确定化学式的几种方法

1 化学式的确定 1.利用元素间的质量比确定化学式 例1 元素X与元素Y可以组成A、B两种化合物。已知A的化学式为XY,其中X与Y的质量比为3:4。若B的化学式中X与Y的质量比为3:8,则B的化学式为( )。 (A)X_2Y (B)XY_2 (C)XY_3 (D)X_3Y 解:设X、Y的原子量分别为x、y,由A的化学式知x/y=3:4,进而可知在B中X、Y的原子个数比为(3/3):(8/4)=1:2,即B的化学式为     

玩! 乐互动

小测试1、请选择你的爱情果:(1)柚子(2)石榴(3)苹果(4)西瓜(5)柠檬(6)菠萝(7)火龙果(8)樱桃(9)香蕉(10)椰子(只能选择一个哦)2、给你做个测试:你现在想到的第一个异性是谁,再给日字添一笔成为另一个字,现在看答案吧!3、测验:以下几种方便面你最喜欢哪种:(1)鲜虾鱼板面(2)红烧牛肉面(3)香菇炖鸡面(4)梅菜扣肉面(5)番茄牛肉面(6)红烧排骨面     

迎接“1996”——趣题一组

1.计算:①1996 xZ(XX)双幻工g为一2(X X) xl卯619961卯6 ②(l 3 5 l卯6) 1995)一(2 4 6 …… ③击·击·击·2.化简 1995 x 19961乡灭i 1卯52二1望抖xl叨6 3.比较大小: 叫叫叫男卜见959595 系答子井三与彩夭烹兰景兰 95959595 J96?% 4.把1至1996这1卯6个自然数依次写下来得到一个多位数12抖56789101卜·…19951卯6。这个多数位除以9的余数是多少? 5.填上运算符号使等式成立: 6 6 6 6 66 6 6 66二1996 参考答案: 1.①解:原式二1哭巧xZ(X X)xl‘X幻1以X)1一2(X X)xl卯6 x 10[X)1《众)1=00 ②解:原式二1 (3一2) (5一4) ……(l卯5一l卯4…     

课程改革中的数学教学方法谈

数学是一门逻辑推理极强的科学,如果概念上稍有差错和忽视,会使推论出现谬误。所以,要提高数学水平,就必须掌握扎实的数学基础知识。然而,目前在职业教育教学中,我们发现学生存在很多通病。主要原因是基本概念混乱不清,主要表现在如下几个方面:逻辑连结的混乱如:(1)不等式的解为X≥5,大部分学生回答成X>5且X=5。(2)把3>2或2=3判定成假命题。(3)把方程X2-2X-3=0的解书写成X=1且X=3,有的干脆写成X=1X={3。(4)如作业中一道题,已知命题P:X2-4=0的解为X=2,命题q:X2-4=0的解为X=-2,求pvq。不少同学回答成X2-4=0的解为X=2或X=-2,他们把假命…     

2004年广西普通高考录取分数线

一、第一批录取的院校科目组:X1(3+物理、化学组)642分X2(3+化学、生物组)667分X3(3+物理、综合组)626分X4(3+政治、历史组)675分X5(3+历史、地理组)708分X6(3+政治、综合组)656分二、第二批录取的院校科目组:X1(3+物理、化学组)546分X2(3+化学、生物组)571分X3(3+物理、综合组)538分X4(3+政治、历史组)582分X5(3+历史、地理组)655分X6(3+政治、综合组)516分三、第三批录取的院校科目组:X1(3+物理、化学组)523分X2(3+化学、生物组)559分X3(3+物理、综合组)520分X4(3+政治、历史组)559分X5(3+历史、地理组)599分X6(3+政治、综合组)50…     

数学分层优化设计(一)(北师大版 整式的除法,第一章综合)

一、填空题1 .6x“令(一Zx)-2.一as十(一a)2-·(一3·2“·,3二(一告a4oZ)一·(普二2一4了3,2)、(一2二2)-女口果一2以3阴b4与普。6b4·是同类项,那么阴 儿-9x2 mxy 4犷是完全平方式,则m一_一4X2(一1 2￡一专XZ)一—·二、选择题8.下列计算,结果正确的是A .8尹一2扩一4C.(一Zxz夕2)3令(一砂)3=一2x3夕3“·‘。二6令5X3一音X3D·(一xyZ)令(一x,y)-一犷若x爪丫、今二3, 任A .m一6,n一1一4尹则B.m~5,n一1C .m一5,n一0 D.m一6,n一O下列式子运算正确的是(一a4)一(一a)“一a“10A.C.(6 xy3)2一1若(m十5)m 1Zx乙夕tiD·M一m“ 4m一5,那么…     

速算烷烃、芳香烃二卤代物的同分异构体数目

<正>标记说明:(1)所有烃省略氢原子,只写碳骨架;(2)伯碳原子、仲碳原子、叔碳原子、季碳原子分别表示为1°、2°、3°、4°。取代规律:4°不加X (X表示卤素,下同),3°至多加一个X,1°和2°可加两个或一个X。本文将借助图形直观地表示组合方式,如图1所示。(1)同碳上等效碳字母同用数字区别;(2)碳链上对称的等效碳,字母同记"'"区别;(3)类似于坐标系"|"代表组合方式,"□"代表占位,把它们写在对应横行     

