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Acids and Bases. Properties of Acids (in aq solution). Sour taste Low pH Turn litmus paper red Conduct electrical current. Properties of Bases (in aq solution). Bitter taste Slippery High pH Turn litmus paper blue Conduct electrical current. Arrhenius Definition.
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Properties of Acids (in aq solution) • Sour taste • Low pH • Turn litmus paper red • Conduct electrical current
Properties of Bases (in aq solution) • Bitter taste • Slippery • High pH • Turn litmus paper blue • Conduct electrical current
Arrhenius Definition Acid = substance that releases H+ ions in aq solution HCl H+ + Cl- Base = substance that releases OH-ions in aq solution NaOH 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- Additional Proton means it is now a Proton Donor = Conjugate Acid Loss of proton means it is now a Proton Acceptor = Conjugate Base Proton Acceptor = Base Proton Donor = Acid • 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 Overview Binary Start with hydro- Element End with –ic acid Tertiary (Oxyacids) “I ate something, and now I am sick” If anion ends in –ate then the acid ends in –ic If the anion ends in –ite then the acid ends in -ous
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.
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
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 • 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.
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
11 3.0 1.0×10-3M 1.0×10-11M 2.0 12 1.0×10-2M 1.0×10-12M 8 6 1×10-8M 1×10-6M 10.8 3.22 6.00×10-4M 1.67×10-11M 13 .70 2.0×10-1M 5.0×10-14M 2.22 11.8 6.00×10-3M 1.67×10-12M
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