Procedure PREPARATION OF STANDARD SEA WATER SOLUTION 1. obtain your sea water sa

Question

Procedure PREPARATION OF STANDARD SEA WATER SOLUTION 1. obtain your sea water sample and note the sample letter. 2. Pipette 50.00 mL of sea water into a 250.0 mL volumetric flask and make up to the mark with deionized water. Mix thoroughly. NOTE: This diluted solution is now your stock seawater solution and will be used for both the combined calcium and magnesium determination and the total cation determination. DETERMINATION OF Ca AND Mg 3. Pipette 25.00 mL of the dilute sea water into a 250 mL Erlenmeyer flask. 4. Add approximately an equal volume of deionized water 5. In the fume hood add 2 mL of the ammonia buffer (pH 10 and 6 drops of Calmagite indicator. 6. Titrate with 0.01000 M EDTA to a pure light blue end point. (The solution will change color from pink to purple then finally to the light blue end point.) Note: The titre of EDTA is equivalent to the total additive calcium and magnesium concentration in the dilute sea water sample. 7. Repeat the titration. If the values are different by more than 0.3 mL do a third titration. Use the average of your two closest values for your calculations. DATA Dilution of sea water mL to mL: Dilution Factor Molarity of EDTA. aa Volume (mL) Volume (mL) Volume (mL) Final burette reading 2.9. 2 26. Initial burette reading 2 -To Volume of EDTA. 26 75 25. u 2 S. So

Explanation / Answer

a) EDTA + NaOH --------> NaEDTA + OH

b) average volume =( 22.8 +21.50+22.40)/3 = 22.23 ml = 0.02223 L

Molarity = 0.09731M

moles = Molarity * volume = 0.02223 * 0.09731 = 0.0021 moles

c) molar ratio is 1:1 , therefore, number of moles of H+ ions = 0.0021 moles

d) number of moles of EDTA = molarity * volume = 0.0100 * (25.50+26.75+25.45)/3 = 0.259 moles

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