Aqueous Solutions and pH

Ch15 sec 1

Hydronium & Hydroxide ions Self-ionization of water: 2 water molecules

produce a hydronium ion and a hydroxide ion by transfer of a proton.

Concentration of H3O+ and OH- in pure water are each only 1.0x10-7 mol/L at 25oC.

[H3O+] = hydronium ion concentration in moles per liter

Hydronium & Hydroxide ions Ex)

[H3O+] = 1.0x10-7 M & [OH-] = 1.0x10-7 M

The produce of [H3O+] & [OH-] remains constant in water at constant temp.

Ionization constant of water (Kw) Kw = [H3O+] [OH-] Kw = (1.0x10-7M) (1.0x10-7M)= 1.0x10-14M2

Kw increases as temperature increases

Neutral, Acidic, & Basic Solutions Since the hydronium and hydroxide ion

concentrations are the same, pure water is neutral. So any solution where [H3O+]=[OH-] is neutral

If [H3O+] > 1.0x10-7M the solution is acid If [OH-] > 1.0x10-7M the solution is basic

Calculating [H3O+] & [OH-] Recall; strong acids and bases completely

ionize in aqueous solutions.NaOH Na+ + OH-

1mol 1mol 1mol1.0x10-2M NaOH will produce [OH-] = 1.0x10-2M1.0x10-2 > 1.0x10-7 the solution is basic

practice A 1.0x10-4 M solution of HNO3 has been

prepared for a laboratory experiment. Calculate the [H3O+] & [OH-]

[H3O+] = 1.0x10-4 M [OH-] = 1. 0x10-10 M

practice Determine the hydronium and hydroxide

ion concentrations in a solution that is 1.0x10-4 M HCl

Ans [H3O+] = 1x10-4 M [OH-] = 1x10-10 M

practice Determine the hydronium and hydroxide

ion concentrations in a solution that is 1.0x10-3M HNO3

Ans [H3O+] = 1x10-3 M [OH-] = 1x10-11 M

practice Determine the hydronium and hydroxide

ion concentrations in a solution that is 3.0x10-2M NaOH

[H3O+] = 3.3x10-13 M [OH-] = 3.0x10-2 M

practice Determine the hydronium and hydroxide

ion concentrations in a solution that is 1.0x10-4M Ca(OH)2.

[H3O+] = 5.0x10-11 M [OH-] = 2.0x10-4 M