A CIDS AND B ASES Chapter 15

O BJECTIVES Identify key terms and concepts. Identify an acid and a base using Bronstead- Lowery Acid/Base Theory. Identify a Lewis acid and base. Explain the acid-base properties of water. Name acids and bases. Explain the properties of acids, bases, and salts. Explain how a buffer works. Identify acid-base conjugate pairs. Determine the products of a neutralization reaction.

O BJECTIVES Calculate the pH and hydronium concentration of a solution. Calculate acid/base ionization constants. Determine the percent ionization for an acid or a base. Explain how a salt will affect the pH of a solution. Identify the acid-base properties of an oxide and hydroxide. Determine the relative strength of an acid-base conjugate pair.

A CIDS Cause litmus paper to turn red Tastes sour Dissolves metals like Zn and Fe to produce hydrogen gas

A CIDS For an acid containing a hydrogen and an anion: use the prefix hydro and change the –ide of the nonmetal to –ic and add the word acid. HCl = Hydrogen Chloride is Hydro chloric Acid For an acid containing a polyatomic ion, name the anion after the polyatomic ion, changing the –ate to –ic or the –ite to –ous and add the word acid. HNO 3 = Hydrogen Nitrate is Nitr ic Acid HNO 2 = Hydrogen Nitrite is Nitr ous Acid

W RITE THE N AME OR F ORMULA FOR EACH OF THE F OLLOWING A CIDS H 2 SO 4 HF HCl HBr H 3 PO 4 Acetic acid Carbonic Acid Phosphoric Acid Hydroiodic Acid Phosphorous Acid

A CIDS Strong Acids Strong electrolytes that will completely ionize in water H 2 SO 4  H + + HSO 4 - Only a few strong acids HCl, HNO 3, H 2 SO 4, HBr, HI, HClO 4 Weak Acids Will only partially ionize in water (weak electrolytes) Most acids are weak HF, acetic acid, citric acid, salicylic acid, oxalic acid HF + H 2 O ↔ F - + H 3 O +

B ASES Cause litmus paper to turn blue Tastes bitter Name like a normal compound Ca(OH) 2  Calcium Hydroxide NaOH  Sodium Hydroxide

B ASES Strong Bases Strong electrolytes that will completely ionize in water NaOH  Na + + OH - The hydroxides of Group I & II metals are considered to be strong bases Weak Bases Weak Bases do not furnish OH - ions by dissociation. Instead, they react with water to generate OH - ions. Weak electrolytes NH 3 + H 2 O ↔ NH 4 + OH -

Acids Bases

A CID -B ASE I NDICATORS pH meters Litmus and pH paper Universal Indicator Phenolphthalein Methyl Red Thymol Blue

T HE A RRHENIUS T HEORY Acid A substance that ionizes into hydrogen ions and anions in water HCl  H + + Cl - Base A substance that releases hydroxide ions in water NaOH  Na + + OH - Stated the reaction of an acid and a base will produce salt and water HCl + NaOH  NaCl + H 2 O

P ROBLEMS WITH THE A RRHENIUS T HEORY A hydrogen ion does not exist in water. Instead, the H + ion attaches to one of the oxygen loan pairs of electrons on water to make a hydronium ion. Does not explain the basicity of ammonia of where the hydroxide ion comes from when ammonia is dissolved in an aqueous solution. NH 3 + H 2 O  NH 4 + OH - Applies only to reactions in aqueous solution (water).

B RONSTEAD -L OWRY A CID -B ASE T HEORY Acid Proton Donor HCl + H 2 O  H 3 O + + Cl - Base Proton Acceptor NH 3 + H 2 O  NH 4 + OH -

I DENTIFY THE ACID AND BASE IN THE FOLLOWING REACTIONS USING B RONSTEAD - L OWERY A CID /B ASE T HEORY S 2- + H 2 O  OH - + HS - PO HNO 3  NO HPO 4 2- C 2 O HC 2 H 3 O 2  HC 2 O C 2 H 3 O 2 - HCO 2 H + OH -  CO 2 H - + H 2 O HCl + H 2 O  H 3 O + Cl -

L EWIS A CIDS AND B ASES Lewis Acid Accepts a pair of electrons Lewis Base Donates a pair of electrons Much more general description of acids and bases The reaction does not have to involve the transfer of a hydrogen.

