Chapter 27: Q31P (page 769)
Why is sample dropped into the preheated furnace before the oxygen concentration reaches its peak in Figure 27-9?
The reason why the sample is being dropped into the preheated furnace before the oxygen concentration reaches its peak is explained in this problem.
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Statistics of coprecipitation. 17In Experiment 1,200.0mL of solution containing 10.0mg of (from ) were treated with excess solution to precipitate containing some coprecipitated . To find out how much coprecipitated was present, the precipitate was dissolved in 35mL of 98wt% and boiled to liberate , which was removed by bubbling gas through the . The HCI/ stream was passed into a reagent solution that reacted with to give a color that was measured. Ten replicate trials gave values of 7.8,9.8,7.8,7.8,7.8,7.8,13,7,12.7,13.7, and 12.7. Experiment 2 was identical to the first one, except that the mL solution also contained of from ). Ten replicate trials gave 7.8,10,8,8.8,7.8,6.9, 8.8, 15.7 , 12.7 , 13.7and .
(a) Find the mean, standard deviation, and 95% confidence interval for in each experiment.
(b) Is there a significant difference between the two experiments? What does your answer mean?
(c) If there were no coprecipitate, what mass of (FM 233.39) would be expected?
(d) If the coprecipitate is (FM 208.23), what is the average mass of precipitatein Experiment 1. By what percentage is the mass greater than the mass in part (c)?
Marie Curie dissolved 0.091 92 g of RaCl2 and treated it with excess AgNO3to precipitate 0.088 90 g of AgCl. In her time (1900), the atomic mass of Ag was known to be 107.8 and that of Cl
was 35.4. From these values, find the atomic mass of Ra that Marie Curie would have calculated.
The thermogravimetric trace on the next page shows mass loss by upon heating. In the first step, waters of hydration are lost to give ~8.1% mass loss. After a decomposition step,19.2% of the original mass is lost. Finally, the composition stabilizes at above .
(a) Find x in the formula Because the 8.1% mass loss is not accurately defined in the experiment, use the 31.8% total mass loss for your calculation.
(b) Suggest a formula for the material remaining at the 19.2% plateau. Be sure that the charges of all ions in your formula sum to 0 . The cation is .
A mixture weighing 7.290mgcontained only cyclohexane, (FM 84.159), and oxirane, (FM 44.052). When the mixture was analyzed by combustion analysis, 21.999mg of(FM 44.009) were produced. Find the weight percent of oxirane in mixture.
Man in the vat problem.15 Long ago, a workman at a dye factory fell into a vat containing hot, concentrated sulfuric and nitric acids. He dissolved completely! Because nobody witnessed the accident, it was necessary to prove that he fell in so that the manโs wife could collect his insurance money. The man weighed 70 kg, and a human body contains |6.3 parts per thousand (mg/g) phosphorus. The acid in the vat was analyzed for phosphorus to see whether it contained a dissolved human.
(a) The vat containedof liquid, and a 100.0-mL sample was analyzed. If the man did fall into the vat, what is the expected quantity of phosphorus in 100.0 mL?
(b) The 100.0-mL sample was treated with a molybdate reagent that precipitated ammonium phosphomolybdate,This substance was dried atto remove waters of hydration and heated tountil it reached the constant composition, which weighed 0.371 8 g. When a fresh mixture of the same acids (not from the vat) was treated in the same manner, 0.033 1 g ofwas produced. This blank determination gives the amount of phosphorus in the starting reagents. Thethat could have come from the dissolved man is therefore.How much phosphorus was present in the 100.0-mL sample? Is this quantity consistent with a dissolved man?
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