I. Oxalic acid dihydrate, H2C2042H20, is often used as a primary standard for th
ID: 561749 • Letter: I
Question
I. Oxalic acid dihydrate, H2C2042H20, is often used as a primary standard for the standardization of base solutions. For a procedure comparable to this experiment, approximately how many grams of oxalic acid dihydrate should be used in order to have a volume of about 15 mL of NaOH solution (approximately 0.15M) for the titration? The acid is diprotic (two H+ react). Problems 2. How would the observed molarity of your experiment be affected by the following circumstances (i.e would it be higher than the true value, lower than the true value or remain unchanged)? Give your reasons. a) The potassium hydrogen phthalate is dissolved in more than 50 mL of water b) The potassium hydrogen phthalate in the reagent bottle in the laboratory has been left open on a bumid day and the potassium bydrogen phthalate has absorbed some moisture before you removed your sample of the acid e) While swirling the flask during the titration, some of the liquid splashed out before the end point was reached. 3. How would the equivalent weight be affected by the following circumstances (i.e. will it be higher than the true value, lower than the true value or remain unchanged). Give reasons for your answers a) The burette is washed with distilled water but not rinsed with base. b) A small amount of weighed acid was spilled during the transfer from the weighing vial. c) The weighed acid is transferred to a wet Erlenmeyer flask 123Explanation / Answer
1. The oxalic acid dihydrate has molar mass of 126.02 gm.
For 1 L and 1N SOLUtion 61.01 gm of oxalic acid is required.
The required oxalic acid in gms for 15 ml and 0.15 N,
61.01/1000 *15 * 0.15 = 0.137 gm.
2.a. The dissolution in the higher amount of water will lead to the decrease of the strength ie the molarity. The more dilution in general leads to the decrease in conventration.
B. The molecular weight of the oxalic acid will be disturbed. Humidity and moisture actually change the no. Of water of crystallistion and hence the molecular weight will increase. Hence we will need higher amount of oxalic acid for the standarisation. The molarity will be undisturbed as the oxalic acid is a primary standard.
C. Due to the spill the molarity found will be less than the true molarity of the solution.
3a. Rinsing with base actually removes the residual acid that could be present.. The equivalent weight thus have the interference of the residual acid and the value will lowered.
B.the spilling decreases the acid and the equivalent weight calculated will be less.
C.the transfer to the wet erlenmeyer flask will have no effect to the equivalent weight.