Suppose the student performing the standardization in part a, above, washed his/

Question

Suppose the student performing the standardization in part a, above, washed his/her buret as per step 2 of the procedure, but neglected to rinse the buret with EDTA before titrating. How will this oversight impact the calculated molarity of the EDTA? Circle one of the following then explain your reasoning below. The calculated molarity will be b. a) artificially low. b) artificially high. c) unaffected by the oversight. Explanation: c. Suppose the student performing the standardization titration squirted some D.I. water into the flask containing the 20.00 mL of the standard Ca solution. How will the addition of D.I. water impact the calculated molarity of the EDTA? Circle one of the following then explain your reasoning below. The calculated molarity will be a) artificially low. b) artificially high. c) unaffected by the oversight. Explanation: Lab 7- Page 7 of7 Green River Community College

Explanation / Answer

Ans. #b. The burette must be first rinsed with distilled water to remove any contaminant present in it. Then, it shall be rinsed with the same solution to be used to titrate the sample, in this case EDTA. This rinsing removes the traces of water present in burette in first step.

If the burette is rinsed with distilled water alone but not with EDTA thereafter, the resultant concentration of titrant EDTA in burette would be lower than the actual value due to mixing of traces of water present at the walls of burette.

Due to dilution of EDTA solution in burette, the calculated molarity of EDTA solution would be lower than the actual value.

So, correct option is- a. artificially low

#c. During titration, 1 mol Ca2+ reacts with 1 mol EDTA4-.

Since addition of water does not affect the number of moles of Ca2+ taken in the flask (though concertation is lowered), the endpoint remains unaffected.

For example, say there are 0.05 moles of Ca2+ in flask. If you added 10.0 mL water to the flask, the [Ca2+] is lowered. However, the addition of 10.0 mL water does not increase or decrease the 0.05 moles of Ca2+ initially present in the flask.

So, correct option is – c. unaffected by the oversight.

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