lab time Your name NOTE: Answer EITHER Question I(A AND B) OR Question 2 (A AND

Question

lab time Your name NOTE: Answer EITHER Question I(A AND B) OR Question 2 (A AND B) depending on which contaminant (NO; or PO) your group decided to test for Water Analysis Part II Pre-Laboratory Assignment (due before lab on Wed., July 18) 1. A. During Part I of the water Analysis series, you prepared a Stock solution of Nitrate ion containing 250.0 mg N/L. In the second part of this experiment, you will use this Stock solution to prepare four Standard solutions to be used to make a calibration plot. As described in the background information for this experiment, the concentration of Nitrogen in these standards should be between 1 and 10 mg N /L. A. Describe HOW you are going to prepare a standard solution which must contain 8.0 mg N/L. Assume you are going to use a 250-mL volumetric flask for this preparation. Be sure to include necessary CALCULATIONS! B. Another one of the standard solutions should have the concentration of 10.0 mg N/L. Show calculations to be used for preparation of 250.0 mL of this solution.

Explanation / Answer

To prepare 8.0mg/L nitrogen solution:

molarity of the solution=(8.0mg/L)*(1g/1000mg)/(14.007g/mol)=5.711*10^-4mol/L [molar mass of N=14.007g/mol]

1 mol of nitrate(NO3-) contains 1mol N

molarity of nitrate in the solution =5.711*10^-4mol/L

concentration of nitrate in the solution (in mg/L)=(5.711*10^-4mol/L)*(molar mass of NO3-)=(5.711*10^-4mol/L)*(62.004g/mol)*(1000mg/L)=35.410mg/L

Weigh 35.410 mg Nitrate ion and transfer it to the volumetric flask using funnel and add distilled water to dissolve it completely ,then add water upto the mark---this makes a solution of 250 ml of 8.0mg/L

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