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
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.
To predict whether aqueous solutions of salts are acidic, basic, or neutral, we need to consider the types of ions present in the salt and their interactions with water. Let's analyze each salt:
a. Potassium perchlorate, KClO4
Potassium perchlorate dissociates into potassium ions (K+) and perchlorate ions (ClO4-) in water. Neither of these ions reacts with water, so the solution is neutral.
b. Sodium benzoate, C6H5COONa
Sodium benzoate dissociates into sodium ions (Na+) and benzoate ions (C6H5COO-) in water. The benzoate ions can react with water, accepting a proton (H+) to form a weak acid, benzoic acid (C6H5COOH):
C6H5COO-(aq) + H2O(l) ⇌ C6H5COOH(aq) + OH-(aq)
Therefore, the solution of sodium benzoate is slightly basic.
c. Chromium(III) nitrate, Cr(NO3)3
Chromium(III) nitrate dissociates into chromium(III) ions (Cr3+) and nitrate ions (NO3-) in water. The nitrate ions do not react with water, so they do not affect the acidity or basicity of the solution. However, the chromium(III) ion can undergo hydrolysis to form an acidic solution:
Cr3+(aq) + 3H2O(l) ⇌ Cr(OH)3(s) +3H+(aq)
Due to the hydrolysis of chromium(III) ions, the solution of chromium(III) nitrate is acidic.
In summary:
a. Potassium perchlorate, KClO4: Neutral
b. Sodium benzoate, C6H5COONa: Slightly basic
c. Chromium(III) nitrate, Cr(NO3)3: Acidic
To determine whether the aqueous solutions of the given salts are acidic, basic, or neutral, we can look at the ions they produce when dissolved in water.
a. Potassium perchlorate, KClO4:
When dissolved in water, KClO4 dissociates into K+ and ClO4- ions. Neither of these ions reacts with water to produce any acidic or basic species. Therefore, the solution of potassium perchlorate is neutral.
b. Sodium benzoate, C6H5COONa:
When dissolved in water, C6H5COONa dissociates into Na+ and C6H5COO- ions. In this case, the C6H5COO- ion can react with water as follows:
C6H5COO-(aq) + H2O(l) → C6H5COOH(aq) + OH-(aq)
In this reaction, the C6H5COO- ion acts as a weak base by accepting a proton from water to form benzoic acid (C6H5COOH) and hydroxide ions (OH-). Therefore, the solution of sodium benzoate is basic.
c. Chromium(III) nitrate, Cr(NO3)3:
When dissolved in water, Cr(NO3)3 dissociates into Cr3+ and NO3- ions. Neither of these ions reacts with water to produce any acidic or basic species. Therefore, the solution of chromium(III) nitrate is neutral.
In summary:
a. Potassium perchlorate solution: neutral.
b. Sodium benzoate solution: basic.
c. Chromium(III) nitrate solution: neutral.