Teacher Notes

Iron Corrosion

Guided-Inquiry Kit

Materials Included In Kit

Agar, 20 g
Iron nails, 2–3" long, 40
Aluminum (Al) (6–12 inch piece, cut down to 5–7 cm in length)
Ammonium chloride solution, NH4Cl, 0.5 M, 200 mL
Copper (Cu) (6–12 inch piece, cut down to 5–7 cm in length)
Hydrochloric acid solution, HCl, 0.1 M, 200 mL
Phenolphthalein indicator solution, 1%, 50 mL
Lead (Pb) (6–12 inch piece, cut down to 5–7 cm in length)
Magnesium (Mg) (6–12 inch piece, cut down to 5–7 cm in length)
Potassium ferricyanide solution, K3Fe(CN)6, 0.1 M, 50 mL
Sodium bicarbonate solution, NaHCO3, 0.5 M, 200 mL
Sodium chloride solution, NaCl, 0.5 M, 200 mL
Sodium oxalate, Na2C2O4, 10 g
Tin (Sn) (6–12 inch piece, cut down to 5–7 cm in length)
Zinc (Zn)
Petri dishes with covers, disposable plastic, 20
Sandpaper sheet, 9" x 11"
Weighing dishes, 10

Additional Materials Required

Water, distilled or deionized
Beaker, 400-mL
Hot plates or Bunsen burners, 3–5
Labels and marking pen
Pliers, 2 pair
Scissors, heavy-duty, or wire clippers
Spatula
Stirring rod
Weighing dish Surface Coating Materials Chemically treated: Rust-Oleum® paint
Oil-based: WD-40®
Solid linings: Duct tape, transparent tape
Water-resistant: Candle wax, nail polish (clear), permanent marker (Sharpie®), petroleum jelly, silicone grease
Water-soluble: Glue, latex paint, hand lotion

Prelab Preparation

Sodium oxalate solution, saturated: Add 10 g of sodium oxalate to 200 mL of distilled water. Stir to dissolve. Some undissolved sodium oxalate should remain at the bottom after mixing.

*Prepare a 1% suspension of agar in boiling water. Dissolve 1.5 g of agar along with 1 mL each of the two indicators in 150 mL of boiling water to give enough agar for two corrosion tests (Petri dishes).

Safety Precautions

Potassium ferricyanide solution is a skin and eye irritant. Contact with concentrated acids may generate toxic hydrogen cyanide gas; avoid contact with strong acids. Phenolphthalein is an alcohol-based solution—it is a flammable liquid and moderately toxic by ingestion. Keep away from flames and other sources of ignition. Avoid contact of all chemicals with eyes and skin. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Please review current Safety Data Sheets for additional safety, handling and disposal information. Remind students to wash their hands thoroughly with soap and water before leaving the lab.

Disposal

Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures, and review all federal, state and local regulations that may apply, before proceeding. The Petri dishes and their contents may be discarded in the trash (solid waste) according to Flinn Suggested Disposal Method #26a.

