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Lab 1 - C h e m 11 2 4 M e a s u r e m e n t s i n G e n e...

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1 DGC 8/09 Ch e m 1124 M e a s ur e m e nt s in G e n e ral Ch e mi s try PRE-LAB EXERCISES 1. The calibration marks on a 50-mL buret are 0.1 mL. What is the correct buret reading for the liquid in Figure 1? Note that all buret readings should be reported to 2 decimal places. 2. A digital thermometer reads 23.2 º C. What is the implied uncertainty in this measurement? 3. The following data were obtained in the measurement of a metal rod. Use the Rules for Calculating and Reporting the proper number of significant figures as discussed in lecture to report your values requested in thi s qu e s tion and throughout th e e xp e rim e nt . ( You m ay wri t e t h e c al c ula t or valu e , and t h e n m ar k a s ingl e m ar k t hrough i t , r e wri t ing t h e f inal an s w e r b e s id e t h e c al c ula t or valu e . ) Length = 6.73 cm Diameter = 3.22 cm Mass = 149.056 g a. What is the volume (cc or cm 3 for cubic centimeters) of the metal rod? b. What is the density of the metal rod? c. Assuming that the rod is one of the metals whose densities are given in Table 2, what is the most probable identity of the metal? 4. What are the two best ways to ensure that there are no bubbles in the stopcock (or petcock) as in Figure 2? 5. Liz, a student in General Chemistry I, carefully followed Lab Procedure 2 and collected the data in the table below using four different laboratory apparatuses that are used to measure the volume of liquids at 21.3ºC. 1 The mass of deionized water (dH 2 O) dispensed from each apparatus was weighed on the 0.001 g balance. This was repeated for a total of three trials. a) From the data below calculate the following for each apparatus using an excel spreadsheet making sure to use the appropriate number of significant figures. Tape a copy of the spreadsheet into your notebook. i) the average, ii) the standard deviation of the mass of dH 2 O dispensed, iii) the average density of water dispensed, iv) the percent error. b) From Liz’s data w hich apparatus is the most accurate? c) From Liz’s data which apparatus is the most precise? 1 For the density of pure water at various temperatures go to http://www.simetric.co.uk/si_water.htm
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2 DGC 8/09 Ch e m 1124 M e a s ur e m e nt s in G e n e ral Ch e mi s try R e ad t hi s e n t ir e Labora t ory pro ce dur e b e for e st ar t ing t hi s lab . You will work individually on t hi s lab . All da t a i s t o b e r ec ord e d in t h e lab no t e book a s t ak e n during t h e lab . Mat e rial s and Equipm e nt 15-cm Digital Calipers dH 2 O 50-mL Buret, Buret Clamp, Ring Stand Numbered Metal Samples 50 or 100-mL Graduated Cylinder 2-L Polyethylene Pitchers 50 and 150-mL Beaker Digital Balances, 310 g 1 mg 25-mL Pipette Digital Balances, 5.1 kg 10 mg Introdu c tion In today’s lab you will become acquainted with measuring tools that you will continue to use through out the rest of this course in the laboratory. Good s c i e n ce c an only b e don e if t h e prop e r t ool s ar e u s e d c orr ec t ly f or t h e t a s k s a t hand . Because chemistry is a quantitative science, whenever
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