The Science Teacher October 2005, p. 54-58
A Year Without Procedures
Lisa Backus
Most high school chemistry labs contain detailed procedures on how to perform experiments, collect data, and analyze findings. These step-by-step instructions often eliminate opportunities for inquiry, higher levels of thinking, and the sense of accomplishment students find through independent discovery.
For these reasons, two years ago I elected to remove specifically outlined procedures from many chemistry labs in my classroom. By doing so, I promoted collaboration between students as they designed their own steps and illustrated that more than one way exists to solve a problem. I challenged students and let them experience the scientific process and the reward of discovering answers on their own. This article describes a chemistry-based experimental year without procedures, but the concept can be applied to any scientific discipline.
Reviewing the procedures
Before introducing inquiry-based labs, I began by examining many of the current labs scheduled for our chemistry class. Could students be successful doing the lab without the procedures? Did they have enough background information? Would it be safe? I found that many labs could be done successfully without detailed procedures; summary descriptions of these labs are provided in Figure 1).
Figure 1. Labs without procedures.
Always wear safety goggles and follow proper safety guidelines.
*These were the chemicals given as part of the lab. For some of the labs students requested additional chemicals, depending on their own procedures. Some of the most common chemicals requested are listed in italics in parentheses.
Lab
Question/problem posed
Chemicals*
Background information prior to lab
Student responses
1
Describe as thoroughly as possible your unknown chemicals.
Al shot, vinegar,
1 M HCl, corn syrup,
Zn shot, 1 M NaOH,
CaCO3(s),
0.1 MNa2SO4,
0.1 M BaCl2,
CuSO4•5H2O (s),
NaCl(s),
sodium polyacrylate(s),
citric acid(s), SrCl2 (s),
sand and distilled H2O
General science experiences. Under-standing of laboratory safety rules.
Characterized samples by appearance, solubility in water, odor, color, viscosity, density, reaction with each other, etc.
2
Identify your metal using density (a list of possible choices are given). A detailed example of this lab is given in Figure 2.
Al shot and Zn shot from above lab
Most had some experience with density.
Most found volume by water displacement and mass on a balance. Used handbook of chemistry and physics or chemical dictionary to identify metals using the density.
3
Which materials are soluble in water and are there any patterns?
(NH4)2SO4,
Ca(C2H3O2)2,
CaCl2, CoSO4,
Cu(C2H3O2)2,
MgSO4,
KBr, NaC2H3O2,
Na2SO4, NaCl,
SrCl2,
Ca(NO3)2, KNO3,
LiNO3, CaCO3,
BaCO3, MnO2,
CuCO3,
CuO, ZnO
General knowledge of solubility.
Class discussed how much of each sample (same mass or volume), how much water, and how long to stir.
4
Identify the unknown solution from a list of possibilities (NaCl,
Na2SO4, Co(NO3)2,
Pb(NO3)2, K2CrO4,
Na3PO4,
BaCl2, CuCl2,
AgNO3).
Unknowns from first lab,
0.1 M Na2SO4
or 0.1 M BaCl2
marked as letters
[0.1 M of AgNO3,
K2SO4,
Ba(NO3)2,
FeCl3, Na3PO4,
NaCl]
Previous lab examined what chemicals formed precipitates when mixed.
Students used precipitation reactions and results from previous lab as a process of elimination. (Using spot plates and microscale amounts makes this more manageable.)
5
What products are formed when baking soda is heated?
NaHCO3
Students given a brief background on baking soda and three possible equations.
Students had already learned how to solve mole-related stoichiometry problems.
Students heated small amounts of baking soda and weighed material afterwards. Discussions revolved around how much baking soda to use, how long to heat it, how it could be heated safely, and how to perform calculations.
6
Determine how temperature affects the solubility of KNO3.
KNO3
Previous labs involving solubility.
Students debated how to keep uniform temperature and how to measure the amount of solid that dissolved.
7
What is the concentration of the copper sulfate solution?
0.068 M CuSO4
Students previously made and saved solutions of known concentrations (0.2 and 0.1 M CuSO4).
Students made standards of known concentration and compared the colors, others evaporated their solution, and one group formed and weighed a BaSO4 precipitate.
8
How much energy is released per mole of candle wax when it burns?
A candle
The night before this lab, students were told to find the definition of a calorie. Previously, students calculated heats of reaction from bond energies and used joules.
Students placed water over a flame and measured increase in temperature and loss of candle mass. Discussions centered on how much water to use, how to place the water above the flame, and how to avoid heat loss.
9
Determine and graph the quantitative gas relationship between one of these pairs—P and V, V and T, or P and T (keeping other variables constant).
None given
Students had just done exploration involving qualitative observations of these variables.
Students performed a variety of tasks. They used balloons, flasks, thermometer, syringes, and pressure gauges.