Lab Hints

A good way to begin this activity is with a class discussion of what students already know about rusting and how it can be prevented. Many students will have prior knowledge of methods of corrosion protection (galvanized iron, rust removers, Rust–Oleum® paint, anodized aluminum, etc.).|For best results, schedule at least two 50-minute periods for completion of this activity. Students will need one day to observe the standard test method demonstration (see the Pre-Lab Activity) and plan their investigation (see the Procedure), and a second day to prepare the nails and gels for the corrosion test. Students and teachers should agree in advance on a uniform duration for the corrosion test—24 hours (1 day) appears to be optimum. Although indicator color changes are usually apparent after 20–30 minutes, rust formation typically takes about 24 hours to develop. Some metal treatments that appear to prevent corrosion in the short term may not be effective after longer periods of time. After 72 hours the indicator color changes and rust formation will likely be extensive, making it more difficult to interpret the results. The plates also become perfect incubators for mold after 3–5 days.|See the Standard Test Method (page 7) for a step-by-step procedure of the standard test method.|If you have never prepared agar before, consult with your biology teacher colleagues for advice. You may want to prepare a small batch for practice before doing the Pre-Lab Activity. The water must be heated to get the agar to dissolve, but if it gets too hot, the agar will burn. Many biology teachers use a microwave oven to heat the agar mixture. Use a dedicated lab microwave only.|The metals are easy to distinguish. Aluminum and copper are wires, the magnesium is a strip, and the zinc is a foil. The tin and lead strips can be distinguished by feel. The lead is very malleable and soft compared to the tin strip.|Student preparation is an essential element for success in a student-directed inquiry activity. To ensure a safe lab environment, however, it is also critical that the teacher review each group’s materials list and their procedure, including any necessary safety precautions, before allowing students to work in the lab.|Notice that no specific suggestions regarding metal treatment have been given in the student section for this activity. This is intentional—students are generally more motivated if they feel they “own” the experiment. Students may bring many possible coating materials from home for testing in the lab. The teacher may want to schedule additional prep time for students who wish to test chemical additives in the gels or different metal combinations. A compromise arrangement is for the teacher to give the students in advance a master list of materials that are available in the lab for testing. See the Materials and the Sample Data sections for suggestions.|To test the effect of different chemical additives, 1% agar gels may be prepared using dilute solutions of acids, bases, salts, oxidizing agents, reducing agents, etc., rather than water. Heat 100 mL of the desired solution to boiling on a hot plate, add 1 g of agar, and stir continuously until the agar forms a uniform suspension. Remove the agar from the hot plate, add the indicators, and allow the agar to cool (but not harden) before pouring the plates and adding the nails.|Some chemical additives will interfere with the use of the indicators. Any basic solution will give a pink gel with phenolphthalein. In the absence of phenolphthalein indicator, however, the potassium ferricyanide indicator can still be used to detect the formation of Fe2+ ions. (Testing basic additives gives interesting results—see the Sample Data section. Sodium bicarbonate completely inhibits the corrosion process.) If an acidic solution is used to prepare the gel, any hydroxide ions generated during the corrosion process will neutralize the acid and will not cause an indicator color change with phenolphthalein. Students may ask about other acid–base indicators that might work with acid or base additives. “Rainbow acid universal indicator” available from Flinn Scientific (Catalog No. U0012) may give detectable color changes in an acidic gel if hydroxide ions are generated. See the table of indicators and their pH ranges in the Chemicals section of your current Flinn Scientific Catalog/Reference Manual for a complete listing of acid–base indicators. Let students try different indicators.|Alternative indicators that may be used to used to detect iron ions include phenanthroline (for Fe2+ ions) and potassium thiocyanate (for Fe3+ ions). Phenanthroline (0.1% solution, Catalog No. P0215) gives a positive test (peach color) in regions of the gel where iron is oxidized. Thiocyanate gives a negative test result in the initial stages of the corrosion process but does show a faint positive test (orange color) after 2–3 days when the nail has become rust-covered.|Sanding the nails (see the Standard Test Method) may affect the corrosion process, in particular, where oxidation originates. This is an additional variable that students may choose to study. We recommend using sandpaper rather than steel wool to sand the nails. If steel wool is used, the nails must be thoroughly wiped clean to remove tiny particles of steel wool from the nails.|Use “bright common” (all-purpose) nails for this experiment. Do not use galvanized nails!

Teacher Tips

  • The concept of a “fair test” is used in the Procedure section to get students to think about the design of their experiment. Students may hypothesize, for example, that a water-resistant (impermeable) coating will prevent corrosion. Is it fair to test only water-resistant coatings? Students must identify the condition they wish to manipulate (the independent variable) and the response they wish to observe or measure (the dependent variable). A “fair test” experiment is one in which all other experimental conditions are kept the same (the controlled variables).
  • Communication of results and analysis of alternative explanations or models are integral parts of the National Science Education Standards for inquiry-based instruction. This activity offers a perfect opportunity for students to practice these skills. To help students achieve the inquiry standards, promote a cooperative approach in the classroom. Use the classroom discussion prior to lab to encourage the class as a whole to investigate a variety of treatment approaches. During the post-lab discussion, students should communicate their results to the class either in writing or verbally. The class may then review all the findings and weigh the evidence and logic for alternative interpretations or explanations of the results.

