6.1 a/c/f: Intro to acid and base & Ka and Kb

Intro to acids/bases & Ka and Kb

Y12 Chem

​Syllabus dot points

6.1 a investigate the correct IUPAC nomenclature and properties of common inorganic acids and bases

c predict the products of acid reactions and write balanced equations to represent:

– acids and bases

– acids and carbonates

– acids and metals

f explore the changes in definitions and models of an acid and a base over time to explain the limitations of each model, including but not limited to:

– Arrhenius’ theory

– Brønsted–Lowry theory

​What we will cover today...

• ​what is an acid and what is a base?

• how to name acids (and bases)

• conjugate acid/base pairs ​

• ​Ka and Kb defintions

​What is an acid and a base?

• ​several definitions

• ​developed over time - used to be based on simpler observations (litmus tests, reactions)

• ​there are several theories/definitions:

  • ​Arrhenius

  • ​Bronsted-Lowry

  • ​Lewis

Open Ended

Do you remember any of these definitions of an acid or a base?

​Arrhenius

• ​Acids = any substance that dissociates (breaks apart) and ​produces H+ ions

• ​Bases = dissociate in water to produce hydroxide ions

​Bronsted-Lowry

• ​Acids = proton donors

• ​Bases = proton acceptors

• ​an acid base reaction will involve an exchange of protons from an acid to a base

  • ​usually in the form of an H+ ion

• ​this expands acid/base reactions out a solution

​Lewis

• ​Acid = substance that accepts a pair of electrons

• ​Base = substance that donates a pair of electrons

Multiple Choice

According to Bronsted-Lowry acid base theory, an acid is a.....

• Proton donor
• Proton acceptor
• Produces H+ when added to water
• Made of H+

Multiple Choice

According to which theory is a base a substance which produces OH- ions in water?

• Arrhenius
• Bronsted-Lowry
• Lewis

Multiple Choice

According to Lewis acid-base theory, a Lewis base is.....

• an electron pair acceptor
• an electron pair donor
• an oxidising agent
• a reducing agent

Multiple Choice

Which reactant in the following equation is a Bronsted acid?

• ammonium
• ammonia
• hydroxide
• water

​Properties of acids and bases

​Naming Acids

​Reactions of acids

• ​acid + base -> salt + water

• acid + carbonate -> salt + carbon dioxide + water

• acid + metal -> salt + hydrogen gas

Multiple Choice

Which of the following chemical reactions represents an acid-base reaction?

• HBr + KOH → KBr + H₂O

• ZnCl₂ + MgSO₄ → ZnSO₄ + MgCl₂

• H₂SO₄ + CaCl₂ → CaSO₄ + HCl

• NH₄OH + KCl → KOH + NH₄Cl

Multiple Choice

Identify the salt in the following equation:

HNO₃ + Zn(OH)₂ → Zn(NO₃)₂ + H₂O

• HNO₃

• Zn(OH)₂

• Zn(NO₃)₂

• H₂O

Multiple Choice

An acid reacts with metal to produce 

• Carbon dioxide 
• Hydrogen gas
• Hydrogen gas and water 
• Salt and hydrogen gas 

Multiple Choice

Complete the following reaction:
Hydrochloric acid + magnesium hydroxide --> 

• Magnesium chloride + water 
• Magnesium + water
• Magnesium chloride + hydrogen gas 
• Magnesium chloride + water + carbon dioxide 

​Conjugate acid-base pair

• ​two molecules or ions that differ by one proton (H+ ion)

• ​we consider this relationship in terms of the reactions that occur

• ​e.g. HCl and Cl^- are a conjugate acid-base pair. Cl^- is formed from HCl by the loss of a single proton, and is the conjugate base of HCl.

Multiple Choice

What is the conjugate acid in the following equation?

• PO₄^3- 
• HNO₃ 
• NO₃^- 
• HPO₄^2-
  

Multiple Choice

What is the conjugate base in the following reaction?

• HCO₃^- 
• HCl
•  H₂CO₃ 
• ^Cl-

​Strong vs Weak Bases

• ​strong ionises completely in a solution

• ​weak only partially ionises

• ​therefore, the ionisation of a weak acid or bases is a reversible reaction - as it never fully goes to completion

• ​weak acids = HA

• ​conjugate base = A^-

• ​weak base = B

• ​conjugate acid = BH⁺

​Ka and Kb

• ​acid dissociation constant

• ​base dissociation constant

• ​describes the degree of ionisation of an acid or a base - and therefore indicate the strength of the acid or base

​Ka

• ​general equation for the ionisation of a weak acid in water

  • ​HA is the acid (donates a proton)

  • ​A^- is the conjugate base

  • ​H3O could be written as H+, however, free H+ doesn't exist in solution

• ​the larger the Ka, the stronger the acid and the higher the H+ concentration at equilibrium

​Kb

• ​weak bases react with water and produce hydroxide ions

• ​In general reaction:

  • ​B = the parent base

  • ​BH = conjugate acid

• ​the larger the Kb, the stronger the base and the higher the OH^- concentration at equilibrium

​Next Few Lessons

• ​Acid/base general reactions

• ​Indicators

• Enthalpy of Neutralisation