high school chemistry labs by marcusbuggs

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									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
     Removing procedures specifically outlined procedures from many chemistry labs
       from chemistry labs in my classroom. By doing so, I promoted collaboration
                                   between students as they designed their own steps and
      creates opportunities illustrated that more than one way exists to solve a prob-
        for student inquiry lem. I challenged students and let them experience the sci-
                                   entific 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.

54        The Science Teacher
                                                                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 any-
                                                                thing beyond visual observations and prior to disposal (I re-
                                                                quired a disposal check for each lab). If students needed sup-
                                                                plies 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 iden-
                                                                tify several of these 16 substances. To identify the first two,
                                                                aluminum and zinc, density was used. I decided that deter-
                                                                mining density (Lab 2, Figure 1) was a formal lab proce-
                                                                dure students could design on their own (Figure 2, p. 58).
Reviewing the procedures
Before introducing inquiry-based labs, I began by examining     Designing density procedures
many of the current labs scheduled for our sophomore/junior     Because most students already had some familiarity with
chemistry class. Could students be successful doing the lab     density, removing the procedure created a need for them to
without the procedures? Did they have enough background         make connections with prior knowledge (Figure 2). Discussions
information? Would it be safe? I found that many labs could     centered on student recollection of the density formula: Was the
be done successfully without detailed procedures; summary       formula mass divided by volume or volume divided by mass?
descriptions of these labs are provided in Figure 1 (p. 56).    How should the volume of the metal pellets be measured?
   To address safety, students were instructed at the begin-       As students approached the problem, some groups tried
ning of the year on general chemical safety procedures and      putting just the pellets in a graduated cylinder, but quickly
given a safety contract to read and sign. Prior to each lab,    decided that the air between the particles was taking up
special reminders were given regarding specific chemicals;       some of the volume. In the end, to determine the volume
however, because these chemicals and their uses could           most students had success using water displacement in a
change based on students’ ideas, I required that all proce-     range of containers and various amounts of material. The
dures be cleared with me before implementation. This pro-       range of values obtained led to an informative post-lab dis-
cedure review gave me a chance to check for possible safety     cussion on accuracy and precision in measurements.
issues and question student lab design, although I did not         After finding the density, students were asked to identify
usually correct student procedures unless they were unsafe.     their metal from a list of possibilities. I did not show them
   Reviewing lab designs also kept me busy during lab peri-     where to find this information; some students searched the
ods. Instead of providing and correcting procedures, I posed    internet, while others looked in reference books.
questions or problems to solve, and left it up to students to
figure out the experimental steps. To develop procedures         Determining heat of reaction
and conduct experiments, students typically brainstormed        As the year progressed and topics became more novel, I
and worked in groups of four, although occasionally they        had to make sure students received the proper background
worked in pairs and a couple of times as a whole class.         information necessary for successful labs. Occasionally, prior


                                                                                                   October 2005               55
FIGURE 1

Labs without procedures.                                                                         Always wear safety goggles and
                                                                                                 follow proper safety guidelines.

Lab Question/problem posed           Chemicals*                            Background                  Student responses
                                                                           information prior to lab
1    Describe as thoroughly as       Al shot, vinegar, 1 M HCl, corn       General science             Characterized samples by
     possible your unknown           syrup, Zn shot, 1 M NaOH,             experiences. Under-         appearance, solubility in water,
     chemicals.                      CaCO3(s), 0.1 M Na2SO4, 0.1           standing of laboratory      odor, color, viscosity, density,
                                     M BaCl2, CuSO4•5H2O (s),              safety rules.               reaction with each other, etc.
                                     universal indicator, sodium
                                     polyacrylate(s), citric acid(s),
                                     SrCl2 (s), sand and distilled H2O
2    Identify your metal using     Al shot and Zn shot from                Most had some               Most found volume by water
     density (a list of possible   above lab                               experience with density.    displacement and mass on
     choices are given). A                                                                             a balance. Used handbook
     detailed example of this lab                                                                      of chemistry and physics or
     is given in Figure 2 (p. 58).                                                                     chemical dictionary to identify
                                                                                                       metals using the density.
3    Which materials are soluble     (NH4)2SO4, Ca(C2H3O2)2, CaCl2, General knowledge of               Class discussed how much of
     in water and are there any      CoSO4, Cu(C2H3O2)2, MgSO4, KBr, solubility.                       each sample (same mass or
     patterns?                       NaC2H3O2, Na2SO4, NaCl, SrCl2,                                    volume), how much water, and
                                     Ca(NO3)2, KNO3, LiNO3, CaCO3,                                     how long to stir.
                                     BaCO3, MnO2, CuCO3, CuO, ZnO
4    Identify the unknown solution   Unknowns from first lab, 0.1 M         Previous lab examined   Students used precipitation
     from a list of possibilities    Na2SO4 or 0.1 M BaCl2 marked          what chemicals formed   reactions and results from
     (NaCl, Na2SO4, Co(NO3)2,        as letters                            precipitates when mixed.previous lab as a process of
     Pb(NO3)2, K2CrO4, Na3PO4,       [0.1 M of AgNO3, K2SO4,                                       elimination. (Using spot plates
     BaCl2, CuCl2, AgNO3).           Ba(NO3)2, FeCl3, Na3PO4, NaCl]                                and microscale amounts makes
                                                                                                   this more manageable.)
5    What products are formed NaHCO3                                       Students given a brief  Students heated small amounts
     when baking soda is heated?                                           background on baking    of baking soda and weighed
                                                                           soda and three possible material afterwards. Discussions
                                                                           equations.              revolved around how much
                                                                           Students had already    baking soda to use, how long to
                                                                           learned how to          heat it, how it could be heated
                                                                           solve mole-related      safely, and how to perform
                                                                           stoichiometry problems. calculations.
6    Determine how temperature KNO3                                        Previous labs involving Students debated how to keep
     affects the solubility of                                             solubility.             uniform temperature and how
     KNO3.                                                                                         to measure the amount of solid
                                                                                                   that dissolved.