Correlation to Next Generation Science Standards (NGSS)

Science & Engineering Practices

Asking questions and defining problems
Developing and using models
Planning and carrying out investigations
Analyzing and interpreting data
Constructing explanations and designing solutions
Obtaining, evaluation, and communicating information
Engaging in argument from evidence

Disciplinary Core Ideas

MS-PS1.B: Chemical Reactions
HS-PS1.B: Chemical Reactions
HS-ETS1.A: Defining and Delimiting Engineering Problems

Crosscutting Concepts

Patterns
Cause and effect
Systems and system models
Energy and matter
Structure and function
Stability and change

Performance Expectations

MS-PS3-1: Construct and interpret graphical displays of data to describe the relationships of kinetic energy to the mass of an object and to the speed of an object.
MS-PS3-2: Develop a model to describe that when the arrangement of objects interacting at a distance changes, different amounts of potential energy are stored in the system.
HS-PS2-2: Use mathematical representations to support the claim that the total momentum of a system of objects is conserved when there is no net force on the system.
HS-PS3-1: Create a computational model to calculate the change in the energy of one component in a system when the change in energy of the other component(s) and energy flows in and out of the system are known.

Answers to Prelab Questions

Standard Test Method (Pre-Lab Activity) The following procedure describes the preparation of the agar gel for the pre-lab demonstration. The demonstration is used to illustrate the “standard” test method and to visualize the evidence for the electrochemical model of iron corrosion. A similar procedure may be used to test a variety of metal treatment options. 1. Clean two iron nails with sandpaper or steel wool. Bend one of the nails at a 90° angle using two pairs of pliers. 2. Obtain 75 mL of distilled or deionized water in a 250-mL beaker and heat the water to boiling on a hot plate. Hint: Our biology teacher friends report that they like to use a microwave oven. 3. Add 0.75 g of powdered agar to the boiling water. Stir continuously until the agar forms a uniform suspension. Be careful not to burn the agar. 4. Carefully remove the beaker from the hot plate and add 5 drops of 1% phenolphthalein solution and 10 drops of 0.1 M potassium ferricyanide solution. Stir to mix. (The suspension will be yellow in color.) 5. Allow the agar to cool but not harden. 6. Place the two cleaned nails (step 1) in the bottom of a disposable plastic Petri dish. Make sure the nails are not touching. 7. Pour the agar suspension into the Petri dish so that the nails are completely submerged and covered with agar. 8. Cover the Petri dish and set it aside for later viewing—24 hours is optimum, although indicator color changes may be apparent after about 30 minutes. Answers to Pre-Lab Activity (Student answers will vary.) 1. Observe the nails and the indicator colors in the standard corrosion test. Record all observations in the diagram below. {12626_Answers_Figure_2} 2. Which parts of the straight nail (the control) oxidized most readily? What evidence supports this? Suggest a possible reason for the observation. Oxidation of iron appeared to originate at two sites—the head and the tip of the nail. The evidence for this is the location of blue areas in the gel where Fe2+ ions were produced. Oxidation originates at points on the nail that have been “stressed” in the manufacturing process. Note to teachers: Metalworking causes dislocation of iron atoms and creates defects in the crystal structure. 3. Compare the results obtained for the bent nail versus the control. Did bending the nail change where oxidation of the metal was most likely to start or the amount of rust that was observed? Explain. Bending the nail changed the location at which oxidation originated. The blue color due to reaction of Fe2+ ions with ferricyanide indicator began at the 90° bend in the nail and proceeded in either direction away from the bend. The head and the tip of the nail were surrounded by pink areas in the gel, indicating the presence of OH– ions. Both nails were covered with rust after 24 hours. 4. According to the electrochemical model for iron corrosion, the corrosion process takes place via two separate half-reactions. Electrons flow through the metal, like electricity through a wire, from the site where iron is oxidized to the site where oxygen is reduced. Do the indicator color changes support this model for iron corrosion? The indicator color changes suggest that oxidation and reduction occur at different sites on the nail—there are distinct and separate blue and pink regions in the gel. The blue areas indicate the presence of Fe2+ ions due to oxidation of iron atoms. The pink regions indicate the presence of OH– ions due to reduction of oxygen in the presence of water. Note to teachers: Evidence from other experiments also supports the electrochemical model of corrosion. First of all, the reaction requires water (about 40% relative humidity is required). Water is required for migration of ions and to neutralize charge buildup in an electrochemical reaction. Secondly, two distinct types of corrosion damage are generally observed—pitting or cracking in the metal structure where iron atoms have been lost, and the buildup of rust deposits. The two types of corrosion damage occur at different locations on the metal surface. This suggests a two-fold process. Oxidation results in the release of electrons and gives rise to pits and cracks in the iron surface where the iron has dissolved. The electrons flow through the metal, as they might through a wire that conducts electricity, until they react with oxygen and water to produce hydroxide ions. In the presence of water or moisture on the metal surface, the Fe2+ ions migrate until they reach the region where OH– ions have been produced. There they combine with OH– ions or react further with oxygen to form rust. The formation of rust at sites far removed from where the iron has dissolved is compelling evidence for the electrochemical nature of the rusting process.

