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.
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.
Will be high
d. would be lower morality calculated of permanganate than actual molarity
a) If some sodium oxalate was spilled after it had been weighed out on the analytical balance, the calculated molarity of potassium permanganate would be lower than the actual molarity. This is because the spilled sodium oxalate would result in a lower mass of the substance, leading to a lower number of moles being used in the calculation of the molarity.
To avoid this error, it is important to handle substances carefully and ensure that none of it is lost during the weighing process. One way to do this is by using weighing boats or weighing paper to transfer the substance, minimizing the chances of spillage.
b) If the pipet has not been rinsed with the standard sodium oxalate solution before its use, the calculated molarity of potassium permanganate would be higher than the actual molarity. This is because remnants of previous solutions in the pipet could mix with the potassium permanganate solution and increase the total volume of the solution used in the titration, resulting in a higher calculated molarity.
To avoid this error, it is important to properly rinse the pipet with the solution being used in the titration before taking the desired volume. This involves aspirating the solution into the pipet and then releasing it, repeating the process several times to ensure proper rinsing.
c) If the Erlenmeyer flask was rinsed with the sodium oxalate instead of deionized water before the 25.00 mL solution was measured into it, the calculated molarity of potassium permanganate would be lower than the actual molarity. This is because any sodium oxalate residue remaining in the flask would mix with the potassium permanganate solution and increase the total volume of the solution used in the titration, resulting in a lower calculated molarity.
To avoid this error, it is important to rinse any glassware with the appropriate solvent, usually deionized water, before using them in a titration. This helps ensure that there are no contaminants or residues that could affect the accuracy of the titration results.
d) If the endpoints were repeatedly overshot, the calculated molarity of potassium permanganate would be higher than the actual molarity. This is because overshooting the endpoint means adding excess potassium permanganate solution to the titration, resulting in an increased volume of the solution being titrated. As a result, the calculated molarity would be higher than the actual molarity.
To avoid this error, it is important to carefully and slowly add the potassium permanganate solution drop by drop near the endpoint to avoid overshooting it. Additionally, ensuring that the solution is mixed well before each drop is added can help identify the endpoint more accurately. Regular practice and experience can also improve endpoint determination skills.