Problem 4.40


Write the balanced molecular and net ionic equations for each of the following neutralization reactions.

(a)Aqueous acetic acid is neutralized by aqueous barium hydroxide.

Notice in an acid-base reaction that the acid transfers its proton (H+) to the base. In this case, acetic acid, CH3COOH, transfers its proton to OH-. A nice way to think about this is to write the reactants and switch the anions and cations to get the products:

write the reactants: CH3COOH(aq) + Ba(OH)2(aq) ------>

split these up into their component ions: H+ + CH3COO- + Ba2+ + OH- ------>

switch anions and cations and predict products: CH3COOH(aq) + Ba(OH)2(aq) ---> Ba(CH3COO)2(aq) + H2O(l)

Now we balance...

2CH3COOH(aq) + Ba(OH)2(aq) ---> Ba(CH3COO)2(aq) + 2H2O(l)

The salt here is Ba(CH3COO)2 (barium acetate). Note that the products of a neutralization reaction between an acid and a metal hydroxide produces water and a salt.

In net ionic form, we have

CH3COOH(aq) + OH-(aq) ---> CH3COO-(aq) + H2O(l)

note that we do not ionize the weak electrolyte (acetic acid) on the reactant side!

(b) Solid chromium (III) hydroxide reacts with nitrous acid.

Again, we have an acid reacting with a base, so we will get water and a salt as products.

write out the reactants: HNO2(aq) + Cr(OH)3(s) ----->

switch partners to predict products, and balance: 3HNO2(aq) + Cr(OH)3(s) ----> Cr(NO2)3(aq) + 3H2O(l)

The salt here is chromium (III) nitrite. In net ionic form,

3HNO2(aq) + Cr(OH)3(s) ----> Cr3+(aq) + 3NO2- + 3H2O(l)

as if you haven't heard it enough, here's the nag: don't ionize the solid reactant! Also - nitrous acid is a weak electrolyte. Do not ionize it!!

(c) aqueous nitric acid and aqueous ammonia react.

OK. You should recognize nitric acid as a strong acid, and ammonia (NH3) as a weak base (it's the only weak base we'll consider right now.) You should also kow the definitions of acids and bases - acids donte protons and bases accept them. So, using this definition, nitric acid will donate a proton and ammonia will accept a proton...

HNO3(aq) + NH3(aq) ==> NH4+(aq) + NO3-(aq)

See how the proton moves from the acid to the base? OK, now: we ionize nitric acid and cancel spectator ions, and we're left with

H+(aq) + NH3(aq) ==> NH4+(aq)


If you have any questions or comments, reply to chapman@sou.edu
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Doug Chapman chapman@sou.edu 7/18/14