Bronsted Lowry Acids and Bases Arrhenius Acid An
Bronsted Lowry Acids and Bases • Arrhenius Acid: An Arrhenius acid produces hydronium ions [H 3 O+] when it dissociates in water. • Bronsted-Lowry Acid: Proton donor; donates hydrogen ions [H+] to the base. • Arrhenius Base: An Arrhenius Base produces hydroxide ions [OH-] when it dissociates in water. • Bronsted-Lowry Base: Proton acceptor; accepts hydrogen ions [H+] from the acid. • Bronsted-Lowry is an improved definition • Arrhenius works better for SA/SB. • Bronsted-Lowry works better for WA/WB.
Conjugate Acid-Base Pairs • A conjugate pair refers to acids and bases with common features. These common features are the equal loss/gain of protons between the pairs. Conjugate acids and conjugate bases are characterized as the acids and bases that lose or gain protons. In an acid-base reaction, an acid plus a base reacts to form a conjugate base plus a conjugate acid.
Conjugate Acid-Base Pairs Acid + Base → Conjugate Base + Conjugate Acid • The conjugate acid of a base is formed when the base gains a proton. NH 3(g) + H 2 O(l)→NH 4+ (aq) + OH−(aq) NH 4+ is the conjugate acid to the base NH 3, because NH 3 gained a hydrogen ion to form NH 4+.
Conjugate Acid-Base Pairs Acid + Base → Conjugate Base + Conjugate Acid • The conjugate base of an acid is formed when the acid donates a proton. NH 3(g) + H 2 O(l)→NH 4+ (aq) + OH−(aq) OH- is the conjugate base to the acid H 2 O, because H 2 O donates a hydrogen ion to form OH-. Note: The stronger the acid or base, the weaker the conjugate. The weaker the acid or base, the stronger the conjugate.
How To Identify Conjugate Pairs HNO 3 + H 2 O → H 3 O+ + NO 3 - 1. HNO 3 is an acid because it donates a proton to water and its conjugate base is NO 3 -. An easy way to identify the conjugate base is that it differs from the acid by one proton. 2. H 2 O is a base because it accepts a proton from HNO 3 and its conjugate acid is H 3 O+. Again to identify the conjugate acid (or any conjugate pair) is that it differs from the base by one proton.
How To Identify Conjugate Pairs Practice Problems Identify the acid, base, conjugate acid and conjugate base for the following reactions: 1. 2. 3. 4. 5. HF + H 2 O→ F− + H 3 O+ HSO 4 - + NH 3 → SO 42 - + NH 4+ C 2 H 3 O 2 - + HCl → HC 2 H 3 O 2 + Cl− HNO 2 + H 2 O → H 3 O+ + NO 2 HCN + H 2 O → H 3 O+ + CN−
Amphoteric Substances • A substance which can act as either an acid or a base is described as being amphoteric.
Ionization Constant of Weak Acid CH 3 COOH + H 2 O ↔ H 3 O+ + CH 3 COOKa = [H 3 O+][CH 3 COO-] [CH 3 COOH] Ka is the acid ionization constant. It is constant for a given temperature, but has a new value for each new temperature.
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