“分解因式”解数值计算题

对于有些数值计算的竞赛题,“硬算”是不明智的,而使用因式分解法,往往能为解题找到十分简捷的途径.例1计算(2又5十2)(4只7+2)(6X9+2)(8Xll+2)(IX4一2)(3X6+2)(5X8十2)(7X10+2) (1996解注意到。(。+3)十2一二2+3。+2(1 994XI 997+2)(1 993XI 996+2)‘年北京市数学竞赛题) 一(九+1)(凡+2).这里n一1,2,3,…,1”4,这样原式可化为原式一(3 X4)(5只6)(7 XS)(9 X 10)…(1 995 X 1 996)(2 X3)(4 XS)(6 X7)(8 Xg)一(1 994 X 1 995)1 996998。4一1+ 0︸户1(一9 一z!+瑞+十、、,口了一、l尹4一i(s4一卜代沙一扣4一i+ 日J︸,土一2一r.‘一了…     

数学第八册期末综合练习设计

一、直接得数.①52一13②37火3③28十3705+22一0.02⑤99 X 43225⑧35.刁+6.04 二、填空: 1·求() ⑥255 x 99+255⑨4x 9 x 25⑦25.3叫做乘法。2.15X125又4Xa一(15X4)丫(1 25X8)用了)定律。3.‘把左右两边相等的式子用直线连接起来.99荞325 4X(8 X 1 25)34X(52+66)100X325一3254火8+4X125 34X52+66X344.在O里填上>、<、~。锐角O钝角0.31+0.0100.39一0.10.olxl00OO.ol+10直角十27000周角,·2亿O,20。”万0,,O,击5.把375+(31一16)x xs编成文字题6.100个0.1是()。7.已知:乙l~匕2~34。,乙3二匕月。间匕3艺刁=_度,之2十匕3~_度?8.刁分米二…     

香港中学会考化学试题和答案

(i)写出X.Y和Z的名称。(ii)用方程式解释下列反应的可见现象:(1)把固体加热,(2)H_2S和Y溶液的反应,(3)NaOH溶液与X溶液的反应,(4)NaOH溶液与Z溶液的反应,(5)硝酸酸化的AgNO_3溶液与X溶液的反应,(6)盐酸酸化的BaCl_2溶液与Z溶液的反应。(iii)加氨水于下列溶液时,有什么现象?不需写反应方程式。(1)X溶液,(2)Y溶液,(3)Z溶液,答案:(i)X是NH_4Cl.Y是Pb(NO_3)_2.Z是ZnSO_4     

卡思卡特城堡

It is worthy of noting that, whilst Crookston Castle witnessed the earlier and happier portion of Mary's variegated life,     

不同的吃喝玩乐

一、吃和喝吃苹果 eat an apple, 吃药 take medicine,吃糖 have some sweets,吃饭 have one's meals,吃馆子 dine out,吃惊 be surprised/     

漏洞百出的教育

Many college freshmen arrive woefully unprepared to do college work, and as disadvantaged populations continue to grow, the share of the American work force that has made it through college is expected to plummet. Many experts blame that educational failure not just on high schools but also on colleges. School & College, a special report by The Chronicle, looks at efforts to fix the system. What reforms would better prepare students for college? What should schools and colleges be doing differently? How should state and federal officials help?     

只要努力,不要后悔

There are numbers of crossroads on our long and unpredictable life journey where we totally have no idea about which direction to choose. No matter what our decision is, we should not turn back, but face the music and go ahead instead. I am this kind of girl who always does try without regretting, one example is how I dealt with my love.     

浅谈移民问题

Migration occurs behind a variety of reasons and has a great effect on the whole world. People may migrate in order to improve their economic situation, or in order to escape civil strife, persecution, and environmental disasters. The impact of migration is complex, bringing both benefits anddisadvantages. This paper briefly talks about the causes of migration, the allocation of benefits, and the ways in which individual countries and the international community deal with this important subject.     

Sister Carrie, an Adherent of Desires

Sister Carrie is one of the most controversial characters in American literature.Thought as a "fallen woman" firstly,she was defined as a "new woman" by some critics later. However, by digging into the motivaton behind the whole process of Carrie's "success", the relationship between Carrie and her creator (the author), the social conditions of then American, it can be found that Carrie has never been free-standing on her thought and she has never found her real-sdf even after becoming a famous actress. In a society dominated by mass consumerism Carrie is only an adherent of her own desires. She also is a representative of all those country girls flooded into cities, a symbol and a sacrifice of the urbanization of America in a time countryside was overcome by cities.     

Improvement of one-cycle controller by use of proportional integral differential controller

1.IntroductionOne-cyclecontrolmethod,whichwasproposedaboutonedecadeago[1],hasbecomeanattractivemethodinspecialfieldssuchaspowerfactorcorrection[2-6],switchingamplifiers[7,8],etc.Themainideaofthiscontrollerisbasedonintegrationofdiodevoltageinone-cycleandforcesittobeexactlyequaltothereferencevalue.Themainadvantageofthiscontrollerisitsrealtimeabilitytorejectthevariationofinputvoltage[1].Despitethisgreatability,ithasnogoodperformancesinrejectingofloaddisturbanceandfollowingreferencecommands.Espec…     

库克斯顿城堡

城堡, 是欧洲典型的建筑之一, 每个城堡都有一个美丽的传说或是一段历史。从本期开始, 我们将推出“城堡之旅”, 带各位读者去浏览、观赏欧洲各地的城堡, 开始一段文化与历史的旅途!     

The Reader Response Approach to Teaching of English Literature

During interview with English majors, it was found that a majority of students expressed disappointment with their experience of English literature classes. Students' dislike of learning English literature appears to be the major problem of teaching English literature in China. Reader response approach is a good way to solve this problem. In this paper, I explain the rationale behind the reader response approach, such as its origin, definition, features, assumptions, and strategies. Then I illustrate how reader response approach works as a teaching strategy by presenting several teaching models. At last I evaluate its usefuiness for teachers and present the advantages of reader response approach in Chinese context.