Defining an acid

Question 1

What is the Bronsted-Lowry description of an acid and a base?

Answer 1

• a substance that can done a proton (H+) and base is a substance that can accept a proton

Question 2

what is acid-base equilibria?

Answer 2

• involve the transfer of protons

Question 3

What happens when a proton is in an aqueous solution?

Answer 3

• never found isolated
• always bonded to at least one water molecule to form the H₃O⁺ ion (oxonium)
  
  • for simplicity, protons in an aqueous solution are represented as H⁺ (aq) rather than H₃O⁺ (aq)

Question 4

Is water ionised?

Answer 4

• slightly ionised
  
  • H₂O (l) ⇌ H⁺ (aq) + OH^- (aq)
  • may be written as
    
    • H₂O (l) + H₂O (l) ⇌ H₃O⁺ + OH^-

Question 5

What is the ionic product of water?

Answer 5

• K_w = [H+] [OH-] = Kc x [H2O]
  
  • calculated from Kc

Question 6

How does the ionic product of water vary with temperature?

Answer 6

• formation of hydroxonium ions is endothermic
• Le Chaterliars, if you make a change to conditions of a reaction in dynamic eqm, the postion of eqm moves to counter the change you made
• increase in temp, eqm move to lower temp, move to endothermic side, forward reaction is favoured

Question 7

Why is [H2O] assumed to be fixed?

Answer 7

• change is so small
• therefore is a constant

Question 8

Why does water have a pH of 7 at 298K?

Answer 8

• hydorxide ion is strong base, oxonium ion is strong acid

Question 9

Why is water always neutral despite pH changing?

Answer 9

• equal conc of H+ and OH-
• if Kw changes, the neutral pH changes

Question 10

What is the value of Kw at room temp?

Answer 10

• 1x10^-14