Working in the Chemistry Laboratory Accelerated Chemistry I Introduction: One of the most important components of your chemistry course is the laboratory experience. Perhaps you have done experiments in other science courses, so you are somewhat familiar with some of the lab equipment. The chemistry laboratory is unique, however. There is a great deal to be learned about the equipment and safety procedures in a chemistry lab. A number of important procedures need to be mastered in order for you to be successful in the later experiments in this course, you need to know: 1. how to use a lab burner 2. how to manipulate glass tubing 3. how to handle solid chemicals and solutions 4. how to heat materials safely 5. how to use and read instruments such as balances, thermometers and graduated cylinders with the proper level of precision. In this experiment you will have a chance to learn all of these lab techniques while doing an experiment involving an important chemical reaction. Limewater is a solution of calcium hydroxide, Ca(OH) 2, dissolved in water. Limewater is used as a test for the presence of carbon dioxide. When CO 2 is bubbled through limewater, a chemical reaction occurs which produces a solid product. When a solid product is formed in a liquid solution it is called a precipitate. Materials and Reagents thermometer 2-250 ml beakers magnesium ribbon ring stand stirring rod glass tubing paper towels ring 2 Erlenmeyer flasks (125 ml) 100 ml graduated cylinder calcium hydroxide funnel 1-one hole stopper to 1M HCl (hydrochloric acid) triangular file lab burner fit Erlenmeyer flasks sodium carbonate spark lighter balance 1-two hole stopper to glycerin metric ruler filter paper fit Erlenmeyer flasks funnel holder glass tubing Day One - Procedure (Part 1): 1. Put on safety goggles. These must be worn throughout the lab period. 2. Most lab burners are constructed in a similar fashion. There is an inlet for the gas, an adjustment for the amount of gas, and an adjustment for the amount of air (See Figure on right). A proper mix of air and gas will yield a faint blue flame for maximum heat and minimum soot. 3. Examine your burner before your try to light it. Identify the gas and air adjustments. To start the flame turn the air adjustment to allow as little air in as possible. Use a match or a spark lighter to light the burner by turning on the flame and holding the lit match above the barrel of the burner.
Working in the Chemistry Lab page 2 4. Adjust the flame to a blue color without a roaring sound by changing the amount of air and amount of gas. Now turn the air too low and too high. Observe the changes in the flame. Next turn the gas adjustment to rich and too lean. Observe the changes in the flame. Finally set the burner to optimum adjustment. Turn the burner off and go to part two of the experiment. Procedure (Part 2): 1. Obtain a piece of glass tubing that is at least 45 cm long. Cut the tube into two pieces, one 15 cm and the other 30 cm as follows: Place the tubing on a flat surface and measure with a metric ruler. Scratch the tube at the point to be cut using the triangular file. Only pull the file across the tube surface once. Wrap the tube in paper towels and with the scratch on the side of the tube away from you, place your thumbs on the back side of the tube near you and push with your thumbs to snap the tube. 2. Smooth the ends of the tube by fire-polishing: Light the burner and place one end of a tube in the flame. Rotate the tube so the heating is even. You should notice the tube end becoming smooth. Do not leave the glass in the flame for too long or you will melt and seal the end. Make sure to fire polish the end of each tube. 3. When cool enough hold one end of a tube in each hand. Place the center of the tube in the hottest part of the flame and rotate the tube until you feel the center getting soft. Quickly bend the tube to an approximately 90 angle and remove the tube from the flame. Repeat with the other 30 cm tube. 4. Allow the tubes to cool. Then place two drops of glycerin into one of the holes of a two hole stopper. The glycerin acts as a lubricant for the glass tubing. Protecting both hands with paper towels, carefully place one of the bent tubes into the stopper far enough that it almost reaches the bottom of the Erlenmeyer flask when the stopper is placed in the flask. Repeat the process with the other tube and the one hole stopper. Examine the last figure in the lab procedure to see how far the tubes should be pushed into the stoppers. The 30 cm tube goes in the two hole stopper and the 15 cm tube goes in the one hole stopper. Procedure (Part 3): 1. In order to make limewater you must use the lab balance. To zero the electronic balance press the tare button or zero bar once. Wait until the balance reads all zeros. 2. When you find the mass of solid chemicals it is important that you do NOT place the chemical directly on the balance. Sometimes you will mass into a piece of laboratory equipment or as you will this time, you mass onto a piece of scrap paper and then transfer the dry chemical to a piece of laboratory equipment. 3. Place a piece of scrap paper on the balance and re-zero the balance. Add Calcium hydroxide to the paper until the mass is approximately 1.25 grams. Transfer the Ca(OH) 2 to a dry 250 ml beaker. 4. Place the beaker in your lab drawer and clean and wash your bench. Lock your lab bench drawer. Wash your hands before you leave the classroom.
