Question

(12 pts.) The principal investigator (PI) for the laboratory you are doing research in has tasked with you to make 100 mL of an aqueous sodium phosphate (Na3PO4) solution with a formal concentration of 10.00 mM. Proceed through the following steps to quantify the concentration and uncertainty for the solution you produce. Note: for molar masses use the following values (Na = 22.98976928(2), P = 30.973762(2), O = 15.9994(4) g/mol) And propagate uncertainty for molar masses of compounds as standard uncertainty as we’ve done in lecture – do NOT divide by a square root of 3 as “older” versions of the Harris textbook presents. Treat them the same as if you have an uncalibrated volumetric flask with standard uncertainty. a. (4 points) Calculate and report the average molar mass (including absolute uncertainty) for sodium phosphate. b. (4 points) The balance you use to mass the sodium phosphate has been recently calibrated and has been found to report masses with a random uncertainty of ± 40 ug. Thus you mass out 1.64007 g of sodium phosphate and add it to a 100 mL volumetric flask. Considering both the uncertainty in the molar mass of the sodium phosphate and the uncertainty in the balance - calculate and report the number of moles (including uncertainty) that you added to the flask. c. (4 points) The volumetric flask you are using is “class b” which is characterized as having a systematic uncertainty of ± 0.2 mL; and you neglected to calibrate this flask. You fill the flask exactly to the 100.0 mL mark, but recall that this is an uncalibrated flask. Considering both the uncertainty in the number of moles of sodium phosphate you added (from the previous question) and the uncertainty in the volume of the flask - calculate and report the molarity (and uncertainty) of this solution

Answer 1

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