Chemical Reactions: Introduction to Reaction Types

Transcription

1 Chemical Reactions: Introduction to Reaction Types **Lab Notebook** Record observations for all of the chemical reactions carried out during the lab in your lab book. These observations should include: the appearance of the reactant(s) before the reaction observations of the reaction (the formation of bubbles, flames, color change, precipitation, change in temperature, etc.) Your observations should include color, texture, smell, etc. where applicable. Some of the experiments also require specific chemical tests on reactants and/or products (for example, using litmus paper to test for acidity). Be sure to also record the results of these tests in your lab notebook. The observations should be clearly labeled with the type of reaction and the specific reactants involved, as well as the letters and numbers used in the experiment directions. **You will turn in worksheet pages 6-10 along with the copies of your observations from your lab notebook. Procedure: Safety and waste disposal directions are listed with each procedure. General Directions: 1. Carry out the reactions using the approximate quantities of reagents indicated. Unless otherwise stated, use test tubes. To estimate 2 ml, measure 2 ml of water in a graduated cylinder and pour it into a test tube. Save this test tube for comparison. 2. When combining solutions in a test tube, tap the tube a few times to ensure that the solutions have mixed completely. 3. To heat a solid in a test tube, position the test tube holder near the top of the test tube, and hold the test tube in a slanted position so that the opening of the test tube is pointed away from people. Keep the bottom of the test tube in the hottest part of the burner, but continuously move it back and forth over the flame to avoid hot spots (overheating one part of the test tube). 4. There are two concentrations of HCl(aq) and NaOH(aq) used in this lab: Check labels carefully! A. Acids and Bases CAUTION: NaOH(aq) and HCl(aq) can damage skin, eyes, and clothes on contact. Rinse off any spills immediately with plenty of water for 10 minutes. Neutralize all spills on the lab bench with water or NaHCO 3 solution, and rinse your hands thoroughly. GCC CHM 151LL: Chemical Reactions: Introduction to Reaction Types GCC, 2010 page 1 of 10

2 Place a piece of blue litmus paper and a piece or red litmus paper on a watchglass, leaving a 1-inch gap between them. Place a drop of 0.1M HCl(aq) on both the blue and red litmus paper using a stirring rod, and record your observations. Then, place a drop of 0.1M NaOH(aq) on the blue and red litmus paper, and record your observations. Finally, do the same test with deionized water. If done properly, each piece of litmus paper can be used for multiple tests. Answer these questions in your lab note book: What happens when acids are placed on blue litmus paper? What happens when bases are placed on blue litmus paper? What happens when acids are placed on red litmus paper? What happens when bases are placed on red litmus paper? What happens when deionized water is placed on red and blue litmus? B. Combination Reactions 1. Heat a piece of copper wire strongly in the Bunsen burner flame (using crucible tongs) until a change in appearance is noted. Record any changes in the appearance of the copper wire in your lab report. Place the cooled wire in the regular trash. CAUTION: Do not look directly at the Mg ribbon as it burns, or you may damage your eyes. 2. Hold a strip of magnesium ribbon in the burner flame (using crucible tongs). Record any changes in your lab report. 3. Scrape the ash away from any unreacted Mg metal and place only the ash in a watch glass. Add a few drops of distilled H 2 O to the ashes. Carefully (and thoroughly) crush and stir with a stirring rod. Place a drop of the solution on blue litmus paper on the watch glass, and record your observations. Next, place a drop of the solution on red litmus paper on the watch glass, and record your observations. Refer to section A above to determine if the ashes in the water acidic or basic. Dispose of the wet ash and any unreacted Mg in the waste jar in the hood. Rinse off the pieces of litmus paper with water, then dispose of them in the regular trash. C. Decomposition Reactions 1. Review the demonstration of electrolysis performed by your instructor during the States of Matter lab of the decomposition of water by electrolysis. A current was passed through a sample and decomposed the compound. What tests were performed to determine a chemical change had occurred? 2. Place approximately half a spatula full (roughly pea-sized) of copper(ii) carbonate in a dry test tube. Observe the color of the sample. Using a test tube clamp, heat the test tube over a Bunsen burner until you notice a color change (approximately 30 seconds 1 minute). Be sure to constantly move the test tube to avoid overheating the glassware. Cool the test tube in an empty beaker. Record the color of the solid sample after heating. When cool, dispose of the contents in the waste jar in the hood. GCC CHM 151LL: Chemical Reactions: Introduction to Reaction Types GCC, 2010 page 2 of 10