Sample Data

A. Chemical Additives—Sodium bicarbonate (a basic salt), sodium chloride (a neutral salt), and sodium oxalate (a basic salt and strong reducing agent) were tested. 1% agar suspensions were prepared using 0.5 M solutions in place of deionized water. Phenolphthalein and potassium ferricyanide were added to the agar before pouring the plates. (Phenolphthalein was not added to the sodium bicarbonate gel.) Compared sanded (left side) versus unsanded (right side) nail in each gel. Results should be compared against the control (sanded) nail in the pre-lab demonstration. {12626_Data_Figure_3} B. Surface Coatings—Water-soluble versus water-resistant, chemically treated, and oil-based coatings were investigated, along with solid linings. All nails were sanded before testing. Gels were prepared using 1% agar in deionized water. Phenolphthalein and potassium ferricyanide were added to the agar before pouring the plates. Results should be compared with the control nail in the pre-lab demonstration. Water-soluble: Glue, latex paint, hand lotion Water-resistant: Candle wax, nail polish (clear), permanent marker (Sharpie®), petroleum jelly, silicone grease Chemically treated: Rust-Oleum® paint Oil-based: WD-40® Solid linings: Duct tape, transparent tape {12626_Data_Figure_4}  {12626_Data_Figure_5} C. Combinations of Metals — More and less active metals (compared to iron) were tested in 1% agar gels prepared with deionized water. All nails and all metals were sanded before use. Wires or metal strips were wrapped around the nails. Phenolphthalein and potassium ferricyanide were added to the agar before pouring the plates. Results should be compared against the control nail in the pre-lab demonstration. More active metals: Aluminum, magnesium, zinc Less active metals: Copper, lead, tin Additional variables to consider: (1) Does the second metal have to be attached to the nail? How is the metal attached to the nail? Does it have to cover the nail, span the length of the nail, or just make contact with the nail? (2) Does it matter if the second metal has been polished (sanded) before testing? {12626_Data_Figure_6} Sample Results and Conclusions Chemical Additives A neutral salt (NaCl) environment accelerated the corrosion of iron. A basic salt (NaHCO3) or a reducing salt (Na2C2O4) environment prevented the corrosion of iron. Possible Explanations: Electrolytes increase the rate of an electrochemical reaction. High concentrations of OH– ions—a product of corrosion—shift the position of equilibrium for reduction of oxygen to hydroxide ions. A reducing agent provides an alternative source of electrons for the reduction of oxygen. (The reducing agent competes with iron as the site of oxidation.) Opportunities for further testing: Acidic salts, oxidizing salts, non-ionic bases (such as ammonia), and neutral reducing agents (such as hydroquinone, ascorbic acid). Surface Coatings Water-resistant coatings (wax, grease, nail polish) inhibited the corrosion process—neither oxidation nor reduction products were observed in the gel. The nail must be completely covered for corrosion protection to be effective. Any breaks, no matter how small, in the coating acted as sites for iron oxidation. Water-resistant coatings that adhered to the metal surface (transparent tape, wax, and nail polish) appeared to be most effective. Petroleum jelly appeared to inhibit the corrosion process for a short time (1–2 hours), but did not provide long-term corrosion protection. It’s possible that the coating eroded due to mixing or diffusion into the surroundings. Painting a nail with water-permeable latex paint also protected the nail against corrosion. Again, however, any break in the coating where the nail was not covered provided a site where the redox reaction was initiated. Latex paint, even when dry, is water-permeable. This suggests that the ability of the coating to adhere to the nail may be a crucial variable. Elmer’s® glue, a water-based coating that adheres to the metal, seemed to increase the amount of corrosion that was observed. This is probably not a good “fair test” subject, however, because glue contains many chemical additives. Lotion is also water-based and does not adhere to the metal—it did not offer any corrosion protection and may have accelerated corrosion. Lotion also contains many chemical additives. Possible Explanations: Water is necessary for corrosion to occur. “Simple” hydrocarbon-based, water-resistant coatings, such as wax or silicone grease, provide effective, long-term corrosion protection by preventing contact of the nail with water. The rigidity of the coating is a co-variable but is not a necessary condition. The ability of the coating to adhere to the metal is another co-variable. For water-permeable coatings, it is difficult to isolate the critical variable—is it the rigidity of the coating, its ability to adhere to the metal, or its chemical composition? The presence of a variety of chemical additives makes it hard to design a “fair test” experiment for this type of metal treatment. Combinations of Metals and Metal Activity Combining a nail with a metal that is more active than iron (magnesium, aluminum, and zinc) protected iron against corrosion— no rust was observed and there were few or no blue regions in the gel. Pink sites in the gel verified that reduction of oxygen was still taking place when these more active metals were present. Zinc was the most effective “second metal” in reducing the corrosion of iron. Magnesium gave unreliable results—sometimes it prevented corrosion entirely (as it should), while other times it prevented corrosion only where it was attached to the nail. Metals that are less active than iron (copper, lead, and tin) did not protect iron against corrosion. The standard test method used in this experiment was a qualitative test. It is not possible to conclude whether the less active metals actually accelerated the corrosion of iron. Note to teachers: The more active metal does not have to be wrapped around the nail to offer corrosion protection—it only needs to make “electrical contact” with the iron in one location. More active metals protect iron against corrosion even if the less active metal is not sanded or polished before use. Aluminum is known to form a tough, durable coating that retards the reaction of aluminum with water or acids. It is interesting that the surface oxide coating does not interfere with the ability of aluminum to protect iron against corrosion. Possible explanations: The results support the electrochemical model for iron corrosion. The activity series of the metals lists the metals in order of reactivity. Reactivity can be defined as the ease of oxidation. Metals at the top of the activity series are said to be more active—they are more reactive and more easily oxidized. When two metals are present together and both are exposed to oxygen and water, competition between the two results in the more reactive (more easily oxidized) metal reacting preferentially with oxygen. The more reactive metal protects the less reactive metal from the oxidizing effects of oxygen. The activity series for metals that could be tested in this experiment is summarized below: Mg > Al > Mn > Zn > Cr > Fe > Co > Ni > Sn > Pb > Cu > Ag > Au

