5.3 e: Keq and Different Reactions

Keq and Different Reactions

Chem 12

​Syllabus dot points

• ​5.3 e

• explore the use of Keq for different types of chemical reactions, including but not limited to: – dissociation of ionic solutions – dissociation of acids and bases

​What we will be covering...

• ​what is solubility equilibria

• ​dissociation of acids and bases

• ​practice questions

​Solubility Equilibria

• ​a state of dynamic equilibrium that exists when a solid species dissociates into an ionic solution of that species

• dissociation = where a species splits into a smaller molecule (usually an ion)

• ​have to determine net ionic equations (Year 11)

  • ​then 'convert' to an equilibrium equation, where the solid is on the reactant side

​K_sp

• ​the equilibrium expression for dissolved ionic solid solutions is called the solubility product

• ​don't include the solids as part of a heterogenous system

• ​value wise --> the smaller the Ksp for a precipitate, the less solubility it has

• ​only used when the system is at equilibrium, if it isn't, we are just measuring Q, or the ionic product

​Dissociation of acids and bases

• ​go into more detail in Module 6

• ​strong and weak

  • ​strong = complete ionisation in water

  • ​weak = partial ionisation in water

​Dissociation of acids: Ka

• When a weak acid only partially dissociates in water you get an equilibrium system, with: the acid, hydrogen ions, and the anion of the acid

• The larger the Ka - the larger the degree of dissociation - more products

​Dissociation of bases: Kb

• Same as for acids. Weak bases produce an equilibrium system where the base, hydroxide ions, and the cation of the base is present

Multiple Choice

What is the role of water in the dissociation of acids?

• It acts as a solvent and facilitates the dissociation

• It neutralizes the acid

• It reacts with the acid to form a base

• It has no role

Multiple Choice

In a titration experiment, what does a high K_a value indicate about the acid being titrated?

• The acid is strong and dissociates completely

• The acid is weak and dissociates partially

• The acid is neutral

• The acid is a base

Multiple Choice

What is the significance of a low K_a value in an acid?

• The acid is weak and dissociates partially

• The acid is strong and dissociates completely

• The acid is neutral

• The acid is a base

Multiple Choice

How does the presence of a common ion affect the acid dissociation constant (K_a)?

• It decreases the dissociation of the acid

• It increases the dissociation of the acid

• It has no effect

• It neutralizes the acid

​Next up:

Solution equilibria