3 D. Single-Replacement Reactions CAUTION: AgNO 3 will stain skin and clothes! 1. Place a piece of copper wire in a test tube with enough 0.1M AgNO 3 to cover it. Allow the test tube to stand for 5-10 minutes. Note changes in the appearance of both the wire and the solution. Dispose of the contents of the test tube in the waste jar in the hood. CAUTION: 3M HCl(aq) can damage skin and clothing on contact. Rinse any spills on skin immediately with plenty of water for 10 minutes. Neutralize all spills on the lab bench with water or NaHCO 3 solution, and rinse your hands thoroughly. 2. Place a small piece of zinc metal in a test tube containing 2 ml of 3M HCl, and record your observations. Dispose of the contents of the test tube in the waste jar in the hood. E. Double Replacement/Precipitation Reactions Before you begin E, prepare your watch glass for part F by cooling it as described in part F.1 on page 5. **Lab Notebook** In this lab, you will take solutions of: AgNO 3 (aq) NaCl(aq) Ba(NO 3 ) 2 (aq) HNO 3 (aq) Pb(NO 3 ) 2 (aq) And to each you will add solutions of: NaNO 3 (aq) NaCl(aq) Na 2 SO 4 (aq) NaOH(aq) Na 2 CO 3 (aq) KI (aq) What would be the most efficient way to collect your observation data for all of the possible reactions in one single table? What will be the total number of possible reactions? (For a huge hint on how to construct your table, see the example table below.) Number the cells in your table for easy reference to the equations you will be writing. Make sure to leave enough room in your table for short descriptions of what you observe after mixing each pair of solutions. **You will turn in worksheet pages?? (which includes your prelab pages), along with the copies of your observations from your lab notebook. CAUTION: The AgNO 3 (aq) solution stains skin and clothing. Wash any spilled silver ion solution immediately with plenty of water. GCC CHM 151LL: Chemical Reactions: Introduction to Reaction Types GCC, 2010 page 3 of 10

4 CAUTION: NaOH(aq) can easily damage eyes. It is corrosive and can cause chemical burns and damage clothing. Any NaOH(aq) splashed into eyes or spilled on skin must be rinsed immediately with water for 15 minutes. Any NaOH(aq) spilled on your work area must be neutralized, then the entire area should be washed and dried. CAUTION: The nitric acid, HNO 3 (aq), is corrosive, so it can cause chemical burns as well as damage clothing. Any HNO 3 (aq) spilled on skin must be rinsed immediately with water for 15 minutes. Any acid spilled on your work area must be neutralized, then the entire area should be washed and dried. Procedure All observations should be recorded in your data table that you construct in your lab notebook. If no change is observed, record NR for no reaction. An example for a different set of ions (not ones you will use in this lab) is shown in the Example Table below. Example Table: Observations of Experimental Results KNO 3 (aq) KI(aq) KOH(aq) CuCl 2 (aq) NR cloudy brown ppt cloudy blue ppt Pb(NO 3 ) 2 (aq) NR cloudy yellow ppt cloudy white ppt KCl(aq) NR NR NR Part A: Mixing Known Solutions NOTE: All waste for this experiment should go into the labeled waste containers in the hood. Do not dispose of any solutions or solids down the drain. 1. Wash your well-plate thoroughly using soap and water, then rinse it with deionized water and dry completely to prevent any errors from contamination. A dirty and contaminated well-plate can give incorrect results. 2. Place 5 drops of the aqueous solutions in the correct well plates based on the table you constructed (for example, in the first well, you will add 5 drops of AgNO 3 (aq) and NaNO 3 (aq)). 3. Use blue and red litmus paper to determine if the following chemicals are acids, bases, or neither (record your results in your lab notebook): NaCl (aq) HNO 3 (aq) Na 2 CO 3 (aq) 4. Because of the small amounts used, some reactions may be hard to observe on the small well plates. Therefore, test the following reactions on a larger scale by placing 10 drops of each in a separate clean test tube: Ba(NO 3 ) 2 (aq) and NaOH (aq) HNO 3 (aq) and NaOH (aq) HNO 3 (aq) and Na 2 CO 3 (aq) GCC CHM 151LL: Chemical Reactions: Introduction to Reaction Types GCC, 2010 page 4 of 10

