Homework Help: Chemistry

Posted by 4B on Thursday, December 1, 2011 at 1:35am.

Explain how the calculated molarity of the potassium permanganate would be affected by each of the following experimental errors. In each case, you must also state if the calculated molarity is higher or lower than the actual morality.
a) Some sodium oxalate was spilled after it had been weighed out on the analytical balance.

b) Prior to its use, the pipet has not been rinsed with the standard sodium oxalate solution.

c) The Erlenmeyer flask was rinsed with the sodium oxalate instead of deionized water before the 25.00 mL solution was measured into it.

d) The endpoints were repeatedly overshot.

Chemistry - DrBob222, Thursday, December 1, 2011 at 6:08pm
5C2O4^2- + 2MnO4^- ....>2Mn^2+ + 10 CO2 and this ignores the H^+, H2O, etc.

Let's look at how M of the MnO4^- is calculated.
1. Weigh Na2C2O4. moles Na2C2O4 = grams/molar mass

2. Place Na2C2O4 in flask, add whatever, titrate with KMnO4.

3. M KMnO4 = moles KMnO4/L KMnO4.

a)If we trash part of the oxalate, it means we will use less KMnO4 in the titration, and a smaller number in denominator of step 3 means M too high.

b. If these are the same kind of pipets I've used for years, they are calibrated TD whatever amount (TD stands for to deliver) and if it delivers the amount it should then the results will not be affected. You may want to check on this yourself since your pipet may not have been a TD pipet.

c. So the Erlenmeyer flask contained too much Na2C2O4 which means the KMnO4 will be too much and the results will be high because of a higher number in the denominator of step 3.

d. You see how it's done. I'll leave this one for you.

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