U NIT 12 Acids and Bases

A CID AND B ASE D EFINITIONS Arrhenius Definition Acids produce H + or H 3 O + (hydronium) in water Bases produce OH - in water Bronsted-Lowry Definition Acids are proton donors (H + donors) Bases are proton acceptors (H + acceptors)

C ONJUGATE A CID -B ASE P AIRS HCl + H 2 O  H 3 O + + Cl - Conjugate acid – Got the H + Conjugate base – what’s left from the acid after it lost the H + H 2 O + H 2 SO 4  HSO H 3 O + NH 3 + HCl  NH Cl -

6 S TRONG A CIDS Strong Acids dissociate almost completely HCl – hydrochloric acid H 2 SO 4 – sulfuric acid HNO 3 – nitric acid HBr – hydrobromic acid HI – Hydroiodic acid HClO 4 – perchloric acid

C OMMON W EAK A CIDS Weak acids do not dissociate completely HC 2 H 3 O 2 or CH 3 COOH – acetic acid (vinegar) HF – hydrofluoric acid

D ISSOCIATION OF S TRONG /W EAK A CIDS

T HREE T YPES OF A CID Monoprotic – one proton Ex. HCl Diprotic – two protons Ex. H 2 SO 4 Triprotic – three protons Ex. H 3 PO 4

S TRONG B ASE Group I Metal + OH Ex. NaOH Group II Metal + OH Ex. Mg(OH) 2 Strong Bases dissociate completely

S ELF -I ONIZATION OF W ATER

P H S CALE

P H C ALCULATIONS

P H C ALCULATIONS M AP pHpOH

E XAMPLES

P H OF SOLUTIONS ( STRONG ACIDS AND BASES ) What is the pH of M NaOH? What is the pH of M Ca(OH) 2 ? What is the pH of M H 2 SO 4 ? Since strong acids and bases dissociate completely the concentration of H + or OH - depends on the number of them in the chemical.

T ITRATION A technique used to determine the unknown concentration of an acid or base using a neutralization reaction and an indicator Neutralization reaction Acid + Base  salt (ionic compound) + H 2 O Indicator – changes color based on pH of the solution, many different indicators, all have specific color changes at specific pH ranges

T ITRATION

Balancing out the number of hydrogen ions and hydroxide ions to make a neutral solution Add HCl to NaOH to perfectly balance H + and OH - Use an indicator that changes color when the pH is 7 (neutral)

E XAMPLE A 25mL sample of HCl was titrated with 15mL of 2M NaOH. What was the concentration of the acid?

E XAMPLE A 9.4 mL sample of 3.0M Ca(OH) 2 is titrated with 10. mL of HBr. What was the concentration of the acid?

T ITRATION Buret (or burette) is used to dispense the acid or base of known concentration

T ITRATION Equivalence Point – where acid and base have reached a neutral pH End point – where your indicator changes color

A CID /B ASE R EACTIONS THAT YOU SHOULD KNOW … 1. Metal + Acid  salt + H 2 Single replacement reaction __Al + __HCl  2. Metallic carbonate + Acid  salt + CO 2 + H 2 O Double replacement reaction __K 2 CO 3 + __HBr  3. Neutralization: Acid + Base  salt + water Double replacement reaction __H 2 SO 4 + __NaOH 

A CID /B ASE R EACTIONS 4. Metallic Oxide + H 2 O  forms a base Synthesis reaction MgO + H 2 O  Forms a metallic hydroxide Metallic oxides (like MgO) are called basic anhydrides (“base without water”)

A CID /B ASE R EACTIONS 5. Nonmetallic oxide + H 2 O  forms an acid Synthesis reaction SO 2 + H 2 O  Nonmetallic oxides are called acid anhydrides (“acid without water”)

A CID /B ASE R EACTIONS 6. Ionization of an Acid (in H 2 O) Acid + H 2 O  H 3 O + + another ion HCl + H 2 O  HC 2 H 3 O 2 + H 2 O  Self Ionization of water… H 2 O + H 2 O 

B UFFERED S OLUTIONS A solution of a weak acid and its salt Ex. HF and NaF pH is very stable, remains nearly constant if small amounts of acid or base are added

HCl, strong acid, dissociates H YDROLYSIS OF S ALTS What happens if I add a salt (ionic compound) to water? Can form an acid, a base, or a neutral solutions Example NaCl is added to water.. NaCl dissociates H 2 O self-ionizes into H + and OH - So in solution we have…. Na+ Cl- H+ OH- NaOH, strong base, dissociates Strong acid + strong base = neutral solution

H YDROLYSIS OF S ALTS Example Dissolve Na 3 PO 4 in water Example Dissolve AlBr 3 in water Weak acid+ strong base = basic solution Strong acid + weak base= acidic solution