12.65 determine whether an aqueous solution of each of the following salts has a ph equal to, greater than, or less than 7. if ph 7 or ph 7, write a chemical equation to justify your answer. (a) nh4br; (b) na2co3; (c) kf; (d) kbr; (e) alcl3; (f) cu(no3)2.

a. pH > 7 ; b. pH > 7 ; c. pH = 7 ; d. pH = 7 ; e. pH < 7 ; f. pH < 7

Explanation:

a. NH₄Br → NH₄⁺  +  Br⁻

The ammonium is the conjugate strong acid from a weak base, so it will react in water. Bromine, is the conjugate weak base from a strong acid and it does not react in water. As the NH₄⁺ react as this:

NH₄⁺  + H₂O  ⇄  NH₃  +  OH⁻   (pH > 7;  brings hydroxyls to the medium)

b. Na₂CO₃  →  2Na⁺  +  CO₃⁻²

The sodium cation is the conjugate weak acid from a strong base, in water in does not react. The carbonate is the conjugate strong base from a weak acid, so it can react in water as this:

CO₃⁻²  + H₂O  ⇄  HCO₃⁻  + OH⁻

HCO₃⁻  + H₂O ⇄ H₂CO₃  + OH⁻ (pH > 7;  brings hydroxyls to the medium)

c. KF → K⁺  + F⁻

Both ions come from a base and a strong acid, so they will be the weak conjugate base and acid. They will not have a reaction in the water, so the solution will be neutral

d. KBr → K⁺  +  Br⁻    (same as before)

e. AlCl₃  →  Al³⁺  +  3Cl⁻

Cl⁻ is a conjugate weak base, from a strong acid and it doesn't react in water. But the Al³⁺ which comes from the Al(OH)₃ is amphoteric, it can act as an acid or a base. In this case, you have a complex and the solution will be acid.

Al³⁺  +  H₂O ⇄ Al(OH)²⁺  + H⁺ (it brings protons to the medium, pH < 7)

f. Cu(NO₃)₂  →  Cu²⁺  +  2NO₃⁻

Ion Cu²⁺ comes from the Cu(OH)₂, a weak base so it is a conjugate strong acid. The nitrate, comes from a strong acid (nitric) , so it is the conjugate weak base of it, it won't react in water.

Cu²⁻ + H₂O  ⇄  Cu(OH)⁺  +  H⁺

You will have a complex, and you are bringing protons to the medium, so pH < 7

c. 4.54 x 10–12 j happens to be correct