PLEASE – do NOT write on this paper. RETURN this paper at the end of the class period. THANKS Learning Activity 4cd: Lab – Ionic and Covalent Compounds Unit E: Matter and its Interactions Learning Targets: 4c) I can gather, analyze and interpret data about physical and chemical properties to develop a prediction and support a claim about the type of bond in a compound (ionic, polar covalent, nonpolar covalent). (DOK 2-3) 4d ) I can describe how physical and chemical properties of substances provide evidence for our current bonding models. (DOK 1-2) Properties of Ionic and Covalent Compounds Introduction: A compound is defined as the chemical combination of two or more elements. A chemical bond is the “glue” that holds atoms of different elements together. Bonds in compounds can be classified into two general types: ionic and covalent. Ionic bonds generally occur between a metallic atom and a nonmetallic atom. The ionic bond involves the transfer of electrons from the metallic atom to the nonmetallic atom, resulting in a charge difference. The positively charged metal ion is then attracted (electrostatic attraction) to the negatively charged nonmetal ion. Covalent bonding generally occurs between atoms that are nonmetallic and it involves the sharing of electrons. Properties such as melting point, boiling point, solubility, electrical conductively, color, and odor are some of the properties that can help you distinguish ionic from covalent compounds. In this experiment, you will observe several properties of some ionic and covalent compounds and attempt to recognize some patterns among the properties. It is important to understand that the patterns are generalizations that do not necessarily apply to ALL ionic and covalent compounds. Purpose: In today’s experiment, you will observe some properties of ionic and covalent compounds. You will compare the names, formulas, solubility, electrical conductivity, and relative melting points of four KNOWN compounds. You will use the observed properties to classify the known compounds and will apply your understanding to identify several unknowns. Materials: TEST B distilled water 10 mL graduated cylinder 6 small test tubes test tube rack 6 stoppers for test tubes safety goggles lab apron 6 labeled plastic cups with lids, each containing 1 gram of the identified substance. TEST C contents of tt from Test B watch glass conductivity tester [OPTIONAL TEST D] [6 small test tubes] [test tube rack] [6 stoppers for test tubes] [99% isopropyl alcohol] [ (isopropanol, 2-propanol) ] TEST E………………… coffee can lid aluminum foil small test tube crucible tongs stop watch, if available hot plate Chemicals: NAME sucrose (table sugar) FORMULA C12H22O11 sodium chloride (table salt) NaCl sodium citrate Na3C6H5O7 4 sodium hydrogen carbonate (baking soda) NaHCO3 5 Glycerol (also called glycerine) C3H8O3 Paraffin wax C20H42 1 2 3 6 USE(S) sweetener; add texture to baked products; preservative in jams; enhances taste of food; preservative treatment of kidney stones; food additive for flavor (has a tart taste); preservative; anti-coagulant; occurs naturally in citrus fruits and berries leavening agent in cooking; cleaning; disinfectant; toothpaste; absorb odors; antacid in foods as humectant, solvent, and sweetener, filler, thickening agent, and may help preserve foods; sugar substitute; in medicine as a lubricant and humectant; in lotions; glycerine soap; in botantical extracts; used to be used in anti-freeze; candle-making; coatings for waxed paper or cloth; candy making; coating for cheese; chewing gum additive; crayons; in wax for surfboards, skis, and snowboards PLEASE – do NOT write on this paper. RETURN this paper at the end of the class period. THANKS Safety Considerations: TEST E - ALWAYS exercise caution when using hot plates. The aluminum foil will be very hot after TEST E of this experiment. Be careful. Waste Disposal: All solutions (solids dissolved in liquids) used in today’s experiment can be flushed down the sink with running water. Any solids that do not dissolve should be wrapped in a small amount of paper towel and thrown away in the regular trash can. Procedure: 1. 2. Read the procedure, being certain you understand what you will be doing in the lab. Ask questions if you don’t understand. While you are reading the procedure, you need to develop a Data table* to organize the information you will collect during this investigation. Once you have shown your teacher the data table, put on your laboratory apron and safety goggles. TEST A: GENERAL CHARACTERISTICS 3. Open each plastic container and make some general observations of each substance. Include state of matter (solid, liquid), color, texture, odor, and conductivity of the pure substance. TEST B: SOLUBILITY in WATER 4. Label six test tubes with numbers 1-6 to correspond to the substances in your data table. Place 5 mL of distilled water in each of the test tubes. Then put about ½ gram* of each of the substances into the appropriate test tube. [Remember – the cup contains 1 gram, so put ½ of the amount you have in the portion cup into the test tube.] Stopper the tubes and shake them to dissolve the solids as much as possible. Shake for one to two minutes. Do not clean up the test tubes yet – you will need them for Test C. If the substance dissolves, record this as soluble If the substance does NOT dissolve, record this as insoluble. If some of the substance dissolves, but not ALL of the substance dissolves, record this as partially soluble. TEST C: ELECTRICAL CONDUCTIVITY OF WATER MIXTURE 5. 