to conducting labs, I would assign related homework to give              when I told them that such an instrument was not available.
students exposure to the knowledge needed. Often, though,                For homework the night before the candle-wax lab, students
I used the lab to introduce new concepts that were then                  had been asked to find the definition of a calorie (students
further developed in class discussions following the lab.                were already familiar with joules). The first successful group
   For example, one lab involved having students determine               decided to place water over the candle and measure the temp-
the amount of heat given off per gram of burning candle wax              erature rise in order to calculate heat. This group was the first
(Lab 8, Figure 1). At first, students wanted to use some type             to make the connection between their homework and the lab.
of meter that would measure heat directly and were puzzled                  Other lab groups developed similar procedures with


56        The Science Teacher
Lab Question/problem posed           Chemicals*                          Background                  Student responses
                                                                         information prior to lab
7     What is the concentration of 0.068 M CuSO4                         Students previously         Students made standards of
      the copper sulfate solution?                                       made and saved              known concentration and
                                                                         solutions of known          compared the colors, others
                                                                         concentrations (0.2 and     evaporated their solution, and
                                                                         0.1 M CuSO4).               one group formed and weighed
                                                                                                     a BaSO4 precipitate.
8     How much energy is          A candle                               The night before this       Students placed water over a
      released per mole of candle                                        lab, students were told     flame and measured increase in
      wax when it burns?                                                 to find the definition        temperature and loss of candle
                                                                         of a calorie. Previously,   mass. Discussions centered on
                                                                         students calculated heats   how much water to use, how
                                                                         of reaction from bond       to place the water above the
                                                                         energies and used joules.   flame, and how to avoid heat
                                                                                                     loss.
9     Determine and graph the         None given                         Students had just done      Students performed a variety of
      quantitative gas relationship                                      exploration involving       tasks. They used balloons, flasks,
      between one of these                                               qualitative observations    thermometer, syringes, and
      pairs—P and V, V and T,                                            of these variables.         pressure gauges.
      or P and T (keeping other
      variables constant).
10    Calculate the heat of solution KNO3, CaCl2, NH4Cl, NaCl            Students familiar with      Students measured mass of solid,
      for four different solids (J/g)                                    heat being absorbed or      placed it in water, and measured
                                                                         released during reactions   temperature change. Different
                                                                         and changes of state.       quantities were used. Too much
                                                                                                     water or too little solid gave
                                                                                                     small temperature changes.
11    Determine and measure two One solution labeled A with 0.02         Students were given a       Students changed temperature,
      factors that will affect the M KIO3 another solution labeled       clock reaction to first      degree of mixing, and
      reaction rate.               B with 4 g starch, 2 g NaHSO3, and    observe before they         concentration of one of the
                                   5 ml of 1 M sulfuric acid per liter   made changes.               reactants.
12    What properties do acids     1 M HCl, 1 M HC2H3O2, 1 M             Previous general            Students remembered acid
      have in common? What do NaOH, 1 M KOH, 6 M HCl, 6 M                knowledge.                  litmus and pH paper tests,
      bases have in common? Do HC2H3O2, 1 M NH4OH, 1 M H3PO4                                         reaction with metals, and
      all acids react the same?                                                                      reaction with baking soda.

