“K” Chemistry (part 3 of 3) Chapter 15: Acids and Bases

Properties of Acids A sour taste Dissolves many metals Turns blue Litmus paper red Neutralizes bases Liberate the H + ion – Reacts to form hydronium –H3O+–H3O+ A STRONG ACID will dissociate 100% – What is HF not a strong acid??

Six Strong Acids

Properties of Bases A bitter taste Feel slippery to the touch Turn red Litmus paper blue The ability to neutralize acids Associated with the OH - anion What would be a strong base?? – Hint: Think about your solubility rules

Bases Bases feel slippery because they react with the oils on the skin to form a soap-like substance It is for this reason that bases are used as cleaning agents around the house

Definitions of Acids and Bases Three different working definitions of acids and bases: – Arrhenius – Brᴓnsted-Lowry – Lewis Why Have three?? Which is correct?? – Different definitions are convenient at different times and in different scenarios… no one perfect definition

The Arrhenius Definition Acid: A substance that produces H + ions in aqueous solution HCl (aq)  H + (aq) + Cl - (aq) – HCl is an acid because it produces H + ions Base: a substance that produces OH - ions in aqueous solution NaOH (aq)  Na + (aq) + OH - (aq) – NaOH dissociate completely and produced the hydroxide ion

Arrhenius Acids HCl (aq)  H + (aq) + Cl - (aq) Consider the acid… the H+ is aqueous – It continues and reacts with H2O to yield the hydronium ion H + (aq) + H 2 O (l)  H 3 O + (aq)

Acids and Bases HCl (aq)  H + (aq) + Cl - (aq) NaOH (aq)  Na + (aq) + OH - (aq) Under the Arrhenius Definition, acids and bases readily and naturally come together to form water: H + (aq) + OH - (aq)  H 2 O (l) Think way back… what does the reaction represent?

The Brᴓnsted-Lowry Definition Acid: A proton (H + ion) donor Base: A proton (H + ion) acceptor Again, HCl is an acid by this definition HCl (aq) + H 2 O (l)  H 3 O + (aq) + Cl - (aq) – The acid donates the proton to the water… HCl is an acid here… Water is _______________

Brᴓnsted-Lowry Base Think about ammonia… NH 3(aq) + H 2 O (l)  NH 4 + (aq) + OH - (aq) There is no OH - to be liberated from NH 3 (Arrhenius Definition), however, it does “accept a proton” from the water, making it a Brᴓnsted- Lowry Base!!

Amphoteric HCl (aq) + H 2 O (l)  H 3 O + (aq) + Cl - (aq) NH 3(aq) + H 2 O (l) NH 4 + (aq) + OH - (aq) Water plays a couple different roles here… – Water can be an acid OR a base depending on who is around… this trait is called Amphoteric

Conjugate Acid-Base Pairs NH 3(aq) + H 2 O (l) NH 4 + (aq) + OH - (aq) In the reverse rxn, the NH 4 + (acid) is the proton donor and the OH - is the proton accepter (base) NH 4 + and NH 3 are known as a conjugate acid- base pair – Two substances related to each other by the transfer of a proton

Conjugate Pairs NH 3(aq) + H 2 O (l) NH 4 + (aq) + OH - (aq) Base Conjugate Acid AcidConjugate Base

In an Acid-Base Reaction, – A base accepts a proton and becomes a conjugate acid – An acid donates a proton and becomes the conjugate base

Practice Identify the Bronsted-Lowry acid, the Bronsted-Lowry base, the conjugate acid, and the conjugate base (a)H 2 SO 4(aq) + H 2 O (l)  HSO 4 - (aq) + H 3 O + (aq) (b)HCO 3 - (aq) + H 2 O (l) H 2 CO 3(aq) + OH - (aq)

More Practice Identify the Bronsted-Lowry acid, the Bronsted-Lowry base, the conjugate acid, and the conjugate base (a)C 5 H 5 N (aq) + H 2 O (l) C 5 H 5 NH + (aq) + OH - (aq) (b)HNO 3(aq) + H 2 O (l)  H 3 O + (aq) + NO 3 - (aq)

Acids Monoprotic Acids – containing only one ionizable proton Diprotic Acids – an acid containing two ionizable protons – Polyprotic

Acid Ionization Constant (K a ) A Strong Acid dissociates COMPLETELY, whereas a weak acid only partially ionizes The amount the acid ionizes (regarding weak acids, not 100%) determines its strength – The “strength of weak acids” – not applicable to SA – they dissociate completely

Acid Ionization Constant (K a ) HA (aq) + H 2 O (l) H 3 O + (aq) + A - (aq) K eq = [prod]/[react] = K a If the equilibrium lies far to the right, the acid is strong (more dissociation) If the equilibrium lies far to the left, the acid is weak (only a small percentage of the acid molecules are ionized)

Strength of Acids The amount ionized is a clear indicator of the strength of an acid (SA completely…) The K a is a direct measure of where this equilibrium lies SA will have no reactants in the K a (completion reaction) – what does this mean about the magnitude of the K a ? WA will have a large quantity of reactants… what does this mean?

Left off on page 671 Refer to equations and notes on board… Additionally, read through the pH scale and the concentration calculations through the remaining sections of the chapter

Titrations Titrations – Buret – End Point – Equilibrium Point – Indicator Solution – Dilutions –