I DENTIFY THE ACID AND BASE IN THE FOLLOWING REACTIONS USING L EWIS ACID / BASE T HEORY Cr H 2 O  Cr(H 2 O) 6 3+ BeCl + H 2 O  BeCl(H 2 O) 2 AlCl 3 + CH 3 Cl  AlCl 3 CH 3 Cl SO 2 + H 2 O  SO 3 H 2 BF 3 + H 2 O  BF 3 H 2 O

T HE P H SCALE Measures how basic or acidic a solution is Measures the concentration of hydronium present pH = -log[H 3 O + ] pOH = -log[OH - ] pH + pOH = 14 pH > 7, basic solution pH < 7, acidic solution pH = 7, neutral solution

W HAT IS THE P H OF THE SOLUTIONS CONTAINING THE FOLLOWING CONCENTRATIONS OF HYDRONIUM IONS ? W HAT IS THE P OH OF THE SOLUTIONS ? 1x10 -2 M 3.5x10 -3 M 4x10 -7 M 2x10 -6 M 1x10 -9 M

W HAT IS THE HYDRONIUM ION CONCENTRATION FOR THE SOLUTIONS WITH THE FOLLOWING P H?

R EACTIONS OF A CIDS AND B ASES Neutralization The reaction between a strong acid and a strong base with produces salt and water Double replacement reaction Salt An ionic compound that does not have H + or OH - ions

C OMPLETE THE FOLLOWING NEUTRALIZATION REACTIONS Ca(OH) 2 + HNO 3  NH 3 + H 2 SO 4  Mg(OH) 2 + H 3 PO 4  NaOH + HC 2 H 3 O 4  Ba(OH) 2 + HI 

N EUTRALIZATION R EACTIONS – G AS F ORMING If a gas forms, such as CO 2 (from H 2 CO 3 ), SO 2 (from H 2 SO 3 ), or NH 3 (from NH 4 OH), it is called a gas forming reaction. NH 4 Br + KOH  HC 2 H 3 O 2 + NaHCO 3  HCl + LiHSO 3 

C ONJUGATE A CIDS AND B ASES Conjugate Acid-Base Pair Pair of molecules or ions related by the loss of gain of a H+

C ONJUGATE A CIDS AND B ASES

Properties of conjugate acid-base pairs If an acid is strong, its conjugate base is very weak. H 3 O + is the strongest acid that can exist in water. Acids stronger than H 3 O + will react completely with water to form H 3 O + and a conjugate base. Acids weaker than H 3 O + will react with water to a lesser extent to produce H 3 O + and a conjugate acid (reversible reaction). OH - is the strongest base that can exist in water. Bases stronger than OH - will react completely with water to produce OH - and a conjugate acid.

I DENTIFY THE CONJUGATE ACID - BASE PAIRS IN THE FOLLOWING REACTIONS NH 3 + H 2 O  NH OH - HCl + H 2 O  H 3 O + Cl - H 2 O + CH 3 CO 2 H  H 3 O + CH 3 CO 2 - H 2 O + H 2 SO 4  H 3 O + + HSO 4 -

I DENTIFY THE CONJUGATE ACID - BASE PAIRS IN THE FOLLOWING REACTIONS S 2- + H 2 O  OH - + HS - PO HNO 3  NO HPO 4 2- C 2 O HC 2 H 3 O 2  HC 2 O C 2 H 3 O 2 - HCO 2 H + OH -  CO 2 H - + H 2 O

W HAT ARE YOUR QUESTIONS ?

A CID B ASE P ROPERTIES OF W ATER Can act as either an acid or a base. Base H 2 O (l) + CH 3 CO 2 H (aq) H 3 O + (aq) + CH 3 CO 2 - (aq) Acid NH 3 (aq) + H 2 O (l) NH 4 + (aq) + OH - (aq) Water can undergo ionization to a small extent. H 2 O (l) H + (aq) + OH - (aq) During this ionization, water can act as both the acid and the base. H 2 O (l) + H 2 O (l) H 3 O + (aq) + OH - (aq)

I ONIZATION C ONSTANTS Acid Ionization Constant Equilibrium constant for the ionization of an acid H 2 O (l) + HA (aq) H 3 O + (aq) + A - (aq) Base Ionization Constant Equilibrium constant for the ionization of a base NH 3 (aq) + H 2 O (l) NH 4 + (aq) + OH - (aq) K a = [H 3 O + ][A - ] [HA] K b = [NH 4 + ][OH - ] [NH 3 ]

I ONIZATION C ONSTANTS For conjugate acid-base pairs, the ionization constants are related using the following equation CH 3 COOH (aq) H + (aq) + CH 3 COO - (aq) CH 3 COO - (aq) + H 2 O (l) CH 3 COOH (aq) + OH - (aq) H 2 O (l) H + (aq) + OH - (aq) K w = K a K b

Calculate the pH of a 0.5M solution of acetic acid in aqueous solution: HC 2 H 3 O 2(aq) C 2 H 3 O 2 - (aq) + H + (aq)

Calculate the pH of a 0.65M solution of HF in aqueous solution: HF (aq) F - (aq) + H + (aq)

What is the pH of a 0.25M solution of ammonia?

The pH of a 0.30M solution of acetic acid is Calculate the K a of the acid?

The pH of a 0.15M solution of hydrofluoric acid is Calculate the K a of the acid?

