Midterm Exam 2 Chem 3A Dr. Perso April 5, 2018 Problem 4 (8 pts): Identify the a

Question

Midterm Exam 2 Chem 3A Dr. Perso April 5, 2018 Problem 4 (8 pts): Identify the acid, base, conjugate acid, and conjugate base in the following chemical reaction. NH3 (aq) + H2O (l)-) NH4+ (aq) + OH' (aq) Problem 5 (8 pts): Calculate the hydronium ion concentration and pH of a 0.050 M sodium hydroxide solution (0.050 M hydroxide ion). Recall that, as a strong base, sodium hydroxide dissociates completely in solution. Kw can be found under select weak acids and bases on your blue periodic table handout

Explanation / Answer

Problem-4

     NH3(aq) + H2O(l) ------------------- NH4+(aq)    + OH-(aq)

base             acid                      conjugate acdi conjugate base

conjugate acid base pair is         NH3(aq) --------- NH4+(aq) ( difference by one proton)

conjugate acid base pair is        H2O(l) ---------------- OH-(aq)

An acid -base pair which differes one proton (H+) IS Called conjugate acid-base pair

According to Bronsted-lowry theory ,

An acid means the substance which can donates the one proton(H+)

A base means the substane which can accept the one proton.

problem-5)

concentration of NaOH = 0.050M

NaOH --------------- Na+ + OH-

[OH-] =0.05M

[H3O+][OH-] = Kw                     where Kw= ionic product of water= 1.0x10^-14

[H3O+] = Kw/[OH-]

[H3O+] = 1.0x10^-14/0.05 = 20x10^-14

[H3O+] = 2.0x10^-13M

[H3O+] = [H+] = 2.0x10^-13M

-log[H+] = -log(2.0x10^-13)

PH= 12.698

PH= 12.7

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