Intro to Acids and Bases (again!)

Anion (example) Acid (example) _______ ide (chloride, Cl - ) ________ate (chlorate, ClO 3 - ) _________ite (chlorite, ClO 2 - ) hydro____ic acid (hydrochloric acid, HCl) _______ic acid (chloric acid, HClO 3 ) _______ous acid (chlorous acid, HClO 2 ) Add H + Naming acids An acid is loosely defined as a compound that produces hydrogen ions (H + ) when dissolved in water Acids are named depending on the anion in the compound

AcidAnion rootName H 2 SO 4 SulfateSulfuric acid H 3 PO 4 PhosphatePhosphoric acid HClChlorideHydrochloric acid HC 2 H 3 O 2 AcetateAcetic acid HNO 3 NitrateNitric acid HClO 2 ChloriteChlorous acid HClO Hypochlorite Hypochlorous acid

Writing Formulas Acids Acid NameFormulaAnion Name Acetic acidHC 2 H 3 O 2 acetate Carbonic acidH 2 CO 3 carbonate Hydrochloric acidHClChloride Nitric acidHNO 3 Nitrate Phosphoric acidH 3 PO 4 Phosphate Sulfuric acidH 2 SO 4 Sulfate

Names and formulas for Bases  A base is a compound that produces hydroxide ions (OH - ) when dissolved in water  Bases are named in the same way as other ionic compounds—the name of the cation is followed by the name of the anion  Examples - Sodium hydroxide (NaOH); potassium hydroxide (KOH)

Strengths of Acids and Bases  The strength of an acid/base depends on how well the ions dissociate  Influenced by  Polarity (more polar = stronger)  Bond strength (Stronger bonds = weaker acid/bases because they don’t dissociate)  Stability of anion (more stable = stronger)  Strong ≠ high concentration  Strength measures the degree of separation  Concentration refers to how many particles are present

Strength of Acids/Bases  Strong acids/bases – completely dissociate, strong electrolytes  Examples you should know: HNO 3, H 2 SO 4, HCl, HBr, HI; KOH, NaOH  Weak acids/bases – don’t completely dissociate and are weak electrolytes  Generally, organic acids like acetic acid (vinegar)  Not many weak bases; i.e. NH 3

Defining Acids and Bases  Multiple ways to define acids and bases  Arrhenius acids/bases  Acids are hydrogen-containing compounds that yield hydrogen ions (H + ) in aqueous solution  Bases yield hydroxide ions (OH - ) in aqueous solution

Arrhenius Acids  H + is also known as a proton  Acids can be monoprotic, diprotic, or triprotic  Monoprotic: HNO 3 → H + + NO 3 -  Ionization yields one hydrogen ion  Diprotic: H 2 SO 4 → 2H + + SO 4 2-  Complete ionization yields 2 hydrogen ions  Triprotic: H 3 PO 4 → 3H + + PO 4 3-  Complete ionization yields 3 hydrogen ions

Arrhenius Acids  Not all the hydrogens in an acid may be released as hydrogen ions  Not all hydrogen-containing compounds are acids  Only hydrogens joined to very electronegative elements with very polar bonds, are ionizable in water H H H H+H+ CCO-O- O Ethanoic Acid Nonionizable Hydrogen Ionizable Hydrogen

Arrhenius Bases  Bases formed with group one metals are very soluble and caustic  NaOH → Na + (aq) + OH - (aq)  KOH → K + (aq) + OH - (aq)  Bases of group 2 metals are very weak  Examples are Ca(OH) 2 and Mg(OH) 2

Bronsted-Lowry Acids and Bases  Arrhenius definition is not very comprehensive  Ammonia (NH 3 ) is a base, but there is no hydroxide (OH - ) in the compound to ionize  The Bronsted-Lowry theory defines an acid as a hydrogen-ion donor, and a base as a hydrogen-ion acceptor NH 3 (aq) + H 2 O(l) → NH 4 + (aq) + OH - (aq) Hydrogen ion aceptor, Bronsted-Lowry Base Hydrogen ion donor, Bronsted-Lowry Acid Makes the solution basic

Conjugate Acids and Bases  A conjugate acid is the particle formed when a base gains a hydrogen ion  A conjugate base is the particle that remains when an acid has donated a hydrogen ion  A conjugate acid-base pair consists of two substances related by the loss or gain of a single hydrogen ion  Acids have conjugate bases while bases have conjugate acids NH 3 (aq) + H 2 O(l) NH 4 + (aq) + OH - (aq) BaseAcid Conjugate Acid Conjugate Base conjugate acid-base pair

HCl(aq) + H 2 O(l) H 3 O + (aq) + Cl - (aq) AcidBase Conjugate Acid Conjugate Base conjugate acid-base pair  A water molecule that gains a hydrogen ion becomes a positively charged hydronium ion H 3 O +  Water can both accept AND donate a hydrogen ion  A substance that can act as both an acid and a base is said to be amphoteric  Amino Acids as an example – building block of protein

Lewis Acids and Bases  Acids accept a pair of electrons during a reaction while a base donates a pair of electrons  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  MUCH broader, more inclusive definition than any of the others NH 3 + BF 3 → NH 3 BF 3 Identify the Lewis Acid and the Lewis Base in the above equation

H + + H 2 O → H 3 O + H+H+ Acid Base

Acid-Base Definitions Review TypeAcidBase ArrheniusH + producerOH - producer Bronsted-LowryH + donorH + acceptor Lewiselectron-pair acceptorelectron-pair donor

Reactions of Acids/Bases (Arrhenius and B.L kinds)  Single replacement  Double replacement

Single Replacement Reactions  A + BC = AB + C  A chemical change in which one element replaces a second element in a compound  Acids react strongly with most metals – reactivity with metals used to be a common way to classify acids  Hydrogen from the acid is always the cation replaced by the metal  Examples: 2K(s) + 2H 2 O(l)  2KOH(aq) + H 2 (g) 2Al (s) + 6HNO 3 (aq)  2Al(NO 3 ) 3 (aq) + 3H 2 (g)

Activity Series of Metals  Notice that aluminum is higher on the activity series of metals than hydrogen  A reactive metal will replace any metal listed below it in the activity series 2Al (s) + 6HNO 3 (aq)  2Al(NO 3 ) 3 (aq) + 3H 2 (g) Cu + HNO 3  No reaction Decreasing reactivity Single Replacement Reactions

2K(s) + 2H 2 O(l)  2KOH(aq) + H 2 (g) 2Al (s) + 6HNO 3 (aq)  2Al(NO 3 ) 3 (aq) + 3H 2 (g) Ca (s) + H 2 SO 4 (aq)  CaSO 4 + H 2 (g) Pt (s) + HCl (aq)  N.R. 2Na (s) + H 2 SO 4 (aq)  Na 2 SO 4 + H 2 (g) Practice Problems

Double Replacement Reactions  AB + CD = AC + BD  The ions of two compounds exchange places in an aqueous solution to form two new compounds  Often produce a precipitate, a gas, or molecular compound such as water  Precipitation (forms a solid or gas as a product)  Acid/Base (forms water as product); also known as a neutralization reaction  Ca(OH) 2 (aq) + 2HCl(aq)  CaCl 2 (aq) + 2H 2 O(l)

Reactions in Aqueous Solution Acid-Base reactions  Acids and bases react to form water and a salt, a generic name for an ionic compound H 3 PO 4 + 3Fe(OH) 2  Fe 3 (PO 4 ) 2 + 6H 2 O H 2 SO 4 + Ca(OH) 2  CaSO 4 + 2H 2 O