Properties of Solids Lab

Lab-Properties of Solids/ Bond Types Safety goggles must be worn at all times Introduction: Groups of atoms are held together by attractive forces we call chemical bonds. Why are chemical bonds important? The type of chemical bond that occurs in a molecule or substance in part defines its properties. For example, consider sodium chloride (NaCl) and hydrogen chloride(HCl). Both substances contain chlorine, but NaCl is the white solid crystalline substance sprinkled on French fries, and HCl is a foul smelling gas (note: when this gas is dissolved in water, it forms a solution known as hydrochloric acid. This is the acid that your stomach uses to digest food.) How can this be if both materials have chlorine in them? The chemical bonding that takes place in NaCl is different than that in HCl. This gives NaCl and HCl very different structures, appearances, and properties. An ionic compound is formed when a metal loses an electron to a non-metal to form charged cations and anions. The oppositely charged ions arrange themselves in a tightly packed, 3-D structure called a crystal lattice. Another type of attractive force between atoms, covalent bonding, occurs when two non-metals share electrons. Metallic bonding occurs between metal atoms. The valence electrons in a metallic bond are free-floating and are shared between the metal atoms (the so-called “sea of electrons”). Purpose: To investigate the physical properties of common solids and to see if a substance’s bonding type has any relationship to its properties observed in the lab. Materials: Aluminum metal –Al Sodium Chloride -NaCl Sucrose -C12H22O11 Ice - H2O (s) 4 test tubes 1 test tube holder Hot hands Distilled water Bunsen burner Stir sticks Well Plate Conductivity tester Mortar and Pestle Procedure: 1. Place a small scoop of each substance in the well plate and test the conductivity of each substance in it’s solid state. The conductivity tester will determine if the substance conducts electricity. (Please make sure to turn off the device when finished.) 2. Add a few drops of distilled water to each well and record if the substance dissolves in water or not- we call this solubility. 3. Test the conductivity of each substance in the well now that it is submerged in the water. Record your results. 4. Place a small amount of each solid into a test tube. Using a test tube holder, place it over the flame and melt it. Record the amount of time it takes to melt the ice. NOTE: The Bunsen burner reaches over 1000◦ C. Some substances may not melt using the Bunsen Burner, therefore their melting point is higher than 1000◦ C. STOP TIME AT THE FIRST SIGN OF LIQUID 5. Place each substance (one at a time) in the mortar and pestle. Grind up the substance and record how brittle it is (how easily it breaks up). Wipe out the mortar and pestle with a paper towel between each substance. Data/ Observations: Physical Properties Sucrose C12H22O11 Ice H2O (s) Epsom Salt (MgSO4) Sodium Chloride (NaCl) Aluminum (Al) Type of chemical bond (based on chemical formula) Conductivity (solid) Solubility Conductivity (dissolved) Melting Point (time it takes) Brittleness (yes or no) Calculations/ Analysis: 1. Summarize your lab results, complete the following table: Properties Substances with IONIC bonds Substances with COVALENT Bonds Substances with METALLIC Bonds Melting point (high/ med/ low?) Soluble in water (yes/ no?) Conducts electricity (yes/ no?) Questions for Discussion: 1. In order for a substance to conduct electricity, it must have free-moving charged particles so that the electricity (which is moving electrons) can flow. a) Explain the conductivity results observed for sodium chloride in the solid state and in aqueous solution (which means dissolved in water). b) Use your knowledge of metallic bonding (or the information in the introduction of this lab) to explain why metals conduct electricity. c) You must choose between two potentially horrible options- explain which one you’d choose and why based on this lab. 1) Sit in a bathtub filled with distilled water in which a hair dryer (that’s plugged in) has been submerged. 2) Sit in a bathtub filled with salt water in which a hair dryer (that’s plugged in) has been submerged 2. Ionic substances are brittle & metallic substances are malleable. Explain how the different bond types lead to this characteristic. Conclusion: Read back through the introduction and purpose of this lab and then write a 3 sentence summary that highlights what you accomplished during this activity, your results, and any errors that were made.