5 5. Have your lab instructor sign off on your results. List all combinations of solutions where reactions occur, along with the products formed, in your lab notebook. Note: The reaction between HNO 3 (aq) and Na 2 CO 3 (aq) initially forms carbonic acid, H 2 CO 3 (aq), which then immediately decomposes into H 2 O (l) and CO 2 (g) F. Combustion Reactions 1. Place your watch glass in the Styrofoam cooler in the hood. Make sure the watch glass does not come into contact with water or this will interfere with the reaction in part 2. It can be placed on top of the metal grating in the Styrofoam cooler. This setup will cool your watch glass to facilitate observations in part 2 (below). The watch glass should cool for about 10 minutes before you begin part Place about drops of isopropyl alcohol (C 3 H 7 OH) in a small evaporating dish (on a wire gauze and ring clamp see the figure below). Using a second ring clamp about 8 10 inches above the evaporating dish, place a cold watch glass (chilled in the Styrofoam cooler) on the upper ring stand. Also place a few pieces of ice on the watch glass. Ignite a wooden splint in the Bunsen burner and use the burning wooden splint to light the alcohol. Note the condensation of water on the bottom of the watch glass. You may have to repeat this procedure a few times to see the condensation. If you keep the watch glass above the flame too long or if the flames reach too high and touch the watch glass, the condensed water will evaporate! GCC CHM 151LL: Chemical Reactions: Introduction to Reaction Types GCC, 2010 page 5 of 10

6 Chemical Reactions: Introduction to Reaction Types: Lab Report Name: Partner(s): Section Number: Video Reactions: Record your observations of the video reactions chosen by your instructor. Your instructor will discuss the reactions with you. 1. Combination: 2. Decomposition: 3. Single Replacement: 4. Double Replacement/Precipitation: 5. Acid-Base Neutralization 6. Combustion: GCC CHM 151LL: Chemical Reactions: Introduction to Reaction Types GCC, 2010 page 6 of 10

7 Post-Lab Questions Word Equations and Balanced Chemical Equations Translate each of the following word equations into a balanced chemical reaction by writing the correct chemical formulas (including physical states) for the reactants and products. Make sure to balance each equation. Example: Aluminum metal reacts with oxygen to form solid aluminum oxide. aluminum metal + oxygen gas aluminum oxide 4 Al (s) + 3 O 2 (g) 2 Al 2 O 3 (s) A. Combination Reactions 1. Copper reacts with oxygen to form copper(ii) oxide. copper metal + oxygen gas copper(ii) oxide 2. Magnesium metal reacts with oxygen to form magnesium oxide. magnesium metal + oxygen gas magnesium oxide 3. Magnesium oxide (ash) reacts with water to form magnesium hydroxide. magnesium oxide + water magnesium hydroxide B. Decomposition Reactions 1. Water decomposes into hydrogen gas and oxygen gas. water hydrogen gas + oxygen gas 2. Copper(II) carbonate decomposes into copper(ii) oxide and carbon dioxide gas. copper(ii) carbonate copper(ii) oxide + carbon dioxide gas GCC CHM 151LL: Chemical Reactions: Introduction to Reaction Types GCC, 2010 page 7 of 10