6. Determine the electrical conductivity of any of the water mixtures where the pure substance dissolved. [If a substance did not dissolve, there is no need to test the conductivity of the water mixture.] Electrical conductivity can be tested by using a conductivity tester. Pour a small amount of one water mixture on a watch glass. Place the electrodes of the conductivity tester into the mixture and turn the tester on. If the mixture conducts electricity, the LED will light. If the mixture does not conduct electricity, the light will not go on. Use the chart on the back of the conductivity tester to determine the degree of conductivity. Record the results in your data table. Carefully rinse the electrodes and watch glass with distilled water before testing the next mixture. Rinse the test tubes, stoppers, and watch glass. Check with your teacher for the proper disposal of the mixtures. OPTIONAL TEST D: SOLUBILITY in ISOPROPYL ALCOHOL 7. 8. Place 5 mL of isopropyl alcohol in each of the test tubes. Dispose of any leftover alcohol carefully, following your teachers guidelines. Then put ½ gram of each of the solids into the appropriate test tube. [Remember – you massed out 1 gram initially… so put ½ of the amount that was originally in the portion cup into the test tube.] Stopper the test tubes and shake them for one to two minutes. If the substance dissolves, it is soluble, if not, it is insoluble. Record the results in your data table as soluble or insoluble. [Note: some substance may appear to partially dissolve. Record these as partially soluble.] Check with your teacher for the proper disposal of the solutions and the undissolved mixtures. [Take your test tubes to the hood. Pour the contents of each of the test tubes into the appropriate beaker.] Rinse the test tubes and stoppers at your sink. PLEASE – do NOT write on this paper. RETURN this paper at the end of the class period. THANKS TEST E: MELTING TIME Melting time is the amount of time necessary to melt a certain quantity of a solid. This does not give an accurate value for the melting point, but will enable you to see differences among the compounds. If the melting time is short, the substance has a relatively low melting point. If the melting time is long, the substance has a relatively high melting point. NOTE – If the substance is already a liquid, the melting point is low and there is no need to test it. 9. Locate a hot plate, plug it in, and turn it on medium. Determine the “melting time” of the solids by placing a small amount (sample about the size of a match head) of solid in an aluminum cup. (Make the aluminum cup by forming a small square of aluminum foil around the bottom of a test tube. Remove the foil and flatten the bottom of the cup.) Place the cup on the metal coffee can lid – in the appropriate spot. [NOTE: The coffee can lid has been separated into six sections, with each section labeled with a number to match the four substances to help you keep track. Once you have all six substances placed on the coffee can lid, carefully place it on top of the hot plate and note the start time. Watch the samples carefully. Whenever a sample starts to melt, immediately remove it from the coffee can lid using a crucible tong. Do NOT continue heating these substances after they have melted. Record the melting time in your data table. Continue heating the substances until they melt or until you reach 3 minutes. If a substance has not melted within the 3 minute time period, stop heating and record the melting time as > 3 minutes – which implies a high melting point. 10. 11. Once the samples have cooled, simply close the aluminum cups and discard them in a trash can. Wash your hands thoroughly with soap and water. UNKNOWN: A student tested the following unknowns and collected the following data: For ONE of the unknowns below, decide if the unknown is an ionic or covalent compound. Make a claim, support it with evidence from the data table and explain how the properties (your evidence) relate to the bonding. NAME FORMULA A B C D alum (aluminum potassium sulfate) AlK(SO4)2·12H2O phenyl salicylate (salol) (C6H4OH)(COO(C6H5) or C13H10O3 stearic acid CH3(CH2)16COOH dextrose C6H12O6 NAME B alum (aluminum potassium sulfate) phenyl salicylate (salol) C stearic acid D dextrose A TEST A TEST B TEST C TEST E White solid Does not conduct electricity Dissolves (soluble) Conducts electricity High melting point White solid Does not dissolve (insoluble) White solid Does not dissolve (insoluble) White solid Dissolves (soluble) Does NOT conduct electricity Does NOT conduct electricity Does NOT conduct electricity low melting point low melting point low melting point USE(S) deodorant; water purification, in styptic pencils (stop bleeding due to small cuts when shaving); pickling; once used in sunscreens; manufacture of some polymers, lacquers, adhesives, waxes and polishes. production of detergents, soaps, and cosmetics such as shampoos and shaving cream products simple sugar used in baking goods; added to artificial sweeteners as a filler. PLEASE – do NOT write on this paper. RETURN this paper at the end of the class period. THANKS Post Lab Discussion: You have just recorded