Lab: Properties of Polar and Nonpolar Substances

Transcription

1 Lab: Properties of Polar and Nonpolar Substances Purpose: To explain the interactions of matter in relation to polarity. Stations 1 and 2 - il and water do not mix As a metaphor, oil and water are often used to explain why relationships between opposites are difficult. In this lab you will trace this metaphor back to its source the nature of oil and water, solutes and solvents, and why some substances do not dissolve in or mix well with others. We will be looking at the polarity of substances and attractions between molecules and how these influence solubility. Background: A solution is a homogeneous mixture of two or more substances. The composition or concentration of a solution can be changed by changing the amount of the solute (the minor component) dissolved in a given amount of the solvent (the major component). Solubility is a characteristic property of a pure substance and can be used to help identify different substances. Thus, a chemistry handbook will usually report the solubility of a substance in different solvents along with other physical properties such as melting point, density, etc. When a solute dissolves in a solvent, the attractive forces acting between solute particles and those between solvent molecules must be broken and replaced by new attractive forces between the solute and solvent. The nature and strength of the attractive forces among solute and solvent particles influence whether a solute will dissolve in a solvent. ovalent compounds consist of molecules, rather than ions. The physical properties of a molecular compound, including solubility, depend on the polarity of the molecules. The polarity of a compound determines the types of intermolecular attractive forces between molecules and is an important factor influencing the solubility of solutes and solvents. At station 1 you will be using water, paint thinner, and isopropyl alcohol as solvents. You will be using ul 2 (copper (II) chloride) and I 2 (Iodine) as solutes. l 4 (carbon tetrachloride) has properties very similar to that of paint thinner, but is a carcinogen (causes cancer). 3 (methanol) has properties very similar to that of isopropyl alcohol, but is highly toxic. We will use the safer solvents in the lab, but you will be able to draw conclusions about polarity by looking at the Lewis structures for the more dangerous (but much easier to draw) compounds. PreLab: For each structure use the periodic table of electronegativities to determine if each bond is polar or nonpolar and draw a dipole arrow, if applicable. l l l l l - I I u 2+ l -

2 List the 3 solvents in order of increasing polarity opper II hloride is a(n) (circle one) ionic polar covalent nonpolar covalent compound. Iodine (I 2 ) is a(n) (circle one) ionic polar covalent nonpolar covalent compound. : Station 1 Solubility of Solids 1. btain 6 test tubes. Fill two test tubes half full with water. Fill two test tubes half full with isopropyl alcohol. Fill two test tubes half full with paint thinner. 2. Make two sets of test tubes: a complete set contains one containing water, one containing isopropyl alcohol, and one containing paint thinner. 3. Using one set of 3 test tubes: put a small amount (less than a match head sized piece) of iodine into each test tube. Swirl or tap. Swirl or tap some more. 4. Judge by the color of the liquid whether the solid is insoluble, partially soluble, or very soluble. 5. Record all data on the table provided. 6. Empty the test tubes into the proper waste containers. Wash with soap and water. 7. Using the other set of 3 test tubes: obtain enough copper (II) chloride crystals to fill the tip of a scoopula. Put this much of the solid into each of the 3 test tubes. 8. Judge by the color of the liquid whether the solid is insoluble, partially soluble, or very soluble. 9. Record all data. 10. Empty the test tubes into the proper waste containers. Wash with soap and water. N PAINT TINNER DWN TE DRAIN R IN TE SINKS!! Station 2 Mixing Liquids 1. Put 4 ml of water into 1 test tube, then add 4 ml of paint thinner. Swirl or tap the test tube. Do they mix or separate? Record your observations. 2. Put 4 ml of water into a 2 nd test tube, then add 4 ml of alcohol. Swirl or tap the test tube. Do they mix or separate? Record your observations. 3. Put 4 ml of paint thinner into a 3 rd test tube, then add 4 ml of alcohol. Swirl or tap the test tube. Do they mix or separate? Record your observations. 4. Dispose of all liquids according to your teachers instructions. N PAINT TINNER DWN TE DRAIN R IN TE SINKS!!

3 Station 3 Evaporation Below are the Lewis structures for acetone (ingredient in most nail polish removers), ethyl alcohol (ethanol), and water. Determine the polarity of each bond and note NLY the polar bonds on the diagram, using a dipole arrow. 1. At exactly the same time, place 1 drop of each liquid on your lab table. Watch them evaporate. 2. List the liquids below, from first to evaporate to last to evaporate: A) B) ) Station 4 Bending Water 1. Run a small stream of water from the faucet. 2. Place the unrubbed balloon near the stream. Do you notice anything occurring? 3. Rub the FAE side of the balloon vigorously against your clothes or hair. Bring it close to, but not touching, the stream of water. Record your observations in the analysis section. Station 5 Magic Sand 1. Fill up 2 beakers about half-way with water. 2. To the first beaker, add a couple spoonfuls of magic sand. To the second beaker, add a couple spoonfuls of regular sand. 3. Stir each mixture with a stirring rod. 4. When you are finished with your observations, pour off as much water as possible into the water beaker without losing any sand. Then dump the regular sand into the designated tray. Scoop the magic sand back into the labeled beaker. 5. Answer the analysis questions. Station 6 Penny Stacker 1. Place two pennies on a paper towel. 2. n one penny, count how many drops of ethanol fit in the penny before the oil spills onto the paper towel. 3. n the other penny, count how many drops of water fit on the penny before the water spills onto the paper towel.

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5 Name: Date: Per. Student# DATA TABLE Analysis: Station 1 Solubility of Solids Station 2 Mixing Liquids 1. Polar/Ionic solids dissolve in (circle one) polar nonpolar liquids. 2. Nonpolar solids dissolve in (circle one) polar nonpolar liquids. 3. Polar liquids (circle one) mix do not mix with nonpolar liquids. 4. Using what you have learned from this lab, explain why oil and water do not mix. Be sure to include the terms: polarity, attractive forces, molecules.

6 Station 3 Evaporation 5. The first liquid to evaporate had (circle one) the most the fewest polar bonds. 6. Use what you know about intermolecular attractions to explain this: Station 4 Bending Water 7. Sketch the behavior of the water with the balloon 8. By charging the balloon you are collecting electrons on the side of the balloon that was rubbed. Use this information, along with the knowledge that water is a polar molecule, to explain which part of the water molecule is attracted to the balloon. You may use words or sketches, but any explanation should include knowledge about the polarity of a water molecule.

7 Station 5 Magic Sand 9. Describe the difference between the interactions of water and the two types of sand. 10. Explain how you think magic sand works. Station 6 Penny Stacker (cohesiveness of molecules) 11. ow many drops of ethanol fit on the penny? 12. ow many drops of water? 13. Why were you able to fit more drops of one liquid on the penny than the other? onclusion Questions 14. What is a polar bond? 15. List 3 properties affected by the polarity of a molecule in this lab. a. b. c. 16. Polar compounds have (circle one) stronger weaker attractions between molecules. That means that they will evaporate at (circle one) higher lower temperatures. This is because of the attractions between the polar regions of each molecule.