8 C. Single-Replacement Reactions 1. Copper reacts with silver nitrate to form silver metal and copper(ii) nitrate. copper metal + silver nitrate silver metal + copper(ii) nitrate 2. Zinc metal reacts with hydrochloric acid to produce zinc chloride and hydrogen. zinc metal + hydrochloric acid zinc chloride + hydrogen gas D. Dobule Replacement (precipitation) and Acid Base Reactions Refer to your data table for the following selected sets of reactants and fill in the following blanks and beaker drawings. If there is no net ionic reaction because all the ions are spectators still complete the molecular reaction, the ionic reaction, and the beaker drawings, then put NR for the net ionic reaction. An example NOT from this experiment is presented first. Example: calcium acetate and ammonium sulfate Reaction type: precipitation Molecular: Ca(CH 3 COO) 2 (aq) + (NH 4 ) 2 SO 4 (aq) CaSO 4 (s) + 2 NH 4 CH 3 COO(aq) Ionic: Ca 2+ (aq) + 2 CH 3 COO - (aq) + 2 NH 4 + (aq) + SO 4 2- (aq) CaSO 4 (s) + 2 CH 3 COO - (aq) + 2 NH 4 + (aq) Net Ionic: Ca 2+ (aq) + SO 4 2- (aq) CaSO 4 (s) + 1. lead (II) nitrate and potassium iodide Reaction type: Molecular: Ionic: Net Ionic: + GCC CHM 151LL: Chemical Reactions: Introduction to Reaction Types GCC, 2010 page 8 of 10

9 2. nitric acid and sodium hydroxide Reaction type: Molecular: Ionic: Net Ionic: + 3. barium nitrate and sodium sulfate Reaction type: Molecular: Ionic: Net Ionic: + 4. silver nitrate and sodium chloride Reaction type: Molecular: Ionic: Net Ionic: + F. Combustion Reactions GCC CHM 151LL: Chemical Reactions: Introduction to Reaction Types GCC, 2010 page 9 of 10

10 1. Isopropyl alcohol burns in air to produce carbon dioxide and steam. isopropyl alcohol, C 3 H 7 OH (l) + oxygen gas carbon dioxide gas + steam Balancing and Categorizing Chemical Equations: Balance each of the 12 chemical equations given below, and identify each as one of the six types listed below. Combination reaction (C) Decomposition reaction (D) Single-Replacement reaction (SR) Double-Replacement/Precipitation reaction (DR) Acid-Base Neutralization reaction (N) Combustion reaction (B) TYPE 1. Al (s) + NiCl 2 (aq) Ni (s) + AlCl 3 (aq) Ba(OH) 2 (s) + FeCl 3 (aq) BaCl 2 (aq) + Fe(OH) 3 (s) C 4 H 10 (l) + O 2 (g) CO 2 (g) + H 2 O (g) 4. KClO 3 (l) KCl (l) + O 2 (g) 5. Al (s) + I 2 (s) AlI 3 (s) 6. H 2 SO 4 (aq) + Mg(OH) 2 (s) H 2 O (l) + MgSO 4 (aq) 7. CH 3 OH (l) + O 2 (g) CO 2 (g) + H 2 O (g) 8. Ca (s) + O 2 (g) CaO (s) 9. Mg (s) + CO 2 (g) MgO (s) + C (s) 10. Na 3 PO 4 (aq) + MgCl 2 (aq) Mg 3 (PO 4 ) 2 (s) + NaCl (aq) 11. HgO (s) Hg (l) + O 2 (g) 12. H 3 PO 4 (aq) + NaOH (aq) H 2 O (l) + Na 3 PO 4 (aq) GCC CHM 151LL: Chemical Reactions: Introduction to Reaction Types GCC, 2010 page 10 of 10