10
Calculate the heat of solution for four different solids (J/g)
KNO3, CaCl2,
NH4Cl, NaCl
Students familiar with heat being absorbed or released during reactions and changes of state.
Students measured mass of solid, placed it in water, and measured temperature change. Different quantities were used. Too much water or too little solid gave small temperature changes.
11
Determine and measure two factors that will affect the reaction rate.
One solution labeled A with 0.02 M KIO3
another solution labeled B with 4 g starch,
2 g NaHSO3, and
5 ml of 1 M sulfuric acid per liter
Students were given a clock reaction to first observe before they made changes.
Students changed temperature, degree of mixing, and concentration of one of the reactants.
12
What properties do acids have in common? What do bases have in common? Do all acids react the same?
1 M HCl,
1 M HC2H3O2,
1 M NaOH,
1 M KOH, 6 M HCl,
6 M HC2H3O2,
1 M NH4OH,
1 M H3PO4
Previous general knowledge.
Students remembered acid litmus and pH paper tests, reaction with metals, and reaction with baking soda.
To address safety, students were instructed at the beginning of the year on general chemical safety procedures and given a safety contract to read and sign. Prior to each lab, special reminders were given regarding specific chemicals; however, because these chemicals and their uses could change based on students’ ideas, I required that all procedures be cleared with me before implementation. This procedure review gave me a chance to check for possible safety issues and question student lab design, although I did not usually correct student procedures unless they were unsafe.
Reviewing lab designs also kept me busy during lab periods. Instead of providing and correcting procedures, I posed questions or problems to solve, and left it up to students to figure out the experimental steps. To develop procedures and conduct experiments, students typically brainstormed and worked in groups of four, although occasionally they worked in pairs and a couple of times as a whole class.
Implementing inquiry
The opening lab
For Lab 1 (Figure 1), I gave students 16 substances—liquids, solutions, and solids—and asked that they describe the substances as thoroughly as possible, including differences and similarities. I intentionally provided a variety of chemicals that had different densities, colors, and odors, and that would change colors, produce precipitates, bubble, or solidify when mixed. This opening lab acted as a springboard for our unit on how chemists identify unknowns.
In addition to visually observing the substances, students chose to examine solubility in water, melting points, odor, reactions in flames, and reactions with combining samples. Students were required to check with me before doing anything beyond visual observations and prior to disposal (I required a disposal check for each lab). If students needed supplies or chemicals to examine substances, they had to ask for these materials. I did not want to influence student choices by setting out particular supplies, such as Bunsen burners.
After obtaining my safety approval, students who chose to put materials in the flame were surprised when one material turned red (strontium chloride) and others were perplexed when they added water to a white powder and it solidified (sodium polyacrylate). Several times during the lab, students excitedly showed me their findings.
Over the next several labs, students proceeded to identify several of these 16 substances. To identify the first two, aluminum and zinc, density was used. I decided that determining density (Lab 2, Figure 1) was a formal lab procedure students could design on their own (Figure 2).
Figure 2. Density inquiry lab without procedures example. (Taken from Figure 1, Lab 2.) Editor’s note: Although various standard density lab procedures are available, students achieve a deeper understanding of the concept of density if they develop a procedure on their own. See the bottom part of this figure for an online-only example.
I. Introduction
The purpose of this lab is to identify two unknown elements (A and E) from their densities.
II. Investigation
Decide how to determine the density of your materials. You may discuss your plan in groups of four, but each lab pair must analyze their own material. Before doing anything, have the teacher OK your procedure for safety. Write your procedure in your lab notebook.
III. Data
Record your data in your lab notebook in an organized fashion.
IV. Results
Calculate the density of the material. Show your work in your lab report.
V. Analysis questions
Record your responses in your lab report.
a. From the list of possibilities, using reference materials, determine the possible identity of your unknown. From the list of possibilities (Co, Al, Cd, Ni, W, Zn, Ir, Pt), determine the identity of your unknown . Defend your choice. What additional information would increase your confidence in your identification?
b. Assuming you have correctly identified your material, what is your percent error? Is your error small enough to give you confidence in your identification?
c. What could have contributed to the error?
d. Examine your procedure. List all improvements you would make if you conducted the experiment.
e. How is density important in everyday life? List as many applications as you can.
Online Extension
A density inquiry lab with procedures.
I. Introduction
The purpose of this lab is to measure the density of an unknown metal (e.g., A or E) and to use this density to determine its identity. Density is a measure of an object’s mass per unit volume and is determined by dividing the mass of an object by its volume: ñ=m/v.
II. Procedure
1. Obtain 20 pieces of your metal.
2. Determine the mass of the pieces by placing a weighing dish on the balance. Push the tare button. The balance should read 0.00 g. Place the metal pieces in the dish. Read the mass and record in your data table. Record to the nearest 0.01 g.
