Observations of Chemical Changes free essay sample

All substances (matter with a definite composition) have characteristics that be used to identify them. These characteristics are referred to as properties. The properties of substances can either chemical or physical. Physical properties are those that do not change the chemical nature of a substance. Dying an Easter egg blue will alter the appearance of the egg not it’s make up. If the nature of a substance were to be altered then the chemical properties have been affected. A good example of a chemical change can be seen repeatedly in our textbook each time a chemical is oxidized. For more examples of physical and chemical substance properties see the map in figure 1. 1. Physical properties are quiet simple to calculate. Determining the solubility or boiling point of a chemical for example is pretty cut and dry. I think this is most likely due to the fact that physical changes do not alter the identity of a substance. Chemical changes, in my opinion, are not as easy to recognize as physical changes. Chemical changes are determined by how a substance reacts with one or more substances when forming compounds. These reactions are known as chemical reactions. (Plaster, Soil Science pg. 13) Not all chemicals will react when mixed with another chemical; while some chemicals can be explosive or toxic when mixed with other chemicals. In previous science courses (soil science and chemistry), and in every day life, I have learned there are â€Å"observable clues† that can be used as indicators of a chemical change. When I drop an Emergent-C tab into a glass of water it reacts by fizzing or bubbling quickly until dissolved. The bubbles are created from gas production. It drives me nuts when a restaurant offers Splenda instead of Sweet-n-Low as a sugar substitute because Splenda doesn’t completely dissolve (insoluble) decaffeinated iced tea. Some Splenda will remain suspended in my glass while some settles in the bottom of my glass. The tea and Splenda formed a compound, but the insoluble Splenda is called a precipitate or a double replacement reaction. (Brown, pg. 47) Ever mixed two clear chemicals together and the compound magically turned a different color. I learned quickly, during a lab about reactions in aqueous solutions last semester that a color change can be a good indicator of a chemical reaction. Prior to beginning my chemistry labs this semester I watched a Lab Paq safety video. The Lab Paq host reminded me that chemicals can react to absorb or give off heat. Temperature changes are classified as exothermic, heat/energy releasing or endothermic, heat/energy absorbing and are both chemical reactions. Figure 1. 1: Properties of Substances (Chang, Raymond, Chemistry, 13th Edition, 2013, McGraw Hill. and www. chemistry. about. com, accecced 9/18/2013) Physical Properties of a Substance Chemical Properties of a Substance Color, smell, and luster Heat of combustion Concentration, fluidity, flow rate Reactivity with water or other chemicals Freezing, melting, and boiling point pH Density, mass, volume Enthalpy of formation Distribution, area Toxicity Electrical conductivity Chemical stability Permeability Flammability Solubility Oxidation states II. Objective Use household products to observe and better understand the chemical properties associated with chemical reactions III. Materials ToothpicksSafety gogglesPaper towels Sheet of white paperWell-Plate-24Pipet, short stem Sheet of dark paperWell-Plate-96Household cleaning supplies IV. Chemicals Ammonia (aq), 1 M – 1 mLBromthymol Blue, 0. 04% 2 mL (in Pipet) Cooper (III) Sulfate, 0. 2 M – 2 mL (in Pipet)FDC Blue Dye #-1, 0. 01% 2 mL (in Pipet) Hydrochloric Acid, 1. 0 M- 1 mLLead (II) Nitrate, 0. 2 M 2 mL (in Pipet) Phenolphthalein Solution 1% 1 mLPotassium Iodine, 0. 