Autoionization of water: H 2 O + H 2 O  H 3 O + + OH -

Ionization constant for water (K w ) K w = [H ][OH - ] or K w = [H + ][OH - ] Because in water at 25°C [H + ] = l.0 X l0 -7 M and [OH - ] = l.0 X l0 -7 M the K w = 1.0 X l0 -14 mol 2 /L 2 No matter what an aqueous solution contains at 25°C [H + ] [OH - ] = l.0 x l0 -14 mol 2 /L 2 K w varies with temperature. Neutral solution [H+] = [OH-] Acidic solution [H+] > [OH-] Basic solution [H+] < [OH-]

K w Problems: If the molarity of a strong acidic or basic is known we can use the Kw to find the [H+] or [OH-]. K w = [H + ][OH - ] or l.0 x l0 -14 mol 2 /L 2 = [H + ] [OH - ] 1. Determine the hydrogen ion and hydroxide ion concentrations in a solution that is 3.0X10 -2 M NaOH. l.0 x l0 -14 mol 2 /L 2 = [H + ] [OH - ] l.0 x l0 -14 mol 2 /L 2 = [H + ] [3.0X10 -2 ]

K w Problems: If the molarity of a strong acidic or basic is known we can use the Kw to find the [H+] or [OH-]. K w = [H + ][OH - ] or l.0 x l0 -14 mol 2 /L 2 = [H + ] [OH - ] 2. Determine the hydrogen ion and hydroxide ion concentrations in a solution that is 4.0X10 -3 M HNO 3.

IV. pH Scale [ ] brackets mean concentration or Molarity 1. The pH scale indicates the hydronium ion concentration, [H 3 O + ] or molarity, of a solution. (In other words how many H 3 O + 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… …15 Acidic Basic [H 3 O + ] A lot of H 3 O + Not a lot of H 3 O + Acidic Basic

pOH Scale 2. 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… …15 Basic Acidic [OH - ] A lot of OH - Not a lot of OH - Basic Acidic

Example: 1.Lemon juice (citric acid) pH = 2.0, pOH = Pure water pH = 7.0, pOH = 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 And now shake it a bit.

3. Calculations Involving pH, pOH, [H 3 O+], and [OH-] of strong Acids and Bases 1 st: determine which ion will be produced, either OH or H 3 O+ (Acids produce H 3 O+ and bases produce OH-). 2 nd: use formula to determine pH or pOH. 3 rd: check to see if answer is reasonable. pH = -log [H 3 O + ]OR pH = -log [H + ] pOH = -log [OH - ] pOH + pH = 14

Example Problems: 1. What is the pH of a 0.001M NaOH solution? 1 st step: Hydroxide will be produced and the [OH - ] = 0.001M 2 nd step: pOH = -log [0.001] pOH = 3.0 pH = = 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 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 -5 M 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 grams of KOH were used to prepare the solution? 5. What is the pOH of a 1.1X10 -5 M HNO 3 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 [H 3 O + ] is less than 1.0X10 -7, the water becomes the important source of [H 3 O + ] or [H + ] and the pH is Just remember to check if you answer is reasonable! 7. What is the pH of a 2.5X M HCl solution? 8. What is the pH of a 1.0X M HNO 3 solution?

Now complete Acids and Bases Worksheet #1

4. K a and K b and Calculations Involving pH of Weak Acids and Weak Bases A. K a and Weak acids - Very little of a weak acid ionizes. Most of it stays in its molecular form: HC 2 H 3 O 2 + H 2 0 = H C 2 H 3 O 2 - Continue on overhead.