※ 引述《ching1247 (水无月 靓)》之铭言： : 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) 对化合物A来说，A：B为 1：1.14 再由倍比定律(law of multiple proportions)：两元素化合成不同化合物时， 若其中一元素重量固定，另一元素重量必成简单整数比 所以化合物B之A：B必为1.14的整数倍 (A) A：B＝1：3.27 (B) A：B＝1：2.28 (C) A：B＝1：2.00 答案选(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) 题目的意思是问 在125克的牛奶样品中(含有Ca2+)，再加入草酸钠溶液後会生成 0.429克的草酸钙沈淀，请问在125克样品中Ca2+所占的重量百分率为何？ 设Ca2+有X克，则X＝0.429/128*40＝0.134克 所求＝0.134/125*100%＝0.107% : 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) 先说 Hg的密度应该是13.6g/mL 不知道是否为发文的笔误 此题是问 mineral oil(矿物油)可用来作为汞在压力计的替代品(其实什麽都可以啦) 国中不是有学过 若以「水」取代「汞」，则760mmHg之汞柱换成水柱高度为10336mm水 有想起来的话就知道这题在问什麽 所求＝28.5*(13.6/0.88)＝440 mm mineral oil -- 1 Taiwan319 台湾 ◎再访319乡 活动结束 微笑不结束 2 lvfied/KuaTsey ● 2 Hsinchu 新竹 ◎ 风城事务 HOTMayDayLove/xie 3 ˇTai-travel 台湾 ◎迎接2006年的台湾自助旅行者版 30 boa/Rhapsody/i --

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