References

This experiment has been adapted from Flinn ChemTopic™ Labs, Volume 16, Oxidation and Reduction; Cesa, I., Ed., Flinn Scientific: Batavia, IL, 2004.

Student Pages

Iron Corrosion

Introduction

Corrosion is defined as the chemical or electrochemical degradation of metals due to their reaction with the environment. The corrosion of iron, better known as rusting, is an oxidation–reduction process that destroys iron objects left out in open, moist air. In the United States alone, it is estimated that the cost of corrosion—in equipment maintenance, repair and replacement—exceeds $300 billion per year. What kinds of chemical treatments, surface coatings or combinations of metals will prevent the corrosion of iron?

Concepts

  • Corrosion
  • Oxidation–reduction
  • Half-reactions
  • Activity of metals

Background

When iron metal is exposed to oxygen and water, a familiar result is observed—rust. The rusting process consists of several steps. In the first step, iron is oxidized to iron(II) ions, Fe2+, and oxygen from the air is reduced to hydroxide ions, OH. This oxidation–reduction reaction takes place via two separate half-reactions (Equations 1 and 2).

{12626_Background_Equation_1}
{12626_Background_Equation_2}
Combining the oxidation and reduction half-reactions so the electrons “cancel out” gives the balanced chemical equation for the overall reaction of iron, oxygen, and water (Equation 3). Notice that two iron atoms are oxidized for every oxygen molecule that is reduced—the number of electrons gained by one oxygen molecule is equal to the number of electrons given up by two iron atoms.
{12626_Background_Equation_3}
Fe2+ and OH ions may combine to form solid iron(II) hydroxide, Fe(OH)2 (Equation 4). This is almost never observed, however, because iron(II) hydroxide reacts further with oxygen and water to form hydrated iron(III) oxide, Fe2O3nH2O, the flaky, reddish-brown solid commonly known as rust (Equation 5).
{12626_Background_Equation_4}
{12626_Background_Equation_5}

Experiment Overview

The purpose of this activity is to investigate chemical additives, surface coatings, and combinations of metals that will reduce or prevent the corrosion of iron. Each group of students will be responsible for developing a hypothesis and designing a “fair test” to determine how and why different conditions affect the corrosion of iron. In order to compare results obtained by different student groups, the corrosion of iron will be studied using a standard test method.

