It is my humble opinion, based on 36 years of teaching high school chemistry, that 11 Chemistry must start with a look at Chemical Reactions, for the simple reason that this begins the student’s formal study of chemistry with an empirical focus.
On Day 1, I have my students perform an investigation to determine the relative atomic mass of Mg to Zn using single displacement reactions.1 How’s that for an empirical—and quantitative—start?!? Students obtain, precise—and correct(!) to two significant digits—the relative atomic (molar) mass of Mg : Zn, while carrying out single displacement reactions and reviewing the Activity Series.
I digress. See A Super-Engaging Way to Start 11 Chemistry here on ChemEd X if you would like to find out more about that activity.
As the unit progresses, students will likely see several engaging teacher demonstrations, including, I hope, the reaction of sodium metal with water:
Na(s) + HOH(l) → NaOH(aq) + H2(g) (1)
This reaction provides deeper insight into the Activity Series. Students observe bubbles of a gas; they may even see the gas ignite as H2(g) reacts with O2(g) in the air. I perform several tests on the resultant solution to prove that NaOH(aq) is produced:
- Use a conductivity apparatus to show that there is a dissolved ionic compound (NaOH) present;
- Carry out a flame test to show that Na+ ions are present;
- Use phenolphthalein to indicate that the solution is basic.
And so the products are proven empirically.
My students do at least one more important laboratory activity, entitled “From Copper to Copper”, or “the Copper Cycle”, or “Give Me Back My Copper”. I refer the reader to the excellent version of "Give Me Back My Copper!" by Allison Tarvin, available on ChemEd X.
This laboratory activity has students carry out the following reactions. (Reactants and products are color-coded for an obvious reason.):
Cu(s) + 4 HNO3(aq) → Cu(NO3)2(aq) + 2 NO2(g) + 2 HOH(l) (2)
(This should be done as a teacher demonstration for safety.)
The blue-coloured aqueous solution of Cu(NO3)2 is given, in a small beaker, to students.
They carry out the following reactions sequentially, in that same beaker. This activity is qualitative; the point is the observation of the different products.
Cu(NO3)2(aq) + NaOH(aq) → Cu(OH)2(s) + NaNO3(aq) (3)
Copper II hydroxide is a blue precipitate
Cu(OH)2(s) + heat → CuO(s) + HOH(l) (4)
Copper II oxide is a black precipitate
CuO(s) + H2SO4(aq) → CuSO4(aq) + HOH(l) (5)
Copper II sulfate(aq) is blue
CuSO4(aq) + Zn(s) → ZnSO4(aq) + Cu(s) (6)
Zinc sulfate(aq) is clear and colourless; students observe spongy copper(s)
And so metallic copper is regenerated after these five reactions:
(2) synthesis (redox, really)
(3) double displacement
(5) double displacement
(6) single displacement
My students have carried out these reactions; they have seen the products first-hand.
The Capstone Demonstration
On the final day of the Chemical Reactions unit, I write the following on the board—and ask students to predict the product(s).
Na(s) + CuSO4(aq) → ??? (7)
Many will fall prey to a knee-jerk response and suggest that Na will simply displace Cu to produce Na2SO4(aq) and Cu(s).
Then I ask my usual question: “How can we test this”?
— Tommy Technetium (@pchemstud) July 29, 20231
And so I drop a piece of Na into a shallow petrie dish of 1 M CuSO4(aq), which you and I know is primarily water. As you can see in video 1, there is an immediate exothermic reaction with water (1); the hydrogen produced reacts with oxygen in the air and ignites (8).
H2(g) + ½ O2(g) → HOH(g) + energy (8)
But there’s more: The NaOH produced in (1) reacts with CuSO4 in the solution to produce a light blue precipitate of Cu(OH)2 (3). And the heat from the combustion of hydrogen gas (8) causes at least some of the just-formed Cu(OH)2(s) to decompose into a black precipitate of CuO (4).
Figure 1. After the reactions, note the light blue aqueous solution of CuSO4, the blue precipitate of Cu(OH)2, and the black precipitate of CuO. Placing the Petrie dish atop a white background will facilitate observation of the products.
With appropriate questioning, students identify the products of the reaction. They admit— sheepishly—that the reactions were observed in the “Give Me Back My Copper” lab, and that the answers to my original question (7) were within their ability.
- Carry out the demonstration in a shallow Petrie dish. If beaker is used, H2(g) may accumulate before it ignites, causing the beaker to explode
- Practice the demonstration beforehand with no students present
- Carry out the demonstration in a fume hood, or at least behind a safety shield with students well back
You are invited to peruse the student-ready handout, available as Supporting Information. (Log into your ChemEd X account to access. Don't have an account? Register here for free!) The handout can be used without performing the demonstration; I used it when teaching over Zoom. I invite you to make the necessary changes to suit your teaching.
1 mol/L CuSO4(aq)--I typically fill a 10cm Petrie dish about half-full--about 50 mL.
I use roughly a pea-sized piece of Na(s). When the teacher tries this demo before class, he or she can make minor adjustments as needed.
Plan to perform this inside of a fume hood or behind a safety shield.
- Thanks to Tom Kuntzleman, of Wayne State University—and an associate editor for ChemEd X—for recording me performing this demonstration at ChemEd 2023, at the University of Guelph. Tommy Technetium (@tommy.technetium) • Instagram photos and videos
For Laboratory Work: Please refer to the ACS Guidelines for Chemical Laboratory Safety in Secondary Schools (2016).
For Demonstrations: Please refer to the ACS Division of Chemical Education Safety Guidelines for Chemical Demonstrations.
Other Safety resources
RAMP: Recognize hazards; Assess the risks of hazards; Minimize the risks of hazards; Prepare for emergencies