Laboratory Assignment: Using a Top Loading Balance 1. How is the balance turned on? To turn on the top loading balance, press down on the bar that is on the front of the machine. 2. Write a complete and accurate procedure for weighing a chemical on the top loading balance. To weigh a chemical using the top loading balance, follow these steps: a. Press the bar on the front of the machine to turn on the balance b. Wait for the digital display to read “0. 00 g” (grams) c. Place a weighing paper on the pan of the balance . Zero out the scale by pressing the bar on the front of the machine e. Using the paper to hold the substance, place the solid chemical on the pan to be weighed f. Check the display for the mass of the chemical (grams) 3. Identify two things that can go wrong when using the procedure in item 2 above. Using the procedure for the top loading balance listed in #2 may result in inaccuracies or accidents. The top loading balance in general is not the most accurate machine to use when determining the weight of a chemical.
An analytical balance digital display is more accurate than a top loading balance in measuring to more places after the decimal point. Also, chemicals left loose on the weighing paper are subject to temperature, humidity, and air changes in the room. When using the method listed above for the top loading balance, accidents can readily occur that may cause harm to people and property. 4. What is the role of the weighing paper in this procedure? What potential risks might be present if the weighing paper is not used?
The weighing paper is used to protect the pan on the top loading balance from the chemicals being weighed. Chemicals inadvertently left on the pan from a previous measurement may result in not only inaccurate measurements, but these chemicals may have harmful reactions if unplanned contact occurs with each other. 5. What is the mass of the chemical in grams in the above procedure? The mass of the chemical measured in the above procedure is 4. 74 g (grams). 6. Write a complete and accurate procedure for weighing a chemical by difference in a volumetric flask.
To weigh a chemical by difference in a volumetric flask, follow these steps: a. Place the volumetric flask on the pan of the top loading balance. b. Zero the scale by pressing on the bar on the front of the balance. c. Transfer the chemical into the volumetric flask using a powder funnel and the appropriate tools to remove the chemical from the storage container. d. Place the volumetric flask, now holding the desired amount of chemical, onto the scale. e. The mass of the chemical (in grams) in the flask will show on the display on the balance. f.
You are basically to subtract the weight of the beaker with the chemical from the weight of the beaker empty. The difference is the weight of the chemical sample. 7. Why is this procedure more accurate than the previous procedure? Make sure your answer is complete and thorough. The weighing by difference method of measurement is more accurate than the previously described method of weighing directly on the pan using a weighing paper. When using the weighing paper on the pan method, it is impossible to know for certain if the balance readings are accurate.
Inaccuracies can occur due to of lack of proper scale calibration. Using the difference method, it does not matter if the scale calibration is off because the difference between the weight of the empty vessel and the weight of the vessel with the chemical is the actual weight of the sample. In summary, the difference between the two readings is the weight of the chemical. 8. Why is the powder funnel used in this second procedure? What problems would be encountered if the powder funnel is not used?
The powder funnel is used to place chemicals in the volumetric flask to prevent spilling the chemicals. It can be difficult to pour light, powered substances into a container without spilling or loosing some of the material. Not only can an experiment or procedure be invalidated or ruined by inaccurately measured ingredients and materials, spilled chemicals can be harmful or dangerous to people. 9. What is the mass of the chemical in the volumetric flask? The mass of the chemical in the volumetric flask is 4. 73 g (grams).