Materials

Agar, 1.5 g*
Water, distilled or deionized, 150 mL*
Iron nails, 4
Phenolphthalein indicator solution, 1% in alcohol, 1 mL
Potassium ferricyanide solution K3Fe(CN)6, 0.1 M, 1 mL
Beaker, 400-mL
Hot plate or Bunsen burner
Chemical additives or test solutions (extra needed for working hypotheses)
Metal wires, strips or ribbons (extra needed for working hypotheses)
Labels and/or marker pen
Petri dishes with covers, disposable plastic, 2
Pliers
Sandpaper or steel wool
Spatula
Stirring rod
Surface coatings or linings (extra needed for working hypotheses)
Weighing dish
*See Prelab Preparation.

Prelab Questions

The following demonstration illustrates the standard test method that will be used in this experiment and provides evidence for the electrochemical nature of corrosion. Two iron nails were cleaned and sanded, and one of the nails was bent to a 90° angle. The nails were placed in a Petri dish and covered with warm agar containing two indicators. Upon cooling, the agar formed a stable, semi-solid gel. Phenolphthalein, an acid–base indicator, was added to detect the formation or presence of hydroxide ions. Phenolphthalein is colorless in acidic or neutral solutions but turns bright pink in basic solutions (pH > 8–10) due to reaction with OH– ions. Potassium ferricyanide, K3Fe(CN)6, was added to detect the formation or presence of iron(II) ions. Ferricyanide ions react with Fe2+ ions to form a dark blue mixed iron(II)/iron(III) compound, Fe3[Fe(CN)6]2, commonly known as Prussian blue (Equation 6). {12626_PreLab_Equation_6} 1. Observe the nails and the indicator colors in the standard corrosion test. Record all observations in the diagram below. {12626_PreLab_Figure_1} 2. Which parts of the straight nail (the control) oxidized most readily? What evidence supports this? Suggest a possible reason for the observation. 3. Compare the results obtained for the bent nail versus the control. Did bending the nail change where oxidation of the metal was most likely to start or the amount of rust that was observed? Explain. 4. According to the electrochemical model for iron corrosion, the corrosion process takes place via two separate half-reactions. Electrons flow through the metal, like electricity through a wire, from the site where iron is oxidized to the site where oxygen is reduced. Do the indicator color changes support this model for iron corrosion? Explain.

Safety Precautions

Potassium ferricyanide solution is a skin and eye irritant. Contact with concentrated acids may generate a toxic gas; avoid contact with strong acids. Phenolphthalein is an alcohol-based solution—it is a flammable liquid and moderately toxic by ingestion. Keep away from flames and other sources of ignition. Avoid contact of all chemicals with eyes and skin. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Wash hands thoroughly with soap and water before leaving the lab.

Procedure

Study the mechanism of the corrosion process (see the Background section) and the evidence for this mechanism (see the Pre-Lab Activity). 1. Form a working group with two other students and brainstorm the following questions. • What chemical additives might reduce or prevent the corrosion of iron? • What type of surface coatings might inhibit the corrosion of iron? • What combinations of metals might prevent the corrosion of iron? • What other types of metal treatment might reduce the corrosion of iron? 2. Choose one general type of metal treatment and develop an “if/then” hypothesis to describe its effect: If a nail is combined or treated with ________________ , then the amount of corrosion should ________________, because _________________________. Write the hypothesis on the worksheet. 3. Design a “fair test” experiment to test the hypothesis—choose at least 3–4 specific examples of metal treatment that may provide evidence both for and against your hypothesis. What other variables might affect the test? How can these variables be controlled? 4. Write a detailed, step-by-step procedure for your experiment and verify the procedure and the required safety precautions with your instructor. Carry out the experiment and record observations on the worksheet.

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