Unit 2) 5) Equilibrium : Ka and pH Of Weak Acids

Question 1

Recap: you already know

• Strong acids and bases are ______ dissociated in aqueous solution
• weak acids and weak bases are _____ dissociated in aqueous solution
• hydrogen ions only exist as _____ ions in aqueous solution so we usually write their formula as H3O+ and these are known as hydronium ions
• in acidic solutions there are _____ hydronium ions than hydroxide ions
• in alkaline solutions there are ____ hydronium ions than hydroxide ions

Answer 1

• Fully
• partially
• hydrated
• more
• less

Question 2

A hydrogen ion is a hydrogen atom that has lost an electron and so is really just a ____

Answer 2

Proton

Question 3

What are acids and bases according to bronsted lowery

Answer 3

Acid is proton donor

Base is proton acceptor

Question 4

• when an acid donates a proton, the species left is known as the ________ ____
• when a base accepts a proton , the species that is left is known as the _______ ____

Answer 4

• conjugate base
  (For every acid a conjugate base is formed when the acid loses a proton )
• conjugate acid
  ( for every base a conjugate acid is formed when the base gains a proton )

Question 5

Table of acid , base and conjugate acids and bases

Answer 5

Notes

Or brightRED page 36

Question 6

How dissociated and how strong / weak is the conjugate acid /base of a

• strong acid
• weak acid
• strong alkali
• weak alkali

Answer 6

Strong acid

• fully dissociated in solution
• has weak conjugate base

Weak acid

• partially dissociated in solution
• has strong conjugate base

Strong alkali

• fully dissociated in solution
• has weak conjugate acid

Weak alkali

• only partially dissociated in solution
• has a strong conjugate acid

Question 7

For strong monoprotic acids such as HCL or HNO3 how does the hydronium ion concentration compare to the concentration of the acid

Answer 7

The hydronium ion concentration is the same as th concentration of the acid, this is because strong acids fully dissociate or ionise in water (all original acid molecules have changed into ions) so in 0.10 mol of HCL there is 0.10 mol of hydronium ions

Question 8

How does the hydronium ion concentration compare to the concentration Of the acid in weak acids

Answer 8

• in weak acids the hydronium ion concentration is much lower than the concentration of the acid
• this is beacause weak acids are partially dissociated in aqueous solution , less than 1% of molecules become ions in water.
  We therefore need a method to calculate the H3O+ concentration and pH of a weak acid

Question 9

What is the dissociation constant of a weak acid

Answer 9

Ka
Can be expressed as
Ka = [H+] [A] / [HA]

Where H is the conjugate acid , A is the conjugate base and HA is the acid

Question 10

Expression that you to calculate pH of a weak acid

Answer 10

pH = 1/2 pKa - 1/2log10c

This is in the data booklet

Question 11

Where can value of Ka and pKa be found

Answer 11

In the data booklet

Question 12

Calculations + how the expression comes along

Answer 12

Bright red page 37

Question 13

• The higher the Ka the ______ the acid
• the higher the Ka the _______ the tendency for molecules to form ions
  The higher the Ka the _____ the pKa

Answer 13

• Stronger
• greater
• lower