Reactions of Metals Lab
Lesson 7 of 13
Objective: SWBAT work safely in lab to observe metals and nonmetals becoming ionic compounds
This lesson addresses the following NGSS standards:
- HS-PS1-1: Use the periodic table as a model to predict the relative properties of elements based on the patterns of electrons in the outermost energy level of atoms. Students will be making Lewis dot diagrams of the elements in the reactions to determine whether they will gain or lose electrons to satisfy the octet rule.
- HS-PS1-2: Construct and revise an explanation for the outcome of a simple chemical reaction based on the outermost electron states of atoms, trends in the periodic table, and knowledge of the patterns of chemical properties. Students will use their Lewis dot diagrams to predict whether elements will gain or lose electrons, and the flow of electrons between reactants.
- Science and Engineering Practice 3: Planning and Carrying Out Investigations. Students will carry out a multi-part lab investigation.
- Stability and Change Cross Cutting Concept: Much of science deals with constructing explanations of how things change and how they remain stable. Students will use Lewis dot diagrams to predict how elements will gain or lose electrons to become more stable ions and satisfy the octet rule.
I cobbled this lab together from common reactions to focus in on element to ion reactions. This is a difficult concept for students to grasp, so providing some concrete visuals is helpful. To help students connect the lab reactions to the content, they will record all their data and conclusions in each part of the experiment. I find separate data tables and analysis sections to be confusing for my students who mix up which reaction was which and where to record it.
Due to the fact that I teach chemistry in two different rooms and alternate between the rooms three times in the day, I decided to make this portable by creating lab boxes. If I were doing this lab in one class all day, I would strongly consider doing this lab in stations, as it makes the cleanup much simpler.
Lab box contents:
- Book of matches
- Aim and Flame style lighter
- Flint striker
- Small bottle with magnesium strips
- Crucible tongs
- Small bottle with lump sulfur
- 2cmx2cm square of copper foil
- Small piece of steel wool
- Piece of aluminum foil
- 50mL dropper bottle containing .25M copper (II) chloride
- 10mL graduated cylinder
- Small bottle with mossy zinc
- 50mL dropper bottle containing .1M hydrochloric acid
On each lab table:
- Ceramic tile
- Distilled water bottle
- Test tube rack with small test tubes
- Waste beaker
- Bunsen burner
When students enter the room, I have on the board "Get out your lab sheet from yesterday." I take attendance quickly while students are getting out their lab paper.
Once students are ready, I remind them of our safety acronym: "GAS" which stands for Goggles, Apron, Standing. I remind them to be careful about having the gas off when they aren't using the bunsen burners, to rinse off if they spill any chemicals on themselves, and that I expect focused behavior while doing the lab.
I hold up one of the waste beakers to show them where to dispose of chemicals, and ask if there are any questions. Usually the questions do not come out until they are engaged in the lab. I remind them to use their help cards if they get stuck and it is not an emergency. I then invite them to suit up and enter the lab space.
One thing I always have on hand are cheap hair ties. So much of the lab safety rules regarding clothing are opposite of fashion, particularly for female students. I try to accommodate as much as possible for forgotten hair ties, fluffy sleeves and the like. However, I have not gone as far as some local schools by getting shoes from resale stores for students. I have offered surgical booties for students in open toed shoes though.
Student Lab Work
While students are working, I circulate the lab to comment on results, reinforce safety rules, and answer student questions. The first 3 minutes are usually reminding students to stay standing and to wear the goggles over their eyes. I show students how to open the vents on the goggles to make them more comfortable.
In Part 1: Bunsen Burner Lighting, many of the students have difficulty using the flint strikers. They don't pull up and across, so they don't get a spark. I show students how to properly position their thumb and fingers to make it more natural. Many students are also afraid to use the matches, so I demonstrate how to hold with their thumb and middle finger, using the index for pressure on the friction strip.
During Part 2: Reaction of Magnesium metal with Oxygen gas, students generally do just fine, excepting they stare into the bright white flame. The biggest challenge here is distinguishing the excitement from any possible lab accident concerns. As I walk around, I make sure students are recording their observations correctly.
During Part 3: Reaction of Copper metal with solid Sulfur, students have a hard time identifying the copper and the steel wool. Once they do, the only procedural issue is not pressing hard enough with the sulfur to get a good reaction.
In Part 4: Reaction of Aluminum metal with aqueous Copper (II) chloride, students again have difficulty identifying the chemicals from the box. This is an excellent chance to refine observation skills and use the vocabulary from the day before, describing the aluminum as "lustrous" instead of "shiny". We also focus on precise language in the chemical change, avoiding terms like "rusting" when describing the elemental copper formation.
In Part 5: Reaction of Zinc metal with aqueous Hydrochloric acid, students can be gunshy about working with the acid. When I see this I explain that the acid is a weaker mixture of the same acid in their stomach. This helps allay student fears. Students do a better job of observing here, but can miss the heat generated by the reaction, so I encourage them to touch the test tube, and when they notice it, they generally go back and check the aluminum reaction for heat also. The zinc in this video had a coating of oxidation, so the bubbling is very slow. Fresh zinc works much better for the reaction. Better to buy small quantities each year than a large bin for the long term.
If students finish lab early, they clean up and return to their seats to work on any parts they skipped, such as creating the Lewis dot diagrams in each step.
As students are finishing, I compliment them group by group about their work and clean up. If groups need to clean up better, I send them back to finish and make sure the lab is neat.
I give students the option of turning in the completed lab sheet now if they feel it is complete, or to take it home to finish their Lewis dot diagrams and predictions.
As this is our first wet lab of the year, I assure any groups who didn't finish that they will have the opportunity to come after school if needed, and schedule that with students who need it.
When assessing the student work, I am focused on their observations and predictions as to which element will gain/lose electrons. Although I do not use the term redox with regular chemistry, essentially these are all redox reactions, something my AP students struggled with. I am especially looking for consistency on students labeling the metals as losing electrons, as we discussed this as a key characteristic of metals in yesterday's notes. Many students did not get this pattern down, so I believe the changes our literacy coach and I came up with will help draw this out more next year.
This lab could have been better with a whole class debrief the following day before beginning the Atoms and Ions lesson. Re-focusing and connecting the lab content with the daily content is something I continue to work on as a teacher. These connections help the students follow the flow of ideas through the class, and sometimes as the content expert who already sees the connection, we forget to make it more explicit for the kids.