1 M – 2 mL (in Pipet) Silver Nitrate, 0. 1 N 2 mL (Dropper Bottle)Sodium Bicarbonate, 1M 2 mL (in Pipet) Sodium Bicarbonate, 1 M – 2 mL (in Pipet)Sodium Hydroxide, 1 M – 1 mL Sodium Hypochlorite, 1% 2 mL (in Pipet)Starch Solution, 1% Stabilized – 2 mL (in Pipet) V. Experiment I will follow each step listed for each of the chemical combinations listed below (under step #4. Titled: Chemical Combinations). A different well of the 96-well plate will be used for each combination. Each chemical combination will be completed 3 times to watch for discrepancies, maintain consistency, and for observations to be made on my beige counter, on white paper, and on black paper. 1. Place 2 pipet drops of the first chemical into one well. 2. Add 2 drops of the second chemical into the same well. 3. Observe: Slide the light and dark sheets of paper (backgrounds) under the well-plate. Record the well-plate number of each mixture next to the coinciding observation 4. Once all combinations have been performed, observations have been recorded, and questions have been reviewed I will clean up. a) Dispose of leftover chemicals by pouring down them sink and flushing with water. b) Rinse the well-plate pipet. Use distilled water for final rinse. Dry the well-plate. d) Wipe down work area with soap and water and wash hands w/ soap water Chemical Combinations Data Table 1: Reactions Expected Well # Chemicals Qualitative Reactions Observed A (1, 2, 3) NaHCO? and HCl CO? No precipitate or color change B (1, 2, 3) HCl and BTB HCl is a strong acid should turn yellow, produces H3O+ ions C (1, 2, 3) NH? and BTB NH3 is basic should turn blue, produces OH- ions D (1, 2, 3) HCl and Blue Dye Not sure, HCl is a strong acid E (1, 2, 3) Blue Dye and NaOCl Not sure, NaOCl (learned about in soil science) it’s used in bleach, can purify water, inexpensive, soluble in water, oxidizing agent F (1, 2, 3) Kl and Pb(NO? )? K (group 1) soluble with I (group 17), Pb Nitrate soluble, K and Nitrates soluble, but Pb and I are an exception; their insolubility will create a precipitate G (1, 2, 3) NaOH and Phenolphthalein NaOH is a base, OH- ions will be produced, solution will turn pinkish- red H(1, 2, 3) HCl and Phenolphthalein HCl is an acid, H3O+ ions are produced, solution will remain clear A (10, 11, 12) NaOH and AgNO? Tried to work a ton of times, but still not sure how these two will react, OH- may precipitate with silver J (10, 11, 12) AgNO? and NH? According to our e-text NH3 is a weak electrolyte, should form NH4+ OH- ions, lab manual suggest patience during this test, causes me to think this reaction is slow, in 2 or more parts, or a reversing reaction K (10, 11, 12) NH? and CuSO? Sulfates ammonium are soluble, Copper will precipitate or be insoluble, H3O+ ions may be produced VI. Observations/Results *The reaction with the best background for observations is highlighted pale yellow Data Table 1: Reactions Observed (on my beige kitchen counter) Well # Chemicals Qualitative Reactions Observed A (1, 2, 3) NaHCO? and HCl CO? Immediate fizzing, Bubbling; translucent Liquid B (1, 2, 3) HCl and BTB Golden yellow at first, then orange color; translucent Liquid C (1, 2, 3) NH? and BTB Royal to deep blue, almost a has a hint of purple, 5 minutes later looked navy blue, translucent Liquid D (1, 2, 3) HCl and Blue Dye Emerald green color, swirls of dark green for first 10-15 sec. ; Opaque liquid E (1, 2, 3) Blue Dye and NaOCl No color change, no bubbles, no precipitate F (1, 2, 3) Kl and Pb(NO? )? Yellow opaque liquid, pale yellow precipitate G (1, 2, 3) NaOH and Phenolphthalein Dark radish red, almost fuchsia in color, no precipitate H(1, 2, 3) HCl and Phenolphthalein White precipitate, hazy liquid A (10, 11, 12) NaOH and AgNO? Fibrous brown baby pooh floating in the bathtub, settles after 3 minutes and brown color