1.Compound 1 has a composition of 46.7mass% of element A and 53.3 mass% of element B. A and B also form a second binary compound(compound 2). If the compositions of the two compounds are consistent with the law of multiple proportions, which of the following compositions compositions could be that of compound 2? A)23.4 mass %A 76.6 mass %B B)30.4 mass %A 69.6 mass %B C)33.3 mass %A 66.7 mass %B D)53.3 mass %A 46.7 mass %B E)73.3 mass %A 26.7 mass %B 答案：(B) 2.The amount of calcium present in milk can be determined by adding oxalate to a sample and measuring the mass of calcium oxalate precipitated. What is the mass percent of calcium if 0.429g of calcium oxalate forms in a 125-g sample of milk when excess aqueous sodium oxalate is added? Na2C2O4(aq)+ Ca2+ (aq)→CaC2O4(s)+2Na+(aq) A) 0.107% B) 0.202% C) 0.343% D) 1.10 % E) 1.37 % 答案：(A) 3.Mineral oil can be used in place of mercury in manometers when small pressure changes are to be measured. When is the pressure of an oxygen sample in mm of mineral oil if its pressure is 28.5 mmHg?(d of mineral oil =0.88 g/mL, d of Hg=13.5g/mL) A)1.9 mm mineral oil B)15 mm mineral oil C)32 mm mineral oil D)380 mm mineral oil E)440 mm mineral oil 答案：(E) 不好意思 这三题= = 我看完题目就不知道该怎麽下手做 ...这样 不知道可否请大家指点一下 谢谢~ --

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