Lab Phase Changes

Lab Phase Changes Scientific Problem: What happens to the temperature of a substance during a phase change (increase, decrease, stay the same, etc.) Background: 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. Physical ChangeChanges physical properties ONLY (ex mass, length, etc.) Chemical ChangeChange in chem properties→ chem reactions (burning, rusting, fizzing, etc.) Phase ChangeFrom 1 phase to another (ex Solid→ Liquid) MeltingMolecules moving faster & farther apart FreezingMolecules moving slower and closer together VaporizationMolecules moving faster & farther apart BoilingOnly at specific temp Water 100℃ EvaporationRange temp Water 1 - 99℃ CondensationMolecules moving slower and closer together Sublimation you skip liquid phase Materials 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. Water Freezer Beaker Thermometer Rubber Stopper Ring Stand Wire Gauze Clamp Bunsen Burner Plastic sandwich bag Rubber band Timer Procedure: Before Class 1. Add a small amount of water to the plastic sandwich bag. The amount of water needs to be small enough so that it will fit into the beaker after freezing (remember the water will expand when it freezes). 2. Suspend a thermometer in the bag of water and attach the bag to the thermometer using the rubber band. 3. Place the water bag thermometer combo in the freezer and allow it to completely freeze. In Class 1. Set up the ring stand, wire gauze and Bunsen burner. 2. Put enough water in the beaker so that it can completely submerge the ice water bag without overflowing. 3. Place the beaker on the wire gauze of the ring stand. Place the ice water bag in the beaker of water and use a clamp to secure the bag. Record the starting temperature of the ice in the bag. 4. Turn on the Bunsen burner. 5. Carefully move the Bunsen burner under the wire gauze and adjust your flame further if necessary. Start timing immediately after you place the Bunsen burner under the wire gauze. 6. Measure and record the temperature of the ice water bag every 30 seconds. Also be sure to record any observations - specifically what phase(s) are present (ex solid only, solid and liquid, etc.). 7. Continue to heat the beaker of water until all of the ice in the bag is melted. 8. Turn off the Bunsen burner (at the local gas jet) and allow the materials to cool. 9. Once the equipment has cooled, clean up your station. Variables • • • independent phase change dependent temperature controlling heat source, substance using, container holding the substance Hypothesis If we melt ice (solid water) then the temperature will not rise, because if you heat ice it does not change in a phase change. Conclusion: • • • • • Conclusion statement (answer to scientific problem): During a phase change the temperature does not change. My conclusion supports my hypothesis Examples of data support: o Example 1: The temperature does not rise during a phase change o Example 2: melting started at 0 and did not change until 2.5 min therefore the data did not change. Possible sources error (specific examples – not just human or measurement error)? o Possible Error 1: hight of fire. o Possible Error 2: where the bunsen burner was placed Examples of possible future research: o Example 1: bigger piece of ice o Example 2: use different heating source Discussion Questions 1. The water in the sandwich bag went through freezing. What did you have to do to cause this phase change to take place? Take heat away How did the molecules of the water change as they went through freezing? they moved slower and closer 2. During this experiment, the ice in the sandwich bag went through melting. What did you have to do to cause this phase change to take place? apply heat How did the molecules of the water change as they went through melting? they moved faster 3. Are phase changes are physical or chemical changes? physical Explain your answer to the previous question: you can change it back to the original stage 4. What is the difference between boiling and evaporation? evaporation is from 1 to 99 degrees celsius. boling has to be 100 degrees or higher 5. What happens to molecules when you add heat to them? they move faster What happens to molecules when you take heat away from them? closer and slower 6. Name the Bunsen burner part for the following: a. Adjusts height of flame: daisy wheel b. Adjusts color of flame:chimney c. Adjusts stability of flame:chimney and daisy wheel d. Adjusts amount of gas going through the Bunsen burner: daisy wheel e. Adjusts the amount of oxygen going through the Bunsen burner:chimney 7. Describe a properly adjusted Bunsen burner flame: blue flame with blue cone 8. Describe the local gas jet when the gas is turned off: It's in a right angle Describe the local gas jet when the gas is turned on: its in the line or a lowercase L 9. What is the best way to turn off the Bunsen burner? use the handle on the gas to turn it off. Why? then you do not have to touch the hot part of the bunsen burner