We have discussed on the strategies to predict the products of electrolysis of molten compounds as electrolytes in the earlier post.

Today, we are going to examine the Strategies to Predict the Products of Electrolysis for Aqueous Solutions.

For aqueous solutions, there is more than 1 type of cations and anions, since water is present.
Water will contribute to H+ and OH- ions in addition to the ionic compound that is present.

When more than one type of cations or anions are present in a solution, only 1 cation & 1 anion is preferentially selected for discharge.

The selectivity discharge of ions depends on 3 factors:
1. Position of metal in the reactivity series
2. Concentration of the ion in the electrolyte
3. Nature of the electrode used

Let’s check out on the 1st Criterion to consider – Position of Metal in Reactivity Series

Ease of Discharge of Cations Increases down the list:

Potassium Ion, K+
Sodium Ion, Na+
Calcium Ion, Ca2+
Magnesium Ion, Mg2+
Aluminium Ion, Al3+
Zinc Ion, Zn2+
Iron Ion, Fe2+
Lead Ion, Pb2+
Hydrogen Ion, H+
Copper Ion, Cu2+
Silver Ion, Ag+

Ease of Discharge of Anions Increases down the list:

Sulphate Ion, SO42- (Do not discharge)
Nitrate Ion, NO3- (Do not discharge)
Chloride Ion, Cl-
Bromide Ion, Br-
Iodide Ion, I-
Hydroxide Ion, OH-

As such, Cu2+ is preferentially discharged @ the -ve cathode, if we have Cu2+, H+ and Fe2+ in aqueous solutions.

And for anions in aqueous solutions, we will have OH- ions preferentially discharged over NO3- and Cl- if we have all of them in the solutions.

So far so good? Let’s check one of question:

Question 1:

If we have a soluton of dilute aqueous NaCl solution and inert platinum electrode is being used,

(i) What ions are present in the electrolyte?

(ii) What are the products @ the cathode and the anode?

PS: Leave us your suggested answers directly below this post at “Leave Your Reply” section.

I hope you have been learning something so far. =))

Up next, we will visit the 2nd Criterion for predicting the products of electrolysis:
“Concentration of Aqueous Solutions”

PPS: I am launching a book called “Up Your Chemistry Grades Now!” in ebook version before i send it to publisher for the hardcopy book to be available in majoy bookstores.  As it takes sometime for the hardcopy book to be published, i want to ensure graduating students sitting for major examination soon, will have a chance to get hold of this wonderful book that i have compiled over 10 years of Chemistry Coaching. It includes all the Common Errors and Misconceptions that many students made batch after batch, and the Correct Essential concepts you need to know .  Also included are the Definitions that you need to know in O Level Chemistry Exams and also Tips on what the Examiners are Looking For. If you studying very hard for your Chemistry but yet to score the marks that you truly deserve, make sure you are the first to have your hand on it. You can sign-up for more information on the launch of this wonderful book here.

Related Articles: