QA1_Lab_-_Density

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University of Pittsburgh *

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0120

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Chemistry

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Jan 9, 2024

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docx

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Uploaded by ElderFireGrasshopper32

Quarterly Lab Assessment – Measurement During this laboratory assessment, you will be asked to calculate the mass of a block of plastic without actually weighing the block. Successful completion of this challenge will depend on your ability to take accurate and precise measurements, to apply rules for significant figures in calculations, and to appropriately use the dimensional analysis problem solving method. Part of your grade is based on the accuracy of your calculated mass.  Materials o Metric ruler o Block of unknown mass o Calculator  From your teacher, obtain a block of unknown mass. Make sure to record the block number and color.  The known density value for each different type of block is shown in the table. You will be using these density values to calculate the mass of your block in grams. Color of Block Density (mg/cL) White 5.41 x 10 3 Black 9.85 x 10 3 Milky-White 9.08 x 10 3 Clear 1.18 x 10 4 Gray 1.42 x 10 4  Discuss with your partner what data you will need to collect in order to accurately calculate the mass of the block. Collect all required data, and use it to determine the mass of the block in grams .  After predicting the mass of the block, bring the block to your teacher who will measure its actual mass using a laboratory balance.  Determine the accuracy of your predicted mass by calculating a percent error in order to compare the calculated (predicted) mass with the actual (measured) mass.  With your partner, complete a formal laboratory report for this assessment. Your report should include the four sections listed below. o Purpose – What is the goal of this experiment? What are you trying to find? How? Clearly state the purpose in one or two complete sentences.  The goal of the lab was to find the mass, of the block given to us, in grams. o Procedure – Clear, numbered list of steps (3-5) necessary to calculate the weight of the block. Use complete sentences. Make sure that another student who is unfamiliar with chemistry would be able to follow your procedure. Not what is written above.  Measure height length and width of the block  Find volume using measurements  Use density (given) and volume to find mass (D*V=M)  Convert mass into grams. o Data – A table that includes number and color of your block , all measurements , the results of all calculations , the actual mass of the block and percent error . Units must be included!  Milky white block #4  Height - 2.0 cm  Width - 4.8 cm  Length - 5.8 cm  Actual mass= 63.45g  Experimental value= 50.58g  % error = 20.28%

o Calculations – – Remember to title all calculations and to use the correct format and correct significant figures . You should only need 3 calculations including percent error! Show how to calculate the mass of your block in grams by using the factor-label method.  Calculated volume (L*W*H) – 55.7 cm^3  Converted cm^3 to cL – 5.57 cL  Multiplied (V*D) to find mass - 50575.6mg  Convert mg to g – 50.58g o Conclusion – In the conclusion section, you should do the following:  State your experimental mass value. Describe the accuracy of your results by stating percent error.  State whether your predicted mass was too high or too low.  Discuss at least one valid source of error that occurred during the data collection process. Directly connect the error to your experimental results by clearly explaining your calculated mass was too high or low.  The experimental value (50.58g) of the milky white block #4’s mass was 20.28% off of the actual values (63.45g). The experimental value was too low. One source of error was probably the lack of dimensional analysis. If we used dimensional analysis the % error could’ve been reduced, and we would have had a more accurate mass.

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