ACIDS & BASES

ACID/BASE THEORY Acids and bases are solutions which can be described differently by multiple theories. So far, we have treated everything that utilizes “H” as a cation = acid H 3 PO 4 “OH” as an anion = base NaOH

ARRHENIUS THEORY The theory that anything capable of producing H + ions are acids and those producing OH - anions are bases is Arrhenius’ Theory of acids/bases. Based on the notion that these substances dissociate in solution into their ions. H 2 SO 4 2H + + SO 4 -2 H20H20

ACID OR BASE? HNO 3 KOH AcidBase Ca(OH) 2 HBr BaseAcid HC 2 H 3 O 2 Al(OH) 3 AcidBase

BRONSTAD LOWRY ACIDS/BASES More general description of acids and bases, incorporates all Arrhenius acid/bases Acids = H + donors Bases = H + acceptors Example: NH 3 (aq) + H 2 O (l) NH 4 + (aq) + OH - (aq) Would solutions of NH 3 be acidic or basic?

CONJUGATE ACIDS/BASES NH 3 (aq) + H 2 O (l) NH 4 + (aq) + OH - (aq) Conjugate Acid: The compound remaining after H + acceptance by a base. NH 3 NH 4 + Base Conjugate Acid Conjugate Base: The compound remaining after H + donation by an acid. H 2 O OH - Acid Conjugate Base

LEWIS ACID/BASES Describes Acid/Bases based upon electron donation. Lewis Acid: A substance that can accept a pair of electrons to form a covalent bond. Lewis Base: A substance that can donate a pair of electrons to form a covalent bond. H + + OH - H 2 O

STRENGTH OF ACIDS/BASES For this class, we will mostly discuss Arrhenius acid/bases (H + cation/OH - anion) The strength of these solutions is determined by the concentration (Molarity) of H + or OH - ions in the solution. Dependent upon… 1) Amount of dissolved solute donating the ion 2) Likelihood of ion dissociation

CONCENTRATION OF SOLUTE Just like calculating the molarity of non acid/base solutions. M = mol solute / liter solution Example: What is the concentration of a H 2 SO 4 solution if 13.2 g of solute are dissolved in 100mL of di-water?

CALCULATING [ H + ] & [OH - ] However, we cannot assume the molarity (concentration) of H + /OH - ions is the same as the molarity of the solution for 2 reasons: 1.Not all acids/bases completely dissociate into their ions. 2.Not all acidic/basic compounds donate 1 ion per molecule

Complete dissociation: all solute dissociates into ions, meaning the concentration of ions can be calculated with the molar ratio. HClH + + Cl - 1 mol HCl produces 1 mol H + So a 0.2M HCl solution would have a H + concentration of 0.2M as well DISSOCIATION

COMPLETE DISSOCIATION Few acids/bases completely dissociate If they do, they are termed “Strong Acids/Bases” because they produce high concentrations of their ions upon dissociation. Strong Acids (7): HCl, HBr, HI, H 2 SO 4, HNO 3, HClO 3, HClO 4 Strong Bases (8): LiOH, NaOH, KOH, RbOH, CsOH, Ca(OH) 2, Sr(OH) 2, Ba(OH) 2

CALCULATING ION DONATION Not all acids/bases donate 1 H + or OH - into solution when they dissociate! How many ions would the following acids/bases donate if they completely dissociate? HBr Ca(OH) 2 H 2 SO 4

[H+] EXAMPLE Using the previous H 2 SO 4 example (13.2 g of solute are dissolved in 100mL of di- water), calculate the [H 3 O + ] of the solution.

PARTIAL DISSOCIATION Weak acids/bases do not completely dissociate in water. They are called weak, because a lower concentration of H + or OH - ions results. Example: Only about 1% of Phosphoric Acid (H 3 PO 4 ) dissociates into H + + H 2 PO 4.

DISSOCIATION OF STRONG & WEAK ACIDS/BASES In other words, you would need to know what percentage of an acidic/basic compound is likely to donate its ions into solution in order to calculate the [H + ] & [OH - ]. For this class, we will be working with strong acids/bases. So complete dissociation (ion donation) can be assumed.

POTENTIAL OF HYDROGEN pH = potential of hydrogen pH is an expression of the concentration of H + ions in solution. Since H + readily reacts with water to form H 3 O +, we calculate… pH = −log [H 3 O + ] [H 3 O + ] = 10 -pH

PH & POH Just as pH is an expression of the concentration of H + ions in solution, pOH expresses the concentration of OH- ions in solution… pOH = −log [OH - ] [OH - ] = 10 -pOH pH & pOH always add up to 14 and thus are related through the equation: pH + pOH = 14

PH SCALE pH < 7 acidic pH = 7 neutral pH > 7 basic High [H 3 O + ] acid Low [H 3 O + ] base [H 3 O + ] = ~1x10 -7 neutral

ACID/BASE REACTIONS Also known as neutralization reactions, because the pH of the final solution becomes neutralized towards pH=7 Either [H 3 O + ] or [OH - ] is decreased by forming more neutral products. Acid + Base Salt + Water

ACID/BASE REACTIONS 2 Types you will need to know… 1) Acid + Base Salt + H 2 O 2) Acid + Carbonate Salt + H 2 O + CO 2

ACID/BASE REACTION #1 Example: Hydrochloric acid reacts with sodium hydroxide. HCl(aq) + NaOH(aq) NaCl(aq) + H 2 O(l)

ACID/BASE REACTION #2 Example: Potassium carbonate reacts with sulfuric acid. H 2 SO 4 (aq)+ K 2 CO 3 (aq) K 2 SO 4 (aq) + H 2 O(l) + CO 2 (g) Acid Carbonate Salt Water Carbon Dioxide