Analysis for Ca+2 Content in Water
WARNING
The experimental content of this analysis is a chain of steps.
  1. Making the Calcium Standard
    • weighing calcium carbonate
    • dissolving calcium carbonate
    • transferring to a volumetric flask
    • diluting to volume
  2. Standardizing the EDTA
    • pipetting the standard
    • titrating the standard
  3. Titrating the UNKNOWN
    • pipetting the standard
    • titrating the standard
The accuracy of your final Result will depend on the accuracy of each step.
With very careful work you should introduce an error in each step of less than 1 ppt (parts per thousand).
If these errors are small and random, some will probably cancel out others. In any case you final results will be satisfactory
However, if there is one large error, it will carry through to your results!

Steps 2 as well as Step 3 above carry the highest potential for error. To minimize errors, these measurements are carried out in triplicate or more. In each case, results which deviate greatly from the others can be ignored and the remaining results are averaged. In this way, large errors are eliminated and small random errors cancel out.

Step 1 is different. It is done only once. An error in making the standard, large or small, carries through the remaining work and goes unnoticed.
The most likely source of error in making the calcium standard is in the quantitative transfer to the volumetric flask.

Will such an error make your ppm Ca in the UNKNOWN too high or too low?

HOW MANY STEPS WERE THERE?

This experiment is described as a sequence of 8 steps. But what about each of those steps?

weighing calcium carbonate

  • Level the balance
  • Zero the balance
  • Measure the mass of the container
  • Measure the mass of the container plus calcium carbonate

pipetting

  • Filling the pipet to the mark
  • Emptying the pipet properly
  • Is the pipet greasy or dirty?

titrating

  • Make sure there are no air bubbles in the filled buret
  • Make sure there are no drops hanging from the tip before starting
  • Did you contaminate the EDTA after standardization?
  • Read the initial volume correctly
  • Titrate to the exact end point. Do not over titrate.
  • Read the final volume correctly
  • Is the buret dirty or greasy so as to not give the correct reading?

For a more detailed analysis of the effects of Experimental Errors on
the accuracy of your calcium concentration determination, see........... ERRORS