fades to grey J (10, 11, 12) AgNO? and NH? Every so slight fizz K (10, 11, 12) NH? and CuSO? Baby to Light Blue in color, cloudy liquid Data Table 2: Reactions Observed (WHITE Background) Well #/Question Chemical Reaction A (1, 2, 3) NaHCO? and HCl CO? Tough to see, but could hear it fizz B (1, 2, 3) HCl and BTB Golden yellow at first, then orange color; translucent Liquid, no precipitate or bubbles C (1, 2, 3) NH? and BTB Turned dark blue with a hint of purple, no precipitate or bubbles D (1, 2, 3) HCl and Blue Dye Swirls of dark emerald green worked through the solution, possible slight precipitate, no bubbles E (1, 2, 3) Blue Dye and NaOCl No visible change in color, no precipitate or bubbles F (1, 2, 3) Kl and Pb(NO? )? Yellow opaque liquid, pale yellow cloudy precipitate, started to settle within 10-15 seconds G (1, 2, 3) NaOH and Phenolphthalein Dark radish red, almost fuchsia in color, no precipitate H(1, 2, 3) HCl and Phenolphthalein Looks like a cup of sprite almost done bubbling or almost out of carbonation, Dark radish red, almost fuchsia in color, white hazy precipitate A (10, 11, 12) NaOH and AgNO? Murky water brown, with fine particles floating around J (10, 11, 12) AgNO? and NH? Hard to see on white paper K (10, 11, 12) NH? and CuSO? Very light to baby blue color change, white cloudy precipitate, no bubbles present Data Table 3: Reactions Observed (BLACK Background) Well #/Question Chemical Reaction A (1, 2, 3) NaHCO? and HCl CO? Layers of various sized bubbles throughout the solution, bubbles and fizzed upon contact with HCl, B (1, 2, 3) HCl and BTB Golden yellow at first, then orange color; translucent Liquid, no precipitate or bubbles, but appeared to lighten in color over time C (1, 2, 3) NH? and BTB Tough to see on black background, almost appeared black in color D (1, 2, 3) HCl and Blue Dye Tough to see on black background, almost appeared black in color E (1, 2, 3) Blue Dye and NaOCl No visible change in color, no precipitate or bubbles F (1, 2, 3) Kl and Pb(NO? )? Yellow precipitate chunks really popped on black, could see cloud forming, looked like a bomb exploding dust and debris up and outwards G (1, 2, 3) NaOH and Phenolphthalein Dark crimson red almost blackish-red with a hint of fuchsia in color, no precipitate H(1, 2, 3) HCl and Phenolphthalein Swirls of small foamy bubbles and a white precipitate forms causing the liquid to be hazy or opaque A (10, 11, 12) NaOH and AgNO? Thick gravy texture, brown sludge eventually settles to the bottom of the well J (10, 11, 12) AgNO? and NH? No color change, has a white precipitate that over time almost completely dissolves K (10, 11, 12) NH? and CuSO? Baby blue color change, white cloudy precipitate, form is easiest to see, clouds seem to dissolve slightly, but blue liquid is murky and opaque VII. Calculations/Errors Before beginning my chemical changes exercise I tried to determine the chemical changes and reaction products. Even though I couldn’t finish all of them it really helped me to know what to look for. Plus, I felt more invested in the lab and more aware of what may be happening chemically to the solutions. Chemical Chemical Equation (to the best of my ability) NaHCO? and HCl CO? NaHCO3 + HCl ? NaCl + CO2 + H2O HCl and BTB H+Cl- + C27H28Br2O5S ? H3O+ + Cl- + (unknown) NH? and BTB NH3 + C27H28Br2O5S ? NH4+ + OH- (unknown) HCl and Blue Dye H+Cl- + C37H34N2Na2O9S3 ? H3O+ + Cl- + (unknown) Blue Dye and NaOCl C37H34N2Na2O9S3 + NaOCl ? + + (unknown) Kl and Pb(NO? )? Pb(NO3)2 + 2KI ? PbI2 + 2KNO3 NaOH and Phenolphthalein NaOH + C2OH14O4 ? NaO2 + CO2 + H2O HCl and Phenolphthalein HCl + C2OH14O4 ? NaOH and AgNO? 2NaOH + 2AgNO3 ? Ag2O + 2NaNO3 + H2OAg2O AgNO? and NH? AgNO3 + NH3 ? NH4+ + OH- + AgO NH? and CuSO? NH? + CuSO? ? NH4+SO4- + Cu + OH- VIII. Discussion/Conclusion During the lab exercise