According to the Bronsted-Lowry model there is an inverse relationship between t

Question

According to the Bronsted-Lowry model there is an inverse relationship between the strength of an acid (or base) and the strength of its conjugate base (or acid). Test this relationship using your experimental data for CH_3CO_2H, CH_3CO_2^1-, NH_3, and NH_4^1+. a) Write the equation for the reaction of CH_3CO_2H with water and identify the conjugate acid-base pairs. b) Write the equation for the reaction of NH_3 with water and identify the conjugate acid-base pairs. c) Which is the stronger acid, CH_3CO_2H or NH_4^1+? Which is the stronger base, CH_3CO_2^1- or NH_3? Explain your reasoning. Is this the behavior expected from the Bronsted-Lowry model? d) Using your values for K_a and K_b in table 2, calculate the value of K_a (conjugate acid) times K_b (conjugate base) for: i. acetic acid and the conjugate base acetate ii. ammonia and the conjugate acid ammonium iii. How well do your values agree with the Bronstcd-Lowry equation K_a (HA) rimes K_b (A^1-) = K_w?

Explanation / Answer

5. Bronsted-Lowry acid-base

a) For CH3COOH

CH3COOH + H2O <===> CH3COO-   + H3O+

     acid           base            conjugate   conjugate  

                                             base            acid

CH3COOH/CH3COO- are the acid/conjugate base pair

H2O/H3O+ are the base/conjugate acid pair

b) For NH3

NH3 + H2O <====> NH4+   +     OH-

base   acid           conjugate      conjugate

                               acid              base

NH3/NH4+ are the base/conjugate acid pair

H2O/OH- are the acid/conjugate base pair

c) CH3COOH with higher Ka value is a stronger acid than NH4+ (having lower Ks value)

Similarly, NH3 with higher Kb value is a stronger base than CH3COO- (having lower Kb value)

Yes, the behavior is as per the expectation of Bronsted-Lowry model.

d) Ka x Kb for,

i. acetic acid and conjugate base acetate

= 1.8 x 10^-5 x 5.55 x 10^-10 = 1.0 x 10^-14

ii. ammonia and the conjugate acid NH4+

= 1.8 x 10^-5 x 5.55 x 10^-10 = 1.0 x 10^-14

iii. According to the calculations shown in i. and ii., the Bronsted-Lowry assumption Ka(HA) x Kb(A-) = Kw match exactly.

Related Questions

Navigate

• Browse (All)
• Browse A
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.