AssignmentSeven - 2 O 2 . Upon heating, the following...

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Take-Home Assignment #7 Please turn in neatly worked solutions for the following problems. Turn in your answers by Wednesday, October 10 th . 1. Solutions of perchloric acid, HClO 4 , may be standardized by titrating against a primary standard of sodium carbonate, Na 2 CO 3 . Typically, the titration is carried out to the carbonate ion’s second endpoint. Suggest a mass of Na 2 CO 3 to use if you are standardizing a solution of HClO 4 whose concentration is within the range of 0.145 M to 0.155 M and you wish to use between 35 mL and 45 mL of titrant. 2. A 50.00–mL sample of white grape juice requires 21.48 mL of 0.03776 M NaOH to achieve a visual endpoint. Express the acidity of the grape juice as grams of tartaric acid, H 2 C 4 H 4 O 6 , per 100 mL. Assume that both of tartaric acid’s acidic protons are titrated at the titration’s endpoint. 3. The formaldehyde, HCHO, content of a pesticide preparation was determined by weighing 0.3124 g of the liquid sample into a flask containing 50.0 mL of 0.0996 M NaOH and 50 mL of 3% H
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Unformatted text preview: 2 O 2 . Upon heating, the following reaction takes place: OH – + HCHO + H 2 O 2 → HCOO – + 2H 2 O After cooling, the excess NaOH was titrated with 23.3 mL of 0.05252 M H 2 SO 4 . Calculate the % w/w HCHO in the sample of pesticide. 4. Suggest an appropriate molarity of HCl if you wish to titrate 25-mL samples of nominally 0.055 M Na 3 PO 4 to the bromocresol green endpoint using between 25 mL and 35 mL of titrant. 5. The alkalinity of natural waters is assumed to arise from a combination of NaOH, Na 2 CO 3 , and NaHCO 3 . Possible combinations include NaOH alone, NaOH and Na 2 CO 3 , Na 2 CO 3 alone, Na 2 CO 3 and NaHCO 3 , or NaHCO 3 alone. Suppose you titrate a 25.00-mL sample of water with 0.1202 M HCl and find that it takes 29.64 mL to titrate to the phenolphthalein endpoint and 34.62 mL to titrate to the bromocresol green endpoint. What compound(s) is (are) responsible for the sample’s alkalinity and what is (are) its (there) concentration(s)?...
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This note was uploaded on 04/02/2012 for the course CHEMISTRY 222 taught by Professor Mcdonald during the Fall '11 term at University of Illinois, Urbana Champaign.

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