Question

Indicate whether the pH increases, decreases, or remains the same when each of the following is added.

(CH3NH3)Cl to a solution of CH3NH2

pyridinium nitrate, (C5H5NH)(NO3) to a solution of pyridine, C5H5N

sodium formate to a solution of formic acid

how do you know these?

Answer 1

You recognize what the hydrolysis products are; alternately, recognize the kind of a salt you have. I use the latter and my instructions may take a few liberties with actual chemical processes; however, they always give the correct answer.
strong acid is SA; example HCl, HBr,etc.
weak acid is WA; example acetic acid
strong base is SB; KOH, NaOH, etc
weak base is WB; NH3, organic NH2 etc.

CH3NH3Cl is the salt of CH3NH2&HCl. That's a SA and WB. So it is acid.

sodium formate is the salt of formic acid and NaOH. NaOH SB, formic acid is WA. So it is basic

SA + SB = neutral
SA + WB = acid
WA + SB = basic
WA + WB = acid, basic, neutral and i all depends upon which which has the larger Ka or Kb. If Ka is larger it is acid; if Kb is larger it is basic. If Ka = Kb it is neutral.

Answer 2

so how do i know if the ph is changing?