What are Displacement Reactions?

Co-authored by Kera B

What are the uses of displacement reactions?

A displacement reaction occurs, $A+BC\to B+AC$. Hence, the applications of displacement reactions can be seen in thermite welding, iron extraction, metal extraction, and acid indigestion. Note: Displacement reactions are also used to displace metals from their aqueous salt solutions.

Why letting the students figure out the chemical reactions after they observe a demo, or do the experiment in the chemistry lab is the way to go?

This is part of my ongoing experimentation on how to deliver chemistry topics to students in a more engaging and contextually relevant way.

I was inspired by chemist Philip Cook’s demo on Twitter, and decided to test it out with my Innovations in Chemistry class which I am prototyping and co-designing with some students at Marymount School of New York.

I prepared a similar set-up for my students, first of all, I did the demo, then I let them do the experiment themselves.

I lined up all of the chemicals necessary for the reactions and then we went to work. Then I asked them to figure out all of the reactions that just happened.

Here is a list of the chemicals we encountered doing these experiments:

Water — H2O

Sodium Hydogencarbonate — NaHC03 (buffer)

Phenolphthalein (indicator) — C20H14O4

Barium Chloride — BaCl2

Potassium Dichromate — K2Cr2O7.

Hyrochloric Acid — HCl

Below are the structures for all of the reactants and products that went on in all of these reactions:

What happens when we add Sodium bicarbonate to water?

What happens when we add Phenothalein to the buffer solution?

What happens when we add the “pink” solution to the solution of barium chloride?

What happens when the milky solution is added to the solution of potassium dichromate?

Letting students figure out the reactions for themselves instead of giving them the reactions will ensure a better understanding of what is going on. Also giving the students the structures of the chemicals also helps them with balancing the equations. I say demo first and figure out the chemistry later.