Section Title: (1 point Maximum) (Use the name of the lab) 0 points No Title/Title is illegible or irrelevant. 1 point 2 points 3 points Legible Title relevant to the lab Purpose: (1 point Maximum) No Purpose section (What is the reason for this lab? What Section is illegible concepts will be explored in the lab? What Section does not cover the lab performed hypothesis will be tested?) Legible purpose that answers at least one of the questions: • What is the reason for this lab? What concepts will be explored in the lab? • What hypothesis will be tested? *Note: original data should be included but points will be awarded in the Data Collection and Safe Lab Practices. Theory: (2 points Maximum) • Define of key term(s) • Explain Key Concept(s) • Include chemical or mathematical equations (when applicable) No Theory Section Section is illegible Section does not define key terms, explain key concepts, include chemical or mathematical equations (if applicable) Theory section present and legible Section includes some but not all of the following: • Definitions of key term(s) • Explanations of Key Concept(s) • Includes chemical or mathematical equations (when applicable) Theory section is present and entirely legible Section includes all of the following: • Definitions of key term(s) • Explanations of Key Concept(s) • Includes chemical or mathematical equations (when applicable) Calculations/Graphs: (2 points Maximum) Show any work needed for calculations Show any graphs (if needed) No Calculations/Graph Section Section is illegible Section is missing key calculations or graphs Calculations/Graphs section is present, legible, and includes some but not all of the following: • Calculations shown (including units) • If applicable, graphs is shown and includes title, axis labels, and fit lines (if needed) Calculations/Graphs section is present and entirely legible Section includes all of the following: • Calculations shown (including units) • If applicable, graphs is shown and includes title, axis labels, and fit lines (if needed) Results: (3 points Maximum) No Results Section Briefly describe and summarize the results Section is illegible of the lab Results section is present and mostly legible Section is missing key results Results section is present and legible Results section is present and mostly Sections summarizes and describes some legible but not all of the results Sections summarizes and describes all of the results Conclusions: (3 points Maximum) Includes any reference values and their source Discusses the accuracy of the results Discusses the precision of the data Discusses possible sources of error and what steps to take in the next experiment to minimize them No Conclusions Section Section is illegible Conclusions section is present, mostly legible, but is missing most of the following: • Reference values • Discussion of accuracy • Discussion of precision • Discusses possible sources of error and what steps to take in the next experiment to minimize them Conclusions section is present, legible, but includes some but not all of the following: • Reference values • Discussion of accuracy • Discussion of precision • Discusses possible sources of error and what steps to take in the next experiment to minimize them Post Lab Questions: (3 points Maximum) No Post Lab Questions are answered Section is illegible Post Lab Questions are answered but no work is shown Questions are answered, work shown, but Questions are answered, work is shown, some incorrect answers. and all answers correct Conclusions section is present, legible, and includes all of the following: • Reference values • Discussion of accuracy • Discussion of precision • Discusses possible sources of error and what steps to take in the next experiment to minimize them Density and Treatment of Data Background Density is a physical property of matter. What this means is that every pure substance has a characteristic density at a given temperature. In other words, density can be used to identify a substance. One is able to determine the density of a substance by determining its mass and volume. Since density is a temperature dependent parameter, the resulting density is reported at the temperature at which it was determined. In this exercise you will accurately determine the volume delivered by a 10-mL volumetric pipet; that is you will calibrate a 10-mL volumetric pipette. Typically the volume delivered by a volumetric pipette is etched on the the glass along with the temperarture. However, in practice one should never assume that the volume contained or even delivered by volumetric glassware is exactly that which is indicated by the etching on the glass. Proper calibration avoids the introduction of systematic errors in your measurements. Calibration is performed by first weighing the mass of water delivered by the pipet. The volume delivered is obtained by comparing the mass of water to its density. Remember to measure the temperature of the water so that you use the correct density in your analysis. It is proper laboratory practice to report the accuracy and precision of ones experimental data. Accuracy refers to how close a given measurement comes to the true value (i.e. the Theoretical value). Precision, on the other hand, is a measure of the reproducibility of a given measurement. That is, when an experiment is repeated, precision tells us how close a measurement comes to another measurement. Precision is determined by a statistical method named standard deviation In this experiment you will repeat several measurements in order to generate data such that you are able to statistically analyze your results. Note that reporting results without specifying the precision is meaninless since one does not provide information pertaining to the reproducibility of the experiment. For example, suppose the density of a given metal was determined to be 8.95 g/mL +0.21 g/mL. The value, +0.21 g/mL, tells us the precision of the density resported. The precision in the latter case tells us that the density of the metal is between 9.16 g/mL and 8.74 g/mL. The lower the standard deviation the better the agreement is between subsequent measurements. Name: 1. The density of water at 21.0 °C is 997.9950 kg/mº. Using dimensional analysis express this density in units of grams per milliliter. Be sure to show your work throughout. 1 kg = 1000g 1,0 m3= 1000,000 ML 997.0950 kg 1000g X Х 1.0kg ( . 1000,ooomL - 1.00 m) 70.987995/ mL 0.9989/ mL density at 21.0 °C = 2. Using the data illustrated in the figure below. Determine the density of the metal cylinder. Be sure to show all your work including proper units throughout. Report your response with the correct number of significant figures. close-up view mL close-up view ml 80 80 meniscus 60 70- 70 60 60 60 50 50 50 metal cylinder 30 20 10 metal cylinder 33.625 g top loading balance 33.6259 56 mL-52mL 33.6259 4 MLL =8.5 glme density of metal cylinder 8 g/mL 2 Experimental Procedure 1. Determining the density of a metal (a) Obtain a metal slug and record the unknown number in your laboratory notebook. (b) Use the analytical balance to determine the mass of the dry metal slug. (c) Half-fill a 50-mL or 100-ml graduated cylinder with tap water and record its volume to the nearest 0.1 mL. (d) To avoid splattering tie the metal slug with a nylon string and carefully drop it into the 50-ml (or 100-mL). (e) Roll the metal slug around in the graduated cylinder to remove any air bubbles. (f) Take the difference between the two water levels for the volume of the unknown solid. (g) Repeat the procedure two more times using the same dry mass of the metal cylinder recorded before. 2. Calibration of Pipette (a) Use the analytical balance to weigh a clean and dry 50-mL Erlenmeyer flask with a stopper. Weigh the flask and stopper to +0.001g. To avoid contamination handle the flask with a paper towel or crucible tongs. (b) Pipette 10-mL of deionized water into the weighed flask/stopper. (c) Weigh the flask and its content to 0.0001 g. (d) Using the addition method, repeat this procedure two more times. In addition method, subtract the previous mass reading to obtain the mass of water for each trial. (e) Determine the temperature of the water to 0.1°C and look up the appropriate density (the density is found in the CRC Handbook). Record the density and calculate the volume of water corresponding to one of aliquot of water delivered by the 10-ml pipet (the term aliquot refers to a sample taken for analysis). Question: Is the volume of the pipette really 10-mL? 3
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