I was given the task of observing chemical changes. I observed double replacement reaction, precipitation reaction, reactions between various chemicals with Bromothymol Blue and Phenolphthalein (acid/base indicators). In the e-text book, Chemistry: The Central Science (Twelfth Edition) , I learned about properties of acids and bases in chapter 4. I was able to use what I learned to aid in understanding what I observed chemically during this exercise. BTB or Bromothymol Blue (acid/base indicators – by color) Acids turned orange with a hint of yellow at the start of the reaction. Bases turned dark blue. Phenolphthalein (acid/base indicator – by color or lack of) Neutral and acidic solutions had no chemical reaction (color change) when combined with the phenolphthalein. Bases on the other hand turned as pink as a radish. Rate of Reaction I’m curious as to way some reactions take so much longer than others. I wonder if it has something to do with how strong of an acid or base it is, or something to do electromagnetic attraction of anions and cations, maybe solubility plays a big role. I’m uncertain what factor or factors determine the rate at which a reaction takes place, but I’d be an interesting topic to look into Knowing the rate of a reaction can aid in maintaining safety or enable one to speed up or slow down a desired reaction. I am now wondering all the possible benefits of knowing the rate of a reaction when it comes to soil and water remediation. Hmmmm†¦ Most importantly, I learned more about physical and chemical changes that could aid in the identification of unknown substances. I was able to practice the scientific method, write and predict chemical equations, get better acquainted with ionic charges (cations and anions), enforce what I learned in chapter 3 about replacement reactions, precipitates and more. I experienced first-hand the indicators that signal a chemical reaction is taking place (e. g. : gas evolution, heat/energy change, color change, and precipitate reaction). IX. Questions A. I could test for the presence of sodium hydrogen carbonate (sodium bicarbonate) in a household product by repeating one of test conducted early in the lab and comparing results. Test: 1. Place 2 pipet drops of the household cleaner into one well. 2. Add 2 drops of HCl (hydrochloric acid) into the same well. 3. Observe, waft smell, record 3. If bubbles are produced then CO2 gas was created and if a Clorox bleach smell is produced then I would assume sodium bicarbonate is present in the cleaner B. Phenolphthalein remains clear when testing an acid or a pH neutral substance and pinkish-red when testing a base. Bromothymol blue turns yellow when testing an acid, green when pH is neutral and blue when testing a base. I tested the household cleaning chemicals below, recorded my observations, and recorded my interpretation of the results. Data Table 2: Reactions Observed Well # Chemical Reaction Interpretation A 12 Windex BTB Dark blue in color, no precip. Windex is basic B 12 Dish Soap BTB Bright yellow color, Dish soap is surprisingly acidic C 12 Lysol Pheno. Light pink color, no precipitate Lysol is basic C. Suppose I found a sample of solution with a faint odor resembling vinegar. I then decided to verify the presence of vinegar by adding a few drops of phenolphthalein. The sample turned pink. I could assume the odor may resemble vinegar, but the sample does not contain vinegar. Vinegar is an acid. In earlier test, only bases turned pinkish-red when mixed with phenolphthalein. D. Using BTB (bromothymol blue), I selected five flavors of the new wave Vitamin Water to test their claimed pH neutrality. Three of the flavor-samples turn a murkey green when combined with BTB, indicating the likelyhood of acid/base (neutral) balance. Of the two remaining samples, one turns slightly yellow when combined with BTB, indicating the pH is most likely 6. 