Measuring lab
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This document describes procedures for measuring various properties including size distribution, mass distribution, concentration, temperature, and volume. The procedures involve carefully measuring samples and recording the measurements and observations. Key steps include choosing a representative sample, using proper measuring tools, accounting for errors and uncertainties, and recording all relevant data. The goal is to obtain large data sets that can be statistically analyzed to evaluate results and understand sources of error.
Measuring lab
- 1. Procedure A: Measuring Size Distribution Introduction: The objective of this procedure is to measure a large sample and obtain a large number of data, so you can statistically process, analyze and evaluate your data. By deciding which leaves to measure and how, you will undoubtedly influence on the quality of your results. This will introduce error and uncertainty in your data, which will allow you to calculate and graph error bars and standard deviation. Procedure: The procedure to obtain length measurements is simple: 1. Decide and choose which leaves to measure, making sure that the sample is representative of the whole plant. That means, don’t choose leaves only from the top or the bottom. 2. Use a ruler to measure the size of a leave. Whether you decide to measure length or width, or both, is irrelevant, but you should be consistent in the way you measure. Each leaf should be measured exactly the same way. 3. Build a table to record your measurements. 4. Record any observations.
- 2. Procedure B: Measuring Mass Distribution: Introduction: The objective of this procedure is to measure a large sample and obtain a large number of data, so you can statistically process, analyze and evaluate your data. By deciding which beans to measure and how, you will undoubtedly influence on the quality of your results. This will introduce error and uncertainty in your data, which will allow you to calculate and graph error bars and standard deviation. Procedure: To measure mass is simple: 1. Turn on the balance and wait for its self-calibration for about a minute. If the number on the scale is not zero, press the re-zero button once. 2. Put a bean on the scale and wait for the reading to stabilize. Record the reading. 3. Remove the bean without pressing on the balance. Wait for the balance to go back to zero by itself before putting on a new bean. 4. Make sure there are no air currents over the balance (if you are near a door, if people walk by or if you move things quickly over the balance) since this will give you wrong readings. 5. Repeat the procedure for 50 beans. 6. Record your measurements and all other observations.
- 3. Procedure C: Measuring Concentration and Preparing Solutions Introduction: The objective of this procedure is to investigate how error can propagate when combining two measurements. Every time we have to measure something, we introduce error to our measurements from different sources. Since the preparation of a solution implies two measurements, mass and volume, we must take into account and calculate the error and uncertainty that both measurements contribute to the total. Another aspect to take into consideration is the calculation of concentration. The concentration of a solution is commonly expressed in moles per liter, mol/l or M. Hence a solution of NaCl 0.7M means that the concentration of NaCl is that of 0.7moles of NaCl per every liter of water. In order to calculate the molarity of a solution, you need to know the number of moles of solute and the total volume of the solution: 1. Use the chemical formula to determine the number of each type of atom present in the compound. Ex.: Na2CO3 2. Multiply the atomic weight (from the periodic table) of each element by the number of atoms of that element present in the compound. Ex.: Na: 2 x 23.0= 46.0 ; C: 1 x 12.0 =12.0 ; O: 3 x 16.0= 48.0 3. Add it all together and put units of grams/mole after the number. Ex.: molar mass = 46.0 + 12.0 + 48.0 = 106.0 g/mol 4. Calculate the number of moles present by dividing the molar mass by the amount of grams of solute. Ex.: Na2CO3: 1.2ggrams will cancel out Na2CO3: 0.011 mol 106.0 g/mol 4. Calculate the number of liters of solution present. Ex.: 0.15l 5. Divide the number of moles of solute by the number of liters of solution. Ex.: Molarity (M) = 0.011 mol = 0.073 mol/l or 0.073M 0.15l Procedure: 1. Using the information and the equations above, calculate the amount of water and the amount of salt (NaCl) you will need to prepare a solution of NaCl 1M. 2. Measure the volume of water carefully and transfer to a plastic cup. 3. Weigh the amount of salt carefully and transfer it to a plastic cup. 4. Repeat the procedure for a solution of NaCl 2M. 5. Record your data, calculations, and all observations.
