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Unformatted text preview: . The postlab
exercises will guide you through these calculations. 26 Part II. Determination of Calcium in an Unknown
1. Clean three 125 mL, 250 or 300 mL Erlenmeyer flasks. It is very important that the
flasks be extremely clean and well rinsed with deionized water. Accurately weigh
three samples of your dry unknown into the three Erlenmeyer flasks. The unknown
samples should weigh between 0.150  0.180 grams.
2. Titrate the unknown samples using the same procedure that you used for the
standardization of your EDTA solution. Be sure you have three acceptable trials
before cleaning up. To determine if a trial is acceptable, calculate the percent mass
CaCO3 in the sample for each trial based on your volumes of EDTA and mass of
CaCO3 for each trial and then perform the Q test. Report the average percent by mass
of CaCO3 in your unknown along with both a relative and standard deviation, and a
90% confidence limit. The postlab exercises will guide you through these
calculations.
Cleanup: Rinse all glassware with deionized wa...
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 Spring '07
 Nasiri
 Chemistry

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