Acids and Bases

Acids and Bases

Properties of Acids (in aq solution)

1. Sour taste

2. Low pH

3. Turn litmus paper red

4. Conduct electrical current

Properties of Bases (in aq solution)

1. Bitter taste2. Slippery3. High pH4. Turn litmus paper blue5. Conduct electrical

current

Arrhenius Definition

Acid = substance that releases H+ ions in aq solutionHCl H+ + Cl-

Base = substance that releases OH- ions in aq solutionNaOH Na+ + OH-

Acid-Base Reactions

• Known as a neutralization reaction. Acids and bases will react with each other to form salt and water.

HCl + NaOH NaCl + H2O

Bronsted-Lowry Definition

As more and more substances were determined to have acidic or basic properties, even some without obvious H+ or OH-, a new definition was needed.

• Acid = proton donor

• Base = proton acceptor

Bronsted-Lowry Definition

• Acid = proton donor

H2O + HCl H3O+ + Cl-

Bronsted-Lowry Definition

• Base = proton acceptor

NH3 + H2O NH4+ + OH–

• Lewis Acid – something that accepts an electron pair to form a covalent bond

• Lewis Base – something that donates an electron pair to form a covalent bond

A + :B → A—B

Acids & Bases Review

• Acid– substance that releases H+ ions in aq solution– Proton donor– Electron pair acceptor

• Base– substance that releases OH- ions in aq

solution– Proton acceptor– Electron pair donator

Conjugate Acid-Base Pairs

• In an acid-base reaction, and acid plus a base reacts to form a conjugate base plus a conjugate acid

Acid + Base Conjugate Base + Conjugate Acid

• The conjugate acid of a base is formed when the base gains a proton. A conjugate base is formed when an acid loses a proton.

NH3 + H20 NH4+ + OH-

Proton Acceptor = Base

Proton Donor = Acid

Additional Proton means it is now a Proton Donor = Conjugate Acid

Loss of proton means it is now a Proton Acceptor = Conjugate Base

Note:• The conjugate name only refers to acids and bases in the PRODUCTS• Conjugate pairs differ only by a proton• NH3 and NH4

+ are a conjugate acid-base pair• H20 and OH- are a conjugate acid-base pair • A strong acid becomes a weak conj. base (and vice versa)

Acid & Base Naming

• Bases are named exactly the same

• Ex. Ca(OH)2 is Calcium hydroxide

Acid Naming OverviewBinaryStart with hydro-ElementEnd with –ic acid

Tertiary (Oxyacids)“I ate something, and now I am sick”If anion ends in –ate then the acid ends in –

icIf the anion ends in –ite then the acid ends

in -ous

• Naming WS

Acid Strength

A stronger acid will transfer MORE protons (H+) than a weak acid. It will create more hydronium ions (H3O+) in water.

Hydrochloric acid

HCl + H2O H3O+ + Cl-

Acetic Acid

CH3COOH + H2O H3O+ + CH3COO-

More dissociation!

Less dissociation!

How do we compare the strength of an acid or a base?

We measure the amount of hydronium ions they create (acids) or the amount of hydroxide ions they create (bases)….using concentration.

• When water gains a proton it is called HYDRONIUM!!

H3O+

• When water loses a proton it is called HYDROXIDE!!

OH-

What is concentration?

• Using molarity, it is a measure of moles of solute in liters of solution.

• Concentration is measured in WATER!

H2O is both an acid and a base

Water is simultaneously donating and accepting protons!

What are the ion concentrations in water?

• The concentrations of H3O+ and OH- in pure water are each 1.0×10-7 mol/L at 25ºC.

• Putting a symbol in brackets is used to signify the concentration.

• [H30+] = 1.0×10-7 M

• [OH-] = 1.0×10-7 M

Ionization Constant of water, KW

• KW = [H30+] [OH-]

• KW = (1.0×10-7)(1.0×10-7)

= 1.0×10-14

• Acids increase the [H30+] Whenever [H30+] is greater than [OH-], the solution is acidic.

• Bases increase the [OH-]

Whenever [OH-] is greater than [H30+], the solution is basic.

With an increase in [H30+], some of the H30+ ions will react with the OH- ions, reducing [OH-] . [H30+][OH-] will still = 1.0x10-14

• Concentration values tend to be small…so we use a more convenient scale. pH!

pH + pOH = 14

• pH – A measure of the acidity of a solution.

• It is the negative logarithm of the hydronium ion [H30+] concentration.

pH = -log [H30+]

pH + pOH = 14

• pOH – A measure of how basic a solution is.

• It is the negative logarithm of the hydroxide [OH-] concentration.

pOH = -log [OH-]

• The logarithm scale is created to make numbers over a large range more manageable.

• The logarithm base 10 of a number x is the power to which 10 must be raised in order to equal x.

• Log 10 x = ? Log 100 = ?

• 10? = x 10 ? = 100

• Remember, our concentrations are SMALL. So we are going to be dealing with decimals…

• Log 10 x = ? Log .001 = ?

• 10? = x 10 ? = .001

[H+] = 1×10-3 = 0.001

pH = -log [H+]

pH = -log (1×10-3)

pH = 3

To determine pH from a concentration where 1 is the only digit, write the concentration in scientific notation. The absolute power of the exponent will be the pH.

• For a base, you do the same thing except remember that you are solving for pOH first…

Ionization Constant of water, KW

• KW = [H30+] [OH-]

• KW = (1.0×10-7)(1.0×10-7)

= 1.0×10-14

Solutions [H+] pH [OH-] pOH

1.0×10-3M HClO4

0.010 M HCl

0.000001 M KOH

6.00×10-4 HBr

0.20 M NaOH

0.00300 H2SO4

1.0×10-3M 1.0×10-11M3.0 11

1.0×10-2M 1.0×10-12M2.0 12

1×10-8M 1×10-6M8 6

6.00×10-4M 1.67×10-11M3.22 10.8

5.0×10-14M 2.0×10-1M13 .70

6.00×10-3M 1.67×10-12M2.22 11.8

Equations to Know!!

• [H30+] [OH-] = 1.0×10-14 M

• pH + pOH = 14

• pH = -log [H30+]

• pOH = -log [OH-]

• [H30+] = 10-pH

• [OH-] = 10-pOH

Green Workbook

• Pg. 262 #2

• Pg. 264 #1

• Pg. 267 #3

• Pg. 269 #1 & #2

• Pg. 270 #7