Natural Salt Solutions 2: Analysis of Seawater Overview Getting Started Techniques Procedure FAQ Full Lab Manual Introduction & Goals Chemistry & Background Key Questions Prelab Problems Safety Procedure In Your Write-up Appendix Experiments Index ChemLab Home		Prelab Problems 1. Suppose that 1 mmol of each of the following salts is passed through a large cation exchange column in the hydrogen form and all the displaced hydrogen ions are rinsed off and titrated with sodium hydroxide. Predict the number of mmol of base consumed in each case. a) NaBr b) Al2(SO4)3 c) MgAl2(SO4)4 d) Fe(NH4)2(SO4)2 6H2O Recall that NH4+ and SO4-2 are polyatomic ions which exist as a group of atoms with an overall change. Link to FAQ about this problem 2. A KHP sample weighing 0.1960 g is titrated with 0.1246 M NaOH. How many milliliters NaOH would you expect to add to reach the endpoint? The molecular formula of potassium hydrogen pthalate (KHP) is C8H5O4K. You can easily calculate the molecular mass using the molecular mass calculator in the periodic table, elsewhere on the site. Link to FAQ similar to this problem 3. Compare your estimated column capacity from last week to the expected number of cations in your sea water sample. Will your column have adequate capacity for the sample? Link to FAQ about this problem 4. A 2.00 mL sample of seawater is eluted on an ion exchange column. After complete rinsing, the effluent is titrated with standardized 0.1227 M NaOH solution. How many milliliters of NaOH do you expect to add to the flask to reach the endpoint? 5. Four analyses of 2 mL of seawater gave the following results: 0.518 0.531 0.527 and 0.523 equivalents/L Calculate the mean value of the equivalent concentration. Calculate the standard deviation of the mean and the 95% confidence interval. Use the ± value of this confidence interval as an absolute uncertainty and calculate the relative uncertainty in the average result. How does the relative uncertainty compare to the less than 1% expected? How would you report the average result, with a confidence interval?
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