Experiment2 Lab Report ZZ - Experiment 2 Precision and Accuracy of Measurements II Data and Results A Balance Use When is a gram a gram Mass Sweetner

Experiment2 Lab Report ZZ - Experiment 2 Precision and...

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Experiment 2: Precision and Accuracy of Measurements
II . Data and Results A. Balance Use: When is a gram, a gram? Table 1. Mass of five packets of sweetener weighed on one balance, % error from true value Step A-2 Packet # Mass Packet + Contents (g) Mass Contents, Calculated (g) % error Contents 1 1.264 2 1.272 3 1.239 4 1.240 5 1.190 Average Standard Deviation Table 2. Mass of one packet of sweetener weighed on five balances; % error from true value Step A-3 Balance # Mass Packet + Contents (g) Mass Contents, Calculated (g) % error Contents 3 1.258 4 1.257 5 1.255 6 1.257 2 1.259 Average Standard Deviation B. Measuring Liquids Mass Sweetner, Nominal (g) 1.0g Mass Empty Packet (g) .211g Balance # , Used in step A-2 True Mass =Nominal Mass =1.0g
Table 3. Precision of 25 mL, 100 mL, and 1L Graduated Cylinders Cylinder Size (mL) Smallest Graduation (mL) Estimated Precision ( ± ml) 25 .2 mL (+/-) .1 mL 100 .2 mL (+/-) .1 mL 1000 10 mL (+/-) 1 mL B. 2. Delivering liquid with various glassware C. Serial Dilutions: Making Solutions with Known Concentrations Kool-Aid Color: Blue Mass of Kool-Aid Used (g): .101g Table 5. Mass of 10 mL of Water Deliverd by a 10 mL Serological Pipet Vol. water (ml) Mass Beaker + Water (g) Mass Water, per 10 ml aliquot (g) Vol. calculated, per 10 ml (ml) 0 63.071 10 72.918 20 82.743 30 92.666 Average Standard Deviation Table 6. Mass of 10 ml of Water Delivered by a 10 mL Volumetric Pipet Vol. water (ml) Mass Beaker + Water (g) Mass Water, per 10 ml aliquot (g) Vol. calculated, per 10 ml (ml) 0 63.071 10 73.061 20 83.044 30 93.033 Average Standard Deviation
Table 7. Absorbance Measurements for Diluted Kool-Aid Solutions Test Tube Volume of Kool- Aid Stock Volume Water Absorbance 1 1 4 .108 2 2 3 .201 3 3 2 .295 4 4 1 .410 5 5 0 .491 Sample Calculations 1. Concentration of Koolaid solution made in 100 mL volumetric flask 2. 1 x 10 -3 M = x mols / .1 L mols= (1 x 10 -4 M) x (1 x 10 4 g)/(1 mol) = 1 g 1.006 g x (1n /1x10 4 ) = 1.006x10 -4 /.10000L = 1.006x10 -3 M 3. Concentration of solution in test tube 1: 1 1 2 2 C V C V = 10 mL x 1.006x10 -3 M=C 2 x 100mL C 2 = 1.006 x 10 -4 M Kool-Aid Color Transmitted _________________ Color Absorbed __________________ λ max, absorbed (nm) _______
III. DISCUSSION Part A. Discussion The manufacturer achieved precision and accuracy in putting 1.0 grams of sugar in each sugar packet, because the mass of sugar within each sugar packet was within the range of .999- 1.060, averaging to 1.0238, and having a standard deviation of .025352. The manufacturer achieved accuracy in obtaining 1.0 gram of sugar in each packet for the most part, with the mass of sugar in each packet having percent errors of 3.1% or below and staying with in ± .5 of 1.0 grams. For only one mass was the percent error 6%, which was not accurate to the manufacturer’s description of 1.0 grams. If the manufacturer had stated each packet contained 1.000 grams of sugar then the measured masses of sugar would still be precise, because the standard deviation is .025352, or approximately ± .03 of the mean mass, 1.0238 grams. However, most of the measurements (1.029,1.031, and 1.060 grams) would not be accurate because they would deviate out of ± .001 of 1.000 grams.

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