- 4. Procedure D: Comparing uncertainty and error in measuring mass: Introduction: The objective of this procedure is to compare the degree of uncertainty given by measuring instruments. In this case you will compare the mass of your samples using two types of balances. You will examine and observe how measurements are made to compare the uncertainty and error given by each balance. Procedure: This procedure is very simple, but requires careful and delicate handling. 1. Turn on the electronic balance and wait for its self-calibration for about a minute. If the number on the scale is not zero, press the re-zero button once. 2. Put a sample on the scale and wait for the reading to stabilize. Record the reading. 3. Remove the bean without pressing on the balance. Wait for the balance to go back to zero by itself before putting on a new bean. 4. Make sure there are no air currents over the balance (if you are near a door, if people walk by or if you move things quickly over the balance) since this will give you wrong readings. 5. Repeat for all 10 samples. 6. Record your measurements and all other observations. 7. In the triple beam balance, with the pan empty, move the three sliders on the three beams to their leftmost positions, so that the balance reads zero. If the indicator on the far right is not aligned with the fixed mark, then calibrate the balance by turning the set screw on the left under the pan. 8. Once the balance has been calibrated, place the sample on the pan. 9. Move the 100-gram slider along the beam to the right until the indicator drops below the fixed mark. The notched position immediately to the left of this point indicates the number of hundreds of grams. 10. Now move the 10-gram slider along the beam to the right until the indicator drops below the fixed mark. The notched position immediately to the left of this point indicates the number of tens of grams. 11. The beam in front is not notched; the slider can move anywhere along the beam. The boldface numbers on this beam are grams and the tick marks between the boldface numbers indicate tenths of grams. 12. To find the mass of the object on the pan, simple add the numbers from the three beams. 13. As with a ruler, it is possible to read the front scale to the nearest half tick mark. 14. Repeat for all 10 samples. 15. Record your measurements and all other observations.
- 5. Procedure E: Comparing uncertainty and error measuring temperature: Introduction: The objective of this procedure is to compare different ways to measure temperature. When we measure temperature, error can be introduced by the instrument used and also by the time the instrument needs to become stable with its environment. During this period, we can read the wrong temperature either because the thermometer is not stable or because the reading is not easy to see. In this lab you will compare the temperature change of your samples using two types of thermometers. You will examine and observe how measurements are made to compare the uncertainty and error given by each thermometer. Procedure: This procedure is simple, however it requires careful and delicate handling. The same procedure applies to a glass thermometer and the digital thermometer in the datalogger. 1. In a cup, measure the mass of one or two ice cubes. Write it down. 2. Add 10g of water at room temperature. 3. As soon as you add the water, introduce a thermometer and start the chronometer. 4. After the first minute take the first reading. 5. Take further readings every 30 seconds for 10 minutes. 6. Collect your data in a table and record all your observations.
- 6. Procedure F: Comparing uncertainty and error in measuring volume: Introduction: The objective of this procedure is to compare different ways to measure volume. When we measure volume,error can be introduced by the instrument used, either by the uncertainty of the instrument or by misreading the marks. In this lab you will compare the volume of your samples using different types of glassware. You will examine and observe how measurements are made to compare the uncertainty and error given by each measuring device. One aspect to keep in mind is the residual liquid that remains in the glassware. Try to get as much liquid out of the glassware as possible. Procedure: This procedure is simple, but it requires careful and delicate handling of glass material. For all measurements, make sure your eyes are level with the marks, as shown in the picture. 1. Calculate and write down the uncertainty given by each measuring device and its scale. 2. Measure 45ml of water with a beaker and pour it in a plastic cup. 3. Repeat the procedure 4 more times, filling a total of 5 cups placed in a row, so you can compare them. 4. Record your measurements and all other observations. 5. Repeat the procedure using a graduated cylinder. Record your measurements with the appropriate significant figures and all your observations. 6. Repeat the procedure using a burette. This time, you DO NOT need to fill the burette to the zero mark, but it is important that you record the initial volume and the final volume. Before you begin, make sure the tip at the bottom of the burette is filled with liquid. Subtract the final volume from the initial volume to obtain the total volume. Record your measurements and all your observations. 7. In order to compare uncertainties measure 50ml with a beaker. Transfer the liquid to the graduated cylinder and record the volume given by the scale of the cylinder. 8. Make sure you have a little bit of liquid in the burette tip. Record the liquid you already have as initial reading. Once you have measured with the cylinder, transfer the liquid to the burette and record the final reading. Subtract the readings to find the total volume. Record all your observations.
- 7. Procedure G: Comparing uncertainty and error in measuring length: Introduction: The objective of this procedure is to compare different ways to measure length. When we measure length, error can be introduced by the instrument used, either by the uncertainty of the instrument or by misreading the marks. In this lab you will compare the length of your samples using different types of devices: a tape meter, a ruler and a caliper. You will examine and observe how measurements are made to compare the uncertainty and error given by each measuring device. Procedure: This procedure is simple, but it requires careful and delicate handling. Make all your measurements on the tabletop. There is no need to lift your samples or the instruments. 1. Using the ruler, measure the length of a bean. Repeat the procedure for 10 samples. Record your measurements and all observations. 2. Repeat the procedure using a tape meter. Measure the beans in the same order you measured them with a ruler. 3. Repeat the procedure using the caliper as shown below: a. Close the jaws lightly on the bean. Be sure the axis of the bean is perpendicular to the caliper. b. Read the centimeter mark on the fixed scale to the left of the zero- mark on the scale. c. Find the millimeter mark on the fixed scale that is just to the left of the zero-mark on the scale. d. Look along the ten marks on the mobile vernier scale and the millimeter marks on the adjacent fixed scale, until you find the two that most nearly line up. e. To get the correct reading, simply add this found digit to your previous reading.