0 or slightly lower and more acidic then the first three samples. The fifth and final sample tested remained blue when combined with BTB, indicating the pH is 7. 6 or higher and is more basic then the first three samples. E. I devised the simple test below to confirm the presence of lead (Pb, an ingredient in Grecian Formula) in a new brand of hair tonic. Test To test the tonic for lead (Pb) I would combined a sample of Pb with potassium iodine (an acid). KI and Pb() react to form a precipitate when combined. If the hair tonic and potassium iodine react to form a bright yellow precipitate I could assume the tonic does indead contain lead. Background Knowledge (Includes: lead, aqueous reactions, precipitate, solubility, replacement reaction) Chemical Equation Pb(NO3)2(aq) + 2KI(aq) PbI2(s) + 2KNO3(aq) Double Replacement Reaction Pb2+(NO3-)2(aq) + 2K+I-(aq) Pb2+I-2(s) + 2K+NO3-(aq) Atoms like to have full valence (outer) electron shells with eight electrons. Depending on how full the valence shell of an element is determines its ability to attract another atom’s electrons. Ions are charged atoms which have lost or gained electrons. Cations are positive charged ions. While negative charged atoms are called anions. Ever heard the saying, â€Å"opposites attract†? Well, the saying is true in chemical reactions. The reaction between lead nitrate and potassium iodine is a double replacement reactions, Meaning the oppositely charged cations and anions â€Å"switch partners†. Net Ionic Equation Pb(NO3)2(aq) + 2KI(aq) PbI2(s) Group one potassium (K), iodine (I), and nitrates (NO3) are soluble in aqueous solutions. Lead (Pb) is soluble with Nitrates (NO3). However, Lead (Pb) is a not soluble with any group 17 elements (F-, Cl-, Br-, I-, and At-). Therefore, two soluble reactants combined to form one insoluble product: a solid bright yellow precipitate. G. During this lab exercise I allowed the chemicals NH3 and CuSO4 to react. The reaction produced a dark blue precipitate known as tetramminecopper(II) sulfate. The ammonia fumes have been known to waft from animal excrement and interact with nearby copper ammunition cartridges, damaginh the casing. Suppose a sample of this metal casing was collected from the site for analysis A researcher recorded the mass of a graduated cylinder filled with 10. 0 mL of water as 14. 1 g. (1mL = 1cm3 = 1g for pure H2O) Volume of H2O: 10. 0 mLMass of Graduated Cylinder: 4. 1 g She placed a chunk of the metal casing into the cylinder and recorded the volume as 11. 4 mL, its mass increased to 16. 6 g. Volume of metal chunk: 1. 4 mLMass of metal chunk: 2. 5 g Density = Mass/Volume or D= m/V in g/cm3 or g/mL D = 2. 5 g/1. 4 mL D = 1. 79 g/mL The density of the metal chunk is 1. 79 g/mL. H. Two pipette drops of each liquid in the table below were allowed to react for one minute. After reviewing the data recorded I can assume the unknown is NH3. I came to this conclusion because the unknown turned pale pink in phenolphthalein an indication it is a base with a pH above 7. 6. The unknown didn’t react with NaHCO3 indicating the substance must be soluble and relatively basic. The student could confirm their choice by testing the unknowns response to CuSO4. If the solution changes to baby blue and a cloudy precipitate forms then the student could assume the unknown is indeed CuSO4. Unknown Phenolphthalein The phenolphthalein turned the unknown pale pink. NaHCO3 No reaction seen Pb(NO3)2 White solid (precipitate formed) AgNO3 Nothing happened I. This lab exercise allowed me to observe several chemical and physical changes. It also improved my ability to recognize the difference between chemical and physical changes. Below I identified and explained some chemical and physical changes.