Unit Name
Lab #1
Laboratory Procedures
Background: The best way to become familiar with the various pieces of equipment you will use in chemistry is to actually use them in the laboratory. This lab is divided into several parts. You will learn how to adjust the Bunsen burner, use a balance, handle solids, measure liquids, and filter a mixture and measure temperature and heat. The emphasis here is on how to use the apparatus safely. It is important that you develop good laboratory techniques to insure safety in the lab for you and your classmates.
Safety Precautions – appropriate safety precautions as outlined in safety instructions should always be followed. Please refer to your safety handout to refresh your understanding before beginning the lab. The following reminders apply to this lab, but follow all rules all the time.
Always wear safety goggles and a lab apron to protect your eyes and clothing
Use caution when handling all laboratory chemicals
Use appropriate precautions for glass; follow directions for disposal of any broken glass
Confine long hair and loose clothing in the presence of open flame
Procedure 1: The Bunsen burner
The Bunsen burner will be our primary heat source for our investigations throughout the year. Let us examine the burner in order to learn how to most effectively and safely use this important piece of equipment.
Step 1: Refer to the diagram in figure A as you identify the parts of the burner.
The gas inlet in the base of the burner admits gas from the rubber tubing attached to the gas source (in our lab, the desktop gas jets). The gas inlet has adjustable openings that admit air to the gas stream. The gas and air are mixed as they travel up the barrel of the burner. Our burners have an adjustable needle valve at the base of the burner to regulate the flow of gas into the burner. Although the burner can be completely turned off by closing this valve, the gas should be turned off at the gas valve, not just the needle valve, when not in use.
Step 2: When lighting the burner take care not to cause a sudden ignition that could result in accidental combustion. Insure that the needle valve at the base of the burner is slightly open. If using a sparker, hold it over the top of the barrel. Open the desktop gas jet fully (when the handle is perpendicular to the nozzle the jet is fully closed, when the handle is parallel to the nozzle, it is fully open) and ignite. The height of the flame can be adjusted by regulating the gas flow using the needle valve adjustment knob on the bottom of the burner.
Step 3: Insure proper burning. When you have a very low flame, the ports that admit air should be regulated to insure that the flame is not burning inside the barrel (you will see flame coming out the bottom of the burner). If this happens, you need to immediately turn off the gas valve, adjust the air ports (by turning the barrel of the burner) and begin again.
Step 4: Experiment with opening and closing the ports and see the effect on the flame. Using forceps or crucible tongs, hold an evaporating dish in the tip of the flame for a few minutes with the ports completely closed, then set it on your wire gauze on the desktop and allow it to cool. Examine the bottom of the dish, describe the results and suggest a possible explanation.
Step 5: There are two important indicators that will give you information about the burning efficiency of your flame. The hottest, most efficient flame is mostly blue with a light blue cone at the center. If your flame is primarily yellow, this means that too much air is being mixed into the gas stream. To adjust the mixture, turn the barrel of the burner to regulate the size of the ports that admit air into the barrel. Once your mixture is adjusted properly, use your forceps to insert a 10 cm piece of copper wire into the flame just above the barrel. Lift the wire slowly up through the flame. Where is the hottest portion of the flame located? Hold the wire in this part of the flame for a few seconds and observe what happens.
Step 6: Shut off the burner, clean the evaporating dish and put away the burner. Think about what you observed in steps 3 and 4. Why is the blue flame preferred over the yellow flame for laboratory work?
Procedure 2: Handling and measuring solids
Step 1: Before using any chemical, check the label to insure that you have the correct substance. Try to remove only the amount that you will use. Solids are usually kept in wide mouthed bottles. A spatula is used to dip out the solid.
Step 2: We will use a balance to obtain a specified amount of sodium chloride. Never place hot objects or chemicals directly on the balance, always use weighing paper or a glass container. We will remove 10.00g of sodium chloride from the stock container and place it in a test tube. Place a piece of weighing paper on the electronic balance. The balance will most likely not read 0.00. In order to accurately measure the chemical you can either record the weight of the paper and subtract from the total, or you may simply hit the tare button to reset the reading to zero. Use a spatula to remove a quantity of sodium chloride from its bottle and place the quantity on the piece of weighing paper. Add or remove bits of the solid using the spatula until the desired amount is reached. Once you have 10.00g, roll the paper into a cylinder and slide it into a test tube, then tap the paper gently and the solid will slide down into the test tube. If you have included the weight of the paper, remember to subtract it from the final weight.