The pH of a 0.75M solution of methylamine, CH 3 NH 2, is Calculate the K b of the base?

P ERCENT I ONIZATION Percent Ionization The higher the percent ionization, the stronger the acid % Ionization = x 100 Ionized acid concentration at equilibrium Initial concentration of acid

The pH of a 0.30M solution of acetic acid is What is the percent ionization?

The pH of a 0.15M solution of hydrofluoric acid is What is the percent ionization?

D IPROTIC AND POLYPROTIC ACIDS Produce more than 1 hydrogen per mole when ionized. Ionization occurs in several steps. H 2 SO 3(aq) H + (aq) + HSO 3 - (aq) HSO 3 - (aq) H + (aq) + SO 3 2- (aq)

When sulfurous acid is dissolved in water, it dissociates in two steps. Calculate the concentrations of all species present at equilibrium in a 0.25M solution. H 2 SO 3(aq) H + (aq) + HSO 3 - (aq) HSO 3 - (aq) H + (aq) + SO 3 2- (aq)

W HAT ARE YOUR QUESTIONS ?

M OLECULAR S TRUCTURE AND THE S TRENGTH OF A CIDS Properties affecting the strength of acids Properties of the solvent Temperature Molecular structure of the binary acid Ionization The stronger the bond, the weaker the acid Going down a column on the periodic table, the size of the molecule increases, the bond strength decreases, and the strength of the acid increases. Higher the polarity of the molecule, the stronger the acid Going across a row of the periodic table, the electronegativity increases, the bond polarity increases, and the acid strength increases.

M OLECULAR S TRUCTURE AND THE S TRENGTH OF A CIDS Hydrohalic Acids Acids containing a halogen The bond strength in these acids has a larger influence over the strength of the acid than the polarity of the molecule HF < HCl < HBr < HI

M OLECULAR S TRUCTURE AND THE S TRENGTH OF A CIDS Oxoacids Contain H, O, and a third element Oxoacids with different central atoms from the same group on the periodic table with the same oxidation number As the electronegativity of the central atom increases, the acid strength increases Oxoacids with the same central atom but different numbers of attached groups As the oxidation number of the central atom increases, so does the acid strength HClO 4 > HClO 3 > HClO 2 > HClO

Which of the following acids has the greatest strength? NH 3 or PH 3 HI or H 2 Te HSO 3 - or H 2 SO 3 H 3 AsO 3 or H 3 AsO 4 HSO 4 - or HSeO 4 -

A CID -B ASE P ROPERTIES OF S ALTS Salts Strong electrolytes that dissolve completely in water NaCl, NaNO 3, KBr Salt Hydrolysis The reaction of an anion or a cation of a salt, or both, with water. Affects the pH of water

A CID -B ASE P ROPERTIES OF S ALTS Salts that produce neutral solutions CaCl 2(aq) Ca + (aq) + 2Cl - (aq) Salts that produce basic solutions CH 3 COONa (aq) Na + (aq) + CH 3 COO - (aq) CH 3 COO - (aq) + H 2 O (l) OH - (aq) + CH 3 COOH (aq) Salts that produce acidic solutions NH 4 Cl (aq) NH 4 + (aq) + Cl - (aq) NH 4 + (aq) + H 2 O (l) NH 3 (aq) + H + (aq)

A CID -B ASED P ROPERTIES OF S ALTS K b > K a, then the solution is basic because the anion will hydrolyze to a great extent than the cation K b < K a, then the solution will be acidic because cation hydrolysis will be greater than anion hydrolysis K b = K a, then the solution will be near neutral pH

Predict weather a salt solution is acids, basic, or neutral? NaCN LiF KNO 3 NaHCO 3 NaC 7 H 5 O 2

A CID -B ASE P ROPERTIES OF O XIDES Basic oxides will form bases when reacted with water. Na 2 O + H 2 O  NaOH Acidic oxides will form an acid when reacted with water. SO 3 + H 2 O  H 2 SO 4 Reactions between acidic/basic oxides and acids/bases produce salt and water. Na 2 O + 2HCl  2NaCl + H 2 O SO 3 + 2LiOH  Li 2 SO 4 + H 2 O Amphoteric oxides can act as both an acid and a base.

A CIDIC, B ASIC, AND A MPHOTERIC O XIDES

A CID -B ASE P ROPERTIES OF H YDROXIDES Alkali and alkaline metal hydroxides are basic – Except for Be(OH) 2 Many metal hydroxides are amphoteric Al(OH) 3, Sn(OH) 2, Pb(OH) 2, Cr(OH) 2, Cu(OH) 2, Zn(OH) 2, Cd(OH) 2 Sn(OH) 2 + 2H +  Sn 2+ + H 2 O Sn(OH) 2 + 2OH -  Sn(OH) 4 2- All amphoteric hydroxides are insoluble.

W HAT ARE YOUR QUESTIONS ?