Test-exam 2

00 1 1 092 1462 5 1482 flask2 2500 1 1 1482 2812 5

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Unformatted text preview: 14.82 28.12 5 28.30 Flask3 25.00 1 1 5.11 18.40 5 18.59 NNBE is Need Not Be Exact. (NNBE) (NNBE) Colorless Pale Yellow Blue Colorless 25 26 Na2S2O3 reacted(mol) 27 [Na2S2O3] (M) 6H+ + 6S2O32- + IO3- I- + 3S4O62- + 3H2O Based on the above spreadsheet, which of the following observations is INCORRECT? a. The volumes of potassium iodate in C16, D16, and E16 should be measured by pipet not graduated cylinder. b. The iodate ion is oxidized by the thiosulfate ion.* c. The sodium thiosulfate is a stronger reducing agent than the potassium iodate. d. The amount of potassium iodate reacted in the three trials should be very close to each other. e. The end point of this titration is detected by the use of freshly prepared starch solution. Buffers & Indicators 6. What is the pH of a 0.1M NaAc (sodium acetate) solution when activity is ignored (Ka for acetic acid, HAc, is 1.75 x 10-5)? a. 3.02 b. 5.11 c. 8.88* d. 10.1 e. 12.2 Ans. NaAc is soluble in water, therefore NaAc Na Ac Na H 2O NR Ac H 2O HAc OH K K w 1.0 1014 5.71 1010 5 K a 1.75 10 4 0.1 – x x 10 x 5.71 10 x2 x...
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This note was uploaded on 03/03/2011 for the course CHEM 100A taught by Professor Dai during the Spring '06 term at UCSD.

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