Rank the following 0.10 M solutions in order of increasing pH. (Use the appropriate symbol to separate substances in the list.)

Question

Rank the following 0.10 M solutions in order of increasing pH. (Use the appropriate <, =, or > symbol to separate substances in the list.)
 
      HONH3NO3,  HOBr, RbNO3, RbOH,  HNO3, HONH2,  RbOBr
                                                                 
HONH3NO3 (?)
HOBr     (weak acid, so lower pH value but higher than bases)
RbNO3  (neutral, 7) 
RbOH    (?)
HNO3    (large Ka, so small pH value)
HONH2 (?)
RbOBr (salt, from Rb+ and OBr-)

I have:
HNO3 < HOBr < RbOBr < HONH3NO3 < RbNO3 < HONH2 < RbOH
I don't know the Ka values or the pH for some of them, so maybe someone can help me complete the ranking?

DrBob222 · Answer

HONH2 is hydroxyl amine with Kb = 1.1
RbOH is a strong base so 0.1M gives 0.1M OH or pOH or 1 (pH of 13)
RbOBr is a salt so the pH is determined by the hydrolysis of OBr^-
OBr^- + H2O ==> HOBar + OH^- You can do an ICE chart on this and determine the pHknowing the Ka of HOBr. You can look that up on Google.