3. Measure out 10.0 mL of water using a 25 mL graduated cylinder. Record this initial volume in your data table.
4. Add the metal to the graduated cylinder. The water level should rise.
5. Measure the new water level. Record the volume to the nearest 0.1 mL in your data table.
6. The amount that the water rises is equal to the volume of the metal pieces added. Subtract the initial water volume (step 3) from the final volume (step 5) and record in your results table.
7. Divide the mass of metal (step 2) by the volume (step 6)
8. Compare the density obtained to the list of choices.
III. Data
Unknown letter
Mass (g)
Initial volume (mL)
Final volume (mL)
A
E
IV. Results
Unknown letter
Volume of metal (mL)
(Final – Initial volumes)
Density of metal
Mass/volume (g/mL)
A
E
V. Analysis questions
1. From the following list of possibilities, determine the identity of your unknown. Defend your choice.
Metal
Density (g/mL)
Cobalt
8.75
Aluminum
2.70
Cadmium
8.65
Tungsten
19.6
Zinc
7.14
Nickel
8.80
Iridium
22.4
Platinum
21.4
2. What is your percent error?
3. What could have contributed to the error?
4. How is density important in everyday life? List as many applications as you can.
Designing density procedures
Because most students already had some familiarity with density, removing the procedure created a need for them to make connections with prior knowledge (Figure 2). Discussions centered on student recollection of the density formula: Was the formula, mass divided by volume or volume divided by mass? How should the volume of the metal pellets be measured?
As students approached the problem, some groups tried putting just the pellets in a graduated cylinder, but quickly decided that the air between the particles was taking up some of the volume. In the end, to determine the volume most students had success using water displacement in a range of containers and various amounts of material. The range of values obtained led to an informative post-lab discussion on accuracy and precision in measurements.
After finding the density, students were asked to identify their metal from a list of possibilities. I did not show them where to find this information; some students searched the internet, while others looked in reference books.
Determining heat of reaction
As the year progressed and topics became more novel, I had to make sure students received the proper background information necessary for successful labs. Occasionally, prior to conducting labs, I would assign related homework to give students exposure to the knowledge needed. Often, though, I used the lab to introduce new concepts that were then further developed in class discussions following the lab.
For example, one lab involved having students determine the amount of heat given off per gram of burning candle wax (Lab 8, Figure 1). At first, students wanted to use some type of meter that would measure heat directly and were puzzled when I told them that such an instrument was not available. For homework the night before the candle-wax lab, students had been asked to find the definition of a calorie (students were already familiar with joules). The first successful group decided to place water over the candle and measure the temp-erature rise in order to calculate heat. This group was the first to make the connection between their homework and the lab.
Other lab groups developed similar procedures with variations in the amount of water, the position of the water above the flame, and the time the candle burned. Postlab discussions focused on how to minimize heat “loss” to the environment, and how this affected the accuracy of the lab.
Gas law labs were my personal favorites of the year (Lab 9, Figure 1). Every group designed distinctly different procedures. Students worked with ice, balloons, eudiometers, syringes, and pressure gauges to discover the relationship between two variables (P and T, T and V, or P and V).
For example, one group examining V and T put a thermometer inside a flask and a balloon on the top of the flask. They varied the temperature by placing the flask in the refrigerator and then into different hot water baths (the balloon was not submerged). At each temperature, volume was measured as the combination of the volume of the flask and the volume of the balloon (which students assumed to be close to spherical). Afterward, students graphed results and even discovered information on absolute zero.
Assessment
During all of the experiments in Figure 1, students were required to keep an accurate account of their analyses in a lab notebook, including a table of contents, title, purpose, individual procedures, and data.
Using a grading rubric, students swapped notebooks (not with their lab partner) and critiqued each others work, then critiqued their own. Criteria included the ease with which someone could duplicate the student’s lab based only on the descriptions in the procedures, and how appropriately and thoroughly data was recorded. After the student critiques, I also assessed the notebooks. Students were usually very honest and accurate with their comments.
In addition to the lab notebook, students wrote lab reports that included results, conclusions, and questions. I often graded these myself. For some of the labs, students were assessed on accuracy (i.e., did they identify the unknown?). In most cases, however, students demonstrated understanding through designing successful procedures and analyzing their results thoughtfully.
Obstacles and rewards
As expected, the labs were not as time efficient without procedures. Many labs took more planning time. Labs with defined procedures had been refined over the years to take out all the “kinks.” By removing the procedures, I put many of the kinks back in, adding more time to the lab or sometimes creating ambiguous results.
These issues led to great discussions on how to improve the labs and insight on creating good lab procedures. For example, after discussing student errors with temperature in the rates of reaction lab, students repeated the experiment using their classmates’ suggestions. In hindsight, I wish I had done this for a few more of the labs (e.g., the candle wax lab and solubility with temperature). Students were eager to make improvements and produce more meaningful results; I was surprised by this enthusiasm to repeat a lab. By interpreting ambiguous results and refining experimental procedures, students achieved a much better understanding of the nature of science.