Step 3: This time we will remove 15.0g of sodium chloride and place it in a 50ml beaker. Since the opening of the beaker is larger than the test tube, we can transfer the chemical directly to the beaker. Place the beaker on the balance and either record the weight or tare the balance. Add sodium chloride to the beaker until the desired amount is reached. If necessary, subtract the weight of the beaker from the total to get the amount of sodium chloride.
Step 4: Now obtain 10 pennies from your assigned decade. Find the mass of each penny.
Procedure 3: Handling and measuring liquids
Step 1: For most of our use in the laboratory, a graduated cylinder will provide the needed accuracy in liquid measurement. The cylinders are usually graduated in milliliters and may have a second column of graduations reading from top to bottom. Examine your cylinder to familiarize yourself with the markings. Beakers and flasks have approximate markings for more qualitative uses. Fill a 100ml beaker to the 60ml marking with water. Now pour the water into a graduated cylinder and record its measurement more accurately. Notice that the surface of the water in the cylinder is slightly curved and forms a concave surface since the water wets the glass of the cylinder. This curved surface is called a meniscus. Read the measurement at the bottom of the meniscus.
Step 2: Fill your graduated cylinder about one third full of water. Read the volume. Gently slide all ten pennies into the cylinder. Read the volume of the water and pennies to determine the volume of 10 pennies. Find the average volume for one penny
Step 3: For more accurate liquid measurement, we can use a pipet (for relatively small amounts) or a buret. Burets are used for delivery of any desired quantity of the liquid (up to the capacity of the buret).
Obtain a buret, ring stand, buret clamp and a 250 ml beaker
Clamp the buret in position on the ring stand
Place the beaker under the tip of the buret to catch the liquid as it is released
Pour a quantity of liquid from a beaker or Erlenmeyer flask into the buret (insure that the stopcock on the buret is closed)
Open the stopcock and release a small volume of water, until the tip below the stopcock is filled and the level of the liquid in the buret is within the scale.
Read the level of the liquid in the buret. Open the stopcock and dispense a small amount of water. Close the stopcock and read the new level of the water. The exact amount of water released is the difference between the two readings.
Step 4: Dispense exactly 25ml of water into a clean 50 ml beaker. Read and record the approximate measurement on the beaker’s scale. Pour the water into a graduated cylinder and record the amount in the cylinder. What conclusions can you draw about the relative accuracy of glassware for measuring liquids?
Step4: Clean and dry all glassware and return it to the proper place for storage.
Procedure 4: Separating a mixture by filtration-Fine particles or particles that settle slowly are often separated from a liquid by filtration.
Step1: Support a funnel on a small ring on your ring stand. Place a beaker below the funnel to collect the filtrate. Adjust the funnel so that the stem of the funnel just touches the inside wall of the beaker (this will help prevent splashing as the capillary action of the water in the filtrate will cause it to run down the inside of the beaker)>
Step 2: Fold a piece of circular filter paper along its diameter, then fold it again to form a quadrant (see figure). Separate the folds of the filter paper with three thicknesses on one side and one on the other, then place the filter paper cone in the funnel. Use your wash bottle to wet the funnel and the filter paper, press the edges of the filter paper firmly against the sides of the funnel. Exception, the filter should not be wet with water if the liquid to be filtered does not mix with water. Why?
Step 3: Obtain about 3-5g of a mixture containing baking soda and flour. Dissolve the solids in about 50ml of water. Filter out the flour by pouring the mixture through the filter, observing the following:
· Insure that the filter paper does not extend above the edge of the funnel
· Do not completely fill the funnel
· Avoid having the mixture run down the outside of the beaker by using a stir rod pressed against the lip of the beaker. The liquid will run down the stir rod and drop off into the funnel.
The flour is left on the filter paper.
Step 4: The baking soda can be recovered from the filtrate by pouring the filtrate into an evaporating dish and evaporating it over a low flame. Support the evaporating dish on a ring stand with a piece of wire gauze over the ring to help spread the heat evenly. Remove the flame as soon as the liquid begins to spatter.
Step 5: Clean all equipment and return it to its proper place for storage.
Analyzing Data:
Collect data from other groups to determine the density of at least 5 pennies from the 1960’s, 1970’s, 1980’s, 1990’s and 2000’s. Analyze your data in graphical format. Determine if the composition of the pennies has changed significantly from 1960 to 2009 and if yes, estimate when that change might have occurred.
How did you know that the composition changed? What do you think the reasons for changing the composition might be?
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HC/CC/TG KHS