several properties of some ionic and covalent compounds. Up until now, you have not identified the substances as ionic or covalent. Ionic compounds are generally made up of metallic and nonmetallic elements, with the metal giving up electrons to the nonmetals. Covalent compounds are generally made up of atoms that are nonmetallic, with the atoms sharing electrons. You will need to refer to the ‘BACKGROUND INFORMATION’ in this lab, your notes, a textbook or another resource to help you in determining whether the compounds used in this experiment are ionic or covalent. It is important to emphasize that some of the results of the experiment may not reflect particular patterns. Post Lab Analysis: Answer these questions in complete sentences so that the initial question is obvious. (1) After reading the background information (or other resource(s)), construct a Venn Diagram for Ionic and Covalent Compounds. Place at least 10 of the following descriptors in your Venn Diagram: (a) contain metal and nonmetal atoms (b) contain nonmetal atoms (c) electrons are transferred from metals to nonmetals (d) electrons are shared (e) low(er) melting point (f) high(er) melting point (g) soluble in water (h) not soluble in water (i) solids do not conduct electricity (j) conduct electricity when dissolved in water (k) do not conduct electricity when dissolved in water (l) tend to be solids only (m) tend to be gases, liquids, or soft solids (n) tend to have distinct odors (o) tend to have a crystal structure Feel free to add additional descriptors to your diagram. Use your lab observations and understanding, answer the following questions with a CLAIM, some EVIDENCE, and – if possible – an EXPLANATION. (2) (3) (4) Which ONE known substance are you most sure is ionic? Why? Which ONE known substance are you most sure is covalent? Why? Which ONE known substance are you not sure if it is ionic or covalent? Why? (5) Place each of the six substances from this lab into your Venn diagram by writing each formula in the correct part of the diagram. Conclusion: Write a paragraph that summarizes the big ideas from this lab. Include and underline the following terms in your paragraph: Get the paragraph stamped by your teacher. Ionic compound Metal Physical Properties Electron(s) Share Transfer Covalent Compound Non-metal PLEASE – do NOT write on this paper. RETURN this paper at the end of the class period. THANKS Background Information: Ionic compounds (or salts) are formed when metals transfer electrons to nonmetals. The loss of electrons by the metal atom transforms it into a positive ion. The gain of electrons by the nonmetal atom transforms it into a negative ion. The positive and negative ions are attracted to each other because of their opposite charges. A salt is really a network of positive and negative ions that are stacked in a specific crystalline structure due to their mutual attractions. In a covalent compound, atoms share electrons. Covalent bonds are usually formed between nonmetal atoms, which have more valence electrons than they are energetically capable of losing. When two nonmetal atoms meet they do not tend to completely transfer electrons (as a metal would do to a nonmetal); instead, they tend to share. One pair of electrons makes a covalent bond, and since both atoms “want” that pair of electrons, they stick together as long as the pair is shared. Both types of chemical bonds exist because of atoms trying to satisfy the octet rule. The octet rule says that atoms gain, lose, or share electrons in an attempt to achieve the same electron configuration as one of the noble gases (which usually have 8 valence electrons – hence the word “octet”). Noble gases have the most stable arrangements of electrons; this explains why they so seldom participate in chemical reactions. If you know the chemical formula of a compound, you can predict whether it contains ionic bonds, covalent bonds of a mixture of bond types. Nonmetals bond to each other via covalent bonds while oppositely charged ions, such as metals and nonmetals, form ionic bonds. Some compounds have a metal and several non-metals. These compounds (i.e. MgSO4 or Na3PO4) may have both ionic and covalent bonds. But, how do you know if a compound is ionic or covalent just by looking at a sample? This is where the properties of ionic and covalent compounds can be useful. Because there are exceptions, you need to look at several properties to determine whether a sample is ionic or covalent, but here are some characteristics to consider: Most crystals are ionic compounds. This is because the ions in these compounds tend to stack into crystal lattices to balance between the attractive forces between opposite ions and the repulsive forces between like ions. Covalent or molecular compounds can exist as crystals, though. Examples include sugar crystals and diamond. Ionic compounds tend to have higher melting and boiling points than covalent compounds. Ionic compounds tend to be hard and brittle while covalent compounds tend to be softer and more flexible. Ionic compounds conduct electricity when dissolved in water while covalent compounds typically don't. This is because covalent compounds dissolve into molecules while ionic compounds dissolve into ions, which can conduct charge. [Resource: http://chemistry.about.com/b/2013/07/25/properties-of-ionic-and-covalent-compounds.htm]