1) Which ion(s) below would undergo hydrolysis in water?
A) Cl-
B) K+
C) NH4+
D) NO3-
E) Two of the above
My guess is C, but I'm not too sure about this one.
2) Calculate the [OH-] present in solution labeled 1.73 M methylamine. CH3NH3 + H2O --> CH3NH3+ + OH-.
I get 2.76 x 10^-2 for this, but again, not entirely sure.
NH4^+ is the only one hydrolyzed. You know NO3^-, Cl^- and K^+ are not hydrolyzed BECAUSE those hydrolysis products would be STRONG acid/bases. For example,
Cl^- + HOH ==> HCl + OH-
or
K^+ + HOH ==> KOH + H^+
and that doesn't happen. Why NH4^+? BECAUSE it forms a WEAK base.
NH4^+ + H2O ==> NH3 + H3O^+ and that is why solutions of NH4Cl and the like are acidic in solution.
Acetate ion is hydrolyzed because it forms a WEAK acid.
C2H3O2^- + HOH ==> HC2H3O2 +OH^- and that's why solution of sodium acetate or potassium acetate are basic in solution.
I'll post later on #2.
You made a typo in th equation. It should be
CH3NH2 + HOH ==> CH3NH3^+ + OH^-
I obtained 2.9E-2 for OH^- but we may not have used the same Kb. I used 5E-4.
Right. I typed it correctly, so it's definitely a typo on the worksheet. Thanks for pointing that out.
I used 4.4 x 10^-4 for Kb, per my textbook.
Thanks for checking!
1) To determine which ions would undergo hydrolysis in water, we need to consider their behavior. Hydrolysis is a chemical reaction between a compound and water, resulting in the formation of an acidic or basic solution. In this case, we are looking for the ions that would react with water to produce either H+ (acidic) or OH- (basic) ions.
A) Cl-: Chloride ions do not undergo hydrolysis. They are the conjugate base of a strong acid (HCl) and do not react with water to produce H+ or OH- ions.
B) K+: Potassium ions also do not undergo hydrolysis. They are the conjugate base of a strong base (KOH) and do not react with water to produce H+ or OH- ions.
C) NH4+: Ammonium ions (NH4+) do undergo hydrolysis. They react with water to produce H+ ions, making the solution acidic.
D) NO3-: Nitrate ions (NO3-) do not undergo hydrolysis. They are the conjugate base of a strong acid (HNO3) and do not react with water to produce H+ or OH- ions.
Based on this analysis, the correct answer is E) Two of the above, with options C (NH4+) and D (NO3-). Therefore, your guess of C is correct.
2) To calculate the concentration of hydroxide ions ([OH-]) in solution, we need to use the given equation CH3NH3 + H2O --> CH3NH3+ + OH-. We need to determine the amount of CH3NH3 that has reacted in order to calculate the concentration of OH-.
Assuming the reaction has gone to completion, we can use the stoichiometry of the reaction to determine the concentration of OH- ions. From the equation, we know that one mole of CH3NH3 reacts to produce one mole of OH- ions.
Given that the concentration of methylamine (CH3NH3) is 1.73 M, the concentration of OH- ions will also be 1.73 M.
Therefore, the correct concentration of OH- ions in solution labeled 1.73 M methylamine is 1.73 M, not 2.76 x 10^-2.