Classifying Solids Using Physical Properties Scientists classify matter according to physical and chemical properties. To do so, they conduct many qualitative analysis tests on different substances and then group the substances into categories based on properties. In this investigation, you will explore and identify the physical properties of two different classes of solids: ionic and molecular. Then you will use the established criteria to classify an unidentified solid provided by your teacher. The physical properties that you will explore are conductivity (ability to conduct electricity), hardness (resistance to being scratched), melting point, and solubility (ability to dissolve in water). Purpose: To determine how ionic and molecular solids compare on the basis of conductivity, solubility, hardness, and melting point? Hypothesis: From its chemical formula, predict whether each solid (potassium iodide, sodium chloride, ammonium chloride, benzoic acid, sucrose, camphor) is ionic or molecular. Explain your Prediction. Materials: potassium iodide, KI(s) sodium chloride, NaCl(s) sucrose, C12H22O11(s) camphor, C10H16O(s) low-voltage conductivity apparatus 2 test tubes test-tube rack distilled water scoopula stirring rod 10-mL graduated cylinder 4 watch glasses unidentified solid samples X and Y microtray Procedure: Place a small amount of each chemical into a numbered well in the microtray. Perform parts 1-5 of the experiment as a comparison between an ionic compound and a molecular one; KI and C12H22O11, NaCl and C10H16O, Unknown X and Y. Part 1: Testing for Solubility 1. Place the test tubes in the test-tube rack. 2. Using the masking tape, label the test tubes sample one and two. 3. Pour 10 mL of distilled water into each test tube. 4. Add a small amount (fill the tip of the scoopula) of each solid to its respective test tube. 5. Using a stirring rod, stir the mixtures. Observe how completely each solid dissolves. Record your observations in a table. 6. Keep the solutions for Part 2 of the investigation. Part 2: Testing for Conductivity 7. Fill a beaker with 10 mL of distilled water. Test for conductivity using the low-voltage conductivity apparatus. 8. Place each solution from Part 1 into a beaker. Test the conductivity of each solution. Record your observations in your table. 9. Follow your teacher’s instructions for disposing of the solutions. Part 3: Testing for Hardness 10. Using the scoopula, place a few small crystals of each solid on individual watch glasses. 11. Using the scoopula, attempt to crush a few of the small crystals between the scoopula and the watch glass. 12. Rank the relative hardness of each sample. Record your rankings in your table. Part 4: Melting Point This is a comparison to see which substance melts first. 13. Place a small sample each sample into separate test tubes. Hold both samples in the Bunsen burner flame until one of them melts. Record the melting points as low or high. Part 5: Classifying an Unidentified Sample 14. Obtain unidentified sample Xand Y from your teacher. Test the sample for solubility in water, conductivity, and hardness, melting point as you did in steps 1 to 13. Record your observations in your table. Conclusion: Answer the purpose. Discussion/Analysis: 1. Use your observations to group the first six solids into two categories. 2. Briefly summarize the physical properties of each category. 3. Based on your summary of the physical properties of the two categories, decide to which category your unidentified sample belongs. Give detailed reasons for your choice, using the different properties of matter that you investigated. 4. Are the physical properties that you studied in this investigation sufficient for classifying the solids into two categories? What other physical properties could you investigate? 5. Evaluate your Prediction based on your Analysis. Inv Errors: Suggest possible sources of error in the Procedure, and explain their effects on your results. How could you modify the Procedure to reduce these sources of error?