* 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.


variations in the amount of water, the position of the water        between two variables (P and T, T and V, or P and V).
above the flame, and the time the candle burned. Postlab                For example, one group examining V and T put a
discussions focused on how to minimize heat “loss” to the           thermometer inside a flask and a balloon on the top of the
environment, and how this affected the accuracy of the lab.         flask. They varied the temperature by placing the flask in
   Gas law labs were my personal favorites of the year (Lab         the refrigerator and then into different hot water baths (the
9, Figure 1). Every group designed distinctly different pro-        balloon was not submerged). At each temperature, volume
cedures. Students worked with ice, balloons, eudiometers,           was measured as the combination of the volume of the flask
syringes, and pressure gauges to discover the relationship          and the volume of the balloon (which students assumed to

                                                                                                         October 2005               57
FIGURE 2                                                                   thoroughly data was recorded. After the student critiques,
Density inquiry lab without procedures                                     I also assessed the notebooks. Students were usually very
                                                                           honest and accurate with their comments.
example. (Taken from Figure 1, Lab 2).                                        In addition to the lab notebook, students wrote lab
Editor’s note: Although various standard density lab procedures            reports that included results, conclusions, and questions. I
are available (see online version of this article at www.nsta.             often graded these myself. For some of the labs, students
org/highschool#journal for an example) students achieve a                  were assessed on accuracy (i.e., did they identify the un-
deeper understanding of the concept of density if they develop             known?). In most cases, however, students demonstrated
a procedure on their own.                                                  understanding through designing successful procedures
                                                                           and analyzing their results thoughtfully.
I. Introduction
   The purpose of this lab is to identify two unknown elements             Obstacles and rewards
   (A and E) from their densities.                                         As expected, the labs were not as efficient without
II. Investigation                                                          procedures. Many labs took more planning time. Labs
    Decide how to determine the density of your materials.                 with defined procedures had been refined over the years to
    You may discuss your plan in groups of four, but each lab              take out all the “kinks.” By removing the procedures, I put
    pair must analyze their own material. Before doing anything,           many of the kinks back in, adding more time to the lab or
    have the teacher OK your procedure for safety. Write your              sometimes creating ambiguous results.
    procedure in your lab notebook.                                           Errors, however, led to great discussions on how to im-
                                                                           prove the labs and insight on creating good lab procedures.
III. Data
                                                                           For example, after discussing student errors with tempera-
     Record your data in your lab notebook in an organized fashion.
                                                                           ture in the rates of reaction lab, students repeated the ex-
IV. Results                                                                periment using their classmates’ suggestions. In hindsight,
    Calculate the density of the material. Show your work in               I wish I had done this for a few more of the labs (e.g., the
    your lab report.                                                       candle wax lab and solubility with temperature). Students
V. Analysis questions                                                      were eager to make improvements and produce more
   Record your responses in your lab report.                               meaningful results; I was surprised by this enthusiasm to
                                                                           repeat a lab. By interpreting ambiguous results and refin-
     a. From the list of possibilities, using reference materials,
                                                                           ing experimental procedures, students achieved a much
        determine the possible identity of your unknown. If possible,      better understanding of the nature of science.
        use other properties (e.g., color, luster) to help identify your      Although there were instances of excitement and ac-
        material. Defend your choice. What additional information          complishment, there were also a few complaints. Some
        would increase your confidence in your identification?               students were initially frustrated when they discovered
     b. Assuming you have correctly identified your material,               that a day’s lab would have no procedure. However,
        what is your percent error? Is your error small enough             when surveyed at the end of the year, student feedback to
        to give you confidence in your identification?                       labs without procedures was positive.
     c. What could have contributed to the error?                             Finally, as I look back over the year, I realize that my
     d. Examine your procedure. List all improvements you would            students did not just simply learn more about chemistry.
        make if you conducted the experiment.                              Despite occasional frustrations, and less efficient methods,
     e. How is density important in everyday life? List as many            students learned how to approach a new problem, brain-
        applications as you can.                                           storm ideas, create a plan of action, perform the tasks, criti-
                                                                           cally analyze the findings, draw conclusions, make adapta-
be close to spherical). Afterward, students graphed results                tions, and start again—and they did it themselves. ■
and even discovered information on absolute zero.
                                                                           Lisa Backus is a science teacher at Deerfield High School, 1959 North
Assessment                                                                 Waukegan Road, Deerfield, IL 60015; e-mail:lbackus@dist113.org.
During all of the experiments in Figure 1, students were
required to keep an accurate account of their analyses in a                         Caution!
lab notebook, including a table of contents, title, purpose,
individual procedures, and data.                                                    It is important to follow standard safety procedures and
   Using this rubric, students swapped notebooks (not with                   appropriate disposal regulations when using chemicals and
their lab partner) and critiqued each others work, then                      lab equipment. This general overview is not intended to cover
critiqued their own. Criteria included the ease with which                   the specific safety precautions for each lab. Consult resources
someone could duplicate the student’s lab based only on the                  such as material safety data sheets, chemical texts, or reference
descriptions in the procedures, and how appropriately and                    books for more detailed information.


58            The Science Teacher

								
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