There are two ways to do this. There is a right way, which in my opinion is hard to understand, and the wrong way chemistry wise BUT in my opinion much easier to understand AND the wrong way gets the correct answer anyway.. So here's the right way.
You must know which ion is the stonger acid or base. Write the equation for that ion in reacting with water. It works this way.
KClO4. Both K^+ and ClO4]^- are weak bases/acids and will not react with water. Therefore, a solution of KClO4 is neutral.
C6H5COONa. Na ion is a weak base and will NOT react with water BUT C6H5COO^- is a stronger base than H2O and will react with water like this.
C6H5COO^- + HOH --> C6H5COOH + OH^-. The OH^- tells you the solution will be basic.
Cr(NO3)3. The NO3]^- is too weak to react with water but Cr^3+ is a srrong enough acid to react this way.
Cr^3+ + 6H2O --> Cr(H2O)6]^3+ and that reacts with H2O this way:
Cr(H2O)6]^3+ + H2O ---> Cr(H2O)5(OH)]^2+ + H3O^+. and the solution is acid. Actually this continues stepwise until you have Cr(H2O)3(OH)3]
So a is neutral, b is basic and c is acidic in solutions.
The fastidious will argue with showing the wrong way but still getting the right answer; however, few students know that K and ClO4 ions are too weak, that the C6H5COO^- is strong enough to attact a H+ from water but Na is too weak to attract an OH ion etc. So here is what I did until I knew enough chemistry to do it th right way. I write the hydrolysis equation in full.
KClO4 + HOH ==> KOH + HClO4.
C6H5COONa + HOH ==> C6H5COOH + NaOH
Cr(NO3)3 + 3HOH ==> Cr(OH)3 + 3HNO3
#1. KOH is a STRONG base. HClO4 is a STRONG acid. neutralize each other. so neutral.
#2. C2H5COOH is a weak acid. How do you know that? It has a Ka. So you have a WEAK acid and a STRONG base(NaOH). So you know the solution will be basic because NaOH makes it that way.
#3. Cr(OH))3 is a WEAK base (actually it is a ppt but it has a K value). HNO3 is a STRONG acid so the solution is acid.
Hope this helps.
Predict whether aqueous solutions of the following salts are acidic, basic, or neutral, and
write an equation for the reaction of any ion with water.
a. Potassium perchlorate, KClO 4
b. Sodium benzoate, C 6 H 5 COONa
c. Chromium(III) nitrate, Cr(NO 3 ) 3
1 answer
1 answer