Consider the ionization of the weak acid HF with water when 0.050 mol HF is diss
ID: 519677 • Letter: C
Question
Consider the ionization of the weak acid HF with water when 0.050 mol HF is dissolved in enough water to make a 0.500 L solution: HF(aq) + H_2O(l) H_2O^+ (aq) + F (aq) (a) Would you expect the moles of H_3O^+ in this solution to be the same, greater than, or less than the moles of H_3O^+ in the strong acid HNO_3 solution in #8? _____ Explain your answer. (b) Would you expect the hydronium ion molar concentration. [H_3O^+], in this solution to be the same, greater than, or less than the [H_3O^+] in the strong acid HNO_3 solution in #8? ____ Explain your answer. (c) Would you expect the pH of this solution to be the same, greater than, or less than the pH of the HNO_3 solution in #8?Explanation / Answer
9.) molarity = no. of mole / volume of solution in liter
Molarity of HF = 0.050 / 0.5 = 0.1 M
a) HF is weak acid thereofe it dissociate partioally
but HNO3 is strong acid therefore it dissociate completly
[H3O+] of 0.1 M HF is given below
Weak acid HF dissociates as HF +H2O F-+ H3O+
Ka = [F-][H3O+] / [HF]
but [F-] = [H3O+] = x
Ka = [x][x] / [HF]
Substitute the value in equation
Ka of HF = 6.6 X 10-4
6.6X10-4 = [x]2/ 0.1
[x]2 = 6.6X10-4 X 0.1 = 6.6X10-5
[x] = 0.00812
Concentration of H3O+ = 0.00812 M of HF of 0.1 M
but HNO3 is strong acid therefore it dissociate completly therefore [HNO3] = [H3O+] = 0.1 M
hence HF have less [H3O+] than HNO3 [H3O+ ] when both have same concentration
c) pH = -log[H3O+]
pH of 0.1 M HF = -log(0.00812) = 2.09
pH of 0.1 M HNO3 = -log(0.1) = 1
HF have high pH than HNO3 if both have same concentration.