CHALLENGE 1

KEY QUESTIONS How do we define an acid? How do we define a base?

CHALLENGE 2 1.What was the first ever definition of an acid, and who proposed it? 2. Who then proposed the next definition? 3. Who proposed the new, improved definition? 4. Which scientist, then did a comprehensive study of acids and bases?

HISTORY 1777 – Lavoisier Acids are compounds that contain oxygen. But then, HCl was discovered 1810 Davy Acids are compounds that contain hydrogen Liebig An acid is a compound containing hydrogen, that can react with a metal to produce hydrogen gas 1884 Arrhenius When acids, bases and salts dissolve in water, they separate into ions in solution. He called them electrolytes. Acids are electrolytes that produce H+ ions.

ARRHENIUS’ THEORY HA (aq) H+ (aq) + A- (aq) B (aq) + H 2 O(l) BH (aq) + OH- (aq)

APPLYING ARRHENIUS’ THEORY HA (aq) H+ (aq) + A- (aq) B (aq) + H 2 O(aq) BH (aq) + OH- (aq) HCl (aq) + NaOH(aq) NaCl(aq) + H 2 O (aq) Use the theory to explain what is happening during neutralisation.

APPLYING ARRHENIUS’ THEORY HCl (aq) + NaOH(aq) NaCl(aq) + H 2 O (aq) H+ (aq) + OH-(aq) H 2 O (aq) Apply the theory to explain neutralisation. Arrow shows the reaction goes to completion

WHICH IS TRUE? Oxonium ion HA (aq) H+ (aq) + A- (aq) HA (aq) + H 2 O(l) H 3 O+ (aq) + A- (aq) Acids do not dissolve in other solvents such as organic solvents, other than water; they are non-electrolytes in other solvents as they contain no H+ ions. Does this evidence support the equilibrium? If the rate at which electrical current moves in an acidic solution is measured, how can this be used to confirm the existence of the H 3 O + ion?

WHAT ABOUT THIS REACTION? NH 3 (g) + HCl (g) NH 4 Cl (s) Does Arrhenius’ theory still hold true? NH 3 + H 2 O NH OH - HCl + H 2 O Cl - + H 3 O + What’s reacting in this neutralisation reaction? Why does water not appear in the overall

CHALLENGE 3 What definition of an acid and a base did two scientists: Bronsted and Lowry, propose? Are their definitions better? Explain why.

“A SUBSTANCE WHICH DONATES PROTONS IN A REACTION. A PROTON DONOR.” Bronsted-Lowry Acid

“A SUBSTANCE WHICH ACCEPTS PROTONS IN A REACTION. A PROTON ACCEPTOR.” Bronsted-Lowry Base

“INVOLVE PROTON TRANSFER FROM ACID TO BASE.” Bronsted-Lowry Acid-Base reactions

WHAT ABOUT THIS REACTION? NH 3 (g) + HCl (g) NH 4 Cl (s) Can we use Bronsted-Lowry definitions to explain? NH 3 + H 2 O NH OH - HCl + H 2 O Cl - + H 3 O + What is acting as an acid? What is acting as a base?

EXAMPLE: The reaction between sodium carbonate and hydrochloric acid. Na 2 CO 3 + 2HCl 2NaCl + CO 2 + H 2 O In ionic form, this is written as:

EXAMPLE 1 The reaction between sodium carbonate and hydrochloric acid. Na 2 CO 3 + 2HCl 2NaCl + CO 2 + H 2 O In ionic form, this is written as: CO 3 2- (aq) + 2H + (aq) CO 2 (g) + H 2 O(l)

H 2 SO 4 (aq) + HNO 3 (aq) ↔ H 2 NO 3 + (aq) + HSO 4 - (aq) H 2 SO 4 = Bronsted-Lowry acid (H + donor) HNO 3 = Bronsted-Lowry base (H + acceptor) HSO 4 - = Bronsted-Lowry base H 2 NO 3 + = Bronsted-Lowry acid Base 1 Acid 1Base 2 Acid 2 Identify the acid and base in the forward & backward reactions

H 2 SO 4 (aq) + HNO 3 (aq) ↔ H 2 NO 3 + (aq) + HSO 4 - (aq) Conjugate acid-base pairs? Base 1 Acid 1Base 2 Acid 2 Identify the acid and base in the forward & backward reactions

CONJUGATE PAIRS base acid HA + H 2 O A - + H 3 O + acid base Conjugate pair

H 2 O(aq) + NH 3 (aq) ↔ NH 4 + (aq) + OH - (aq) H 2 O = Bronsted-Lowry acid (H + donor) NH 3 = Bronsted-Lowry base (H + acceptor) OH - = Bronsted-Lowry base NH 4 + = Bronsted-Lowry acid Acid 1Base 2 Acid 2 Base 1

CH 3 COOH(l) + HClO 4 (l) ↔ CH 3 COOH 2 + (l) + ClO 4 - (l) HClO 4 = Bronsted-Lowry acid (H + donor) CH 3 COOH = Bronsted-Lowry base (H + acceptor) ClO 4 - = Bronsted-Lowry base CH 3 COOH 2 + = Bronsted-Lowry acid Acid 1 Base 2 Acid 2 Base 1

H 2 O(aq) + HCl(aq) ↔ Cl- (aq) + H 3 O + (aq) HCl = Bronsted-Lowry acid (H + donor) H 2 O = Bronsted-Lowry base (H + acceptor) Cl - = Bronsted-Lowry base H 3 O + = Bronsted-Lowry acid Acid 1 Base 2Acid 2 Base 1

H 2 O(l ) + HSO 4 - (aq) ↔ SO 4 2- (aq) + H 3 O + (aq) HSO 4 - = Bronsted-Lowry acid (H + donor) H 2 O = Bronsted-Lowry base (H + acceptor) SO 4 2- = Bronsted-Lowry base H 3 O + = Bronsted-Lowry acid Acid 1 Base 2Acid 2 Base 1

H 2 O(aq) + H 2 O(aq) ↔ H 3 O + (aq) + OH - (aq) H 2 O = Bronsted-Lowry acid (H + donor) H 2 O = Bronsted-Lowry base (H + acceptor) OH - = Bronsted-Lowry base H 3 O + = Bronsted-Lowry acid Base 1 Acid 1Base 2 Acid 2

Strong vs weak? Monoprotic vs diprotic Monobasic vs dibasic?