Working in the Chemistry Lab page 3 Day Two - Procedure (Part 3): 5. Put on safety goggles. These must be worn throughout the lab period. Using the graduated cylinder, place 150 ml of distilled water into the 250 ml beaker with the Ca(OH) 2. Graduated cylinders are designed to be read correctly only if the bottom of the meniscus is the point where the volume is recorded. A meniscus is the slight curve that appears because the water is slightly higher on the surface of the glass and therefore lower in the middle. Stir the solution slowly. 6. Ca(OH) 2 is difficult to dissolve. Heating will speed up the dissolving process. Set up the ring stand with ring (See figure above right). Place the wire gauze in the ring and make sure it is level and secure. Place the beaker on the wire gauze and heat gently for 5 min. with constant stirring. After 5 mins. turn the Bunsen burner off. Using beaker tongs, place the beaker on the bench top to cool. 7. While the solution is cooling, set up the funnel with filter paper. Filter paper is supplied in a circular shape. Fold it in half once and again. (See Figures below and below right). Open the filter paper up so 3 sides are on one side and a single side is on the other forming a cone. Moisten the filter paper with distilled water and place it in the funnel 8. Pour the solution into the filter funnel using the stirring rod to guide the solution to the filter (see figure below right). Do not fill over the top of the filter. Make sure your filtrate (the stuff coming through the filter) is clear. If not repeat steps 7 and 8. Procedure (Part 4): 1. Place just enough of the clear limewater into an Erlenmeyer flask so that just the bottom of the bent arm tube in the stopper is covered when placed firmly in the top of the flask. 2. With the stopper in the top of the flask, blow gently into glass tubing. Continue until you notice a change in the limewater. Write your observations on the report sheet.
Working in the Chemistry Lab page 4 Procedure (Part 5): 1. Rinse out the flask just used and add fresh clear limewater as in step one of part four. 2. In the other flask place 35 ml of 1.0 M hydrochloric acid (HCl). Connect the two bent arm glass tubes with a short piece of rubber or plastic tubing. (See Figure above). 3. Measure the temperature of the HCl and record it on the report sheet. Rinse the end of the thermometer after you remove it from the HCl. 4. Read this step completely before proceeding. Take a 1 cm piece of Mg ribbon and drop it into the HCl. Quickly place the second stopper on top of the flask with the HCl. Watch the reaction in the HCl flask and record your observations of the changes in both flasks in the report sheet. 5. As soon as the reaction stops (no more signs of a chemical change occurring) remove the stopper from the HCl flask and record the temperature of the acid. Record this on the report sheet. 6. Rinse out both flasks and repeat steps 1, 2, and 3 of part 5. 7. Instead of Mg add 2 g of Sodium Carbonate to the acid and repeat step 4 and 5. 8. Clean and return all equipment to its proper place of storage. 9. Clean up your lab bench and wash your hands when finished with the experimental portion of the lab.
Name Date Working in the Chemistry Laboratory Accelerated Chemistry I Prelab Questions - Complete before starting experiments 1. What is the purpose of mixing the air with the gas when using a lab burner? 2. Describe how glass tubing is cut in the chemistry lab 3. What is fire-polishing? 4. What is the purpose of using glycerin when inserting glass tubing into a rubber stopper? 5. Read the mass shown on the balance diagram below. Record all the certain plus one uncertain digits 6. Read the temperature shown on diagram of a metric thermometer below. Record all the certain plus one uncertain digits 7. What is a precipitate 0 10 20 8. Read the volume in the graduated cylinder shown at the right. Record all the certain plus one uncertain digits. 20 19
Data and Observations Part 4 Observation from step 2 Part 5 HCl/Mg Reaction Temperature Before Temperature After What happens in the reaction flask? What happens in the limewater flask? HCl/Sodium Carbonate Reaction Temperature Before Temperature After What happens in the reaction flask? What happens in the limewater flask? Analysis and Conclusions: 1. In part 5, was carbon dioxide produced in either reaction? How do you know? 2. Were the reactions endothermic or exothermic? 3. Why was it necessary to filter the limewater before using it in parts 4 and 5? 4. Why did you use a piece of paper when massing the solid on the balance? Synthesis 1. If you were to find the mass of the HCl and the mass of the Mg strip before the reaction, how would that mass compare with the mass of the material that remained in the flask after the reaction was complete? If you could contain the gas that was produced, how would the before and after masses compare? 2. Review the procedure and list all the SI units that were used in the experiment. 3. Matter in three different phases was observed in this experiment. Give two examples from the experiment of each. Solids? Liquids? Gases?