After completing my experiments with a 50 mL beaker, 50 mLgraduated cylinder, an

Question

After completing my experiments with a 50 mL beaker, 50 mLgraduated cylinder, and a 10 mL pipet Volume determination 50 mL beaker and fill half full withdistilled water. Measured water at 22 degree C and placed the 50 mLbeaker on scale = 29.916 g, tared its mass and added 30 mL ofH2O 57.280 g discarded water and placed beaker onbalance repeated experiment twice more.  Question: If my mass of H2O is 57.280, Trial 2 is 59.176 g andTrial 3 is 58.110 g my calculated volumes are 27.364 mL, 29.98 mL,and 28.914 mL respectfully, how do I get the volumeerror?  Subtracted 57.280-27-362 =29.916 mL isn't this too big? Or, is it a matte ofmoving the decimal place to read 2.99 and rounded to3.00? Furthermore, the calculated results: averagevolume error and range of volume error, can you explain thisconcept? Thank you kinly for any input in solving. Havea nice day. Sincerely, Jeannette After completing my experiments with a 50 mL beaker, 50 mLgraduated cylinder, and a 10 mL pipet Volume determination 50 mL beaker and fill half full withdistilled water. Measured water at 22 degree C and placed the 50 mLbeaker on scale = 29.916 g, tared its mass and added 30 mL ofH2O 57.280 g discarded water and placed beaker onbalance repeated experiment twice more.  Question: If my mass of H2O is 57.280, Trial 2 is 59.176 g andTrial 3 is 58.110 g my calculated volumes are 27.364 mL, 29.98 mL,and 28.914 mL respectfully, how do I get the volumeerror?  Subtracted 57.280-27-362 =29.916 mL isn't this too big? Or, is it a matte ofmoving the decimal place to read 2.99 and rounded to3.00? Furthermore, the calculated results: averagevolume error and range of volume error, can you explain thisconcept? Thank you kinly for any input in solving. Havea nice day. Sincerely, Jeannette

Explanation / Answer

Different texts and professors use volume error in differentways. The way that we'd go about it in my Gen Chem 2 course isfinding the average of the three volumes first and then computingthe standard deviation of them as well. To do such i'd suggestusing the excel functions Average() and STDEV(). Then bymultiplying the STDEV by a .95 confidence interval (functionCONFIDENCE(.05,avg,STD)) you'd find the error as either plus orminus. To find the total error just multiply your answer by two andyou would thus have an error range for volume. So you need to compute the three errors, find the avg, andthen find the range. The range of volume error is simply theaverage +- the error range before you multiply by two. BTW I think your adding the tared mass of the beaker into yourexperiment some how... you should use the mass of water found aftertaring the beaker and the density of water to find volume. It'smore precise. I hope this helps =].

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