题目内容

（2009?湛江模拟）2008年北京奥运会主体育场的外形好似“鸟巢”（The Bird Nest），有一类物质也好似鸟巢，如化学式是B5H9的五硼烷（如图）．下列有关五硼烷的说法错误的是（ ）
【答案】分析：A、根据化学式某元素右下角的数字为该元素原子个数，进行分析解答；
B、根据相对分子的质量为组成分子的各原子的相对原子质量之和，进行分析解答；
C、根据化合物中各元素质量比=各元素的相对原子质量×原子个数之比进行分析解答；
D、根据化合物的概念进行分析解答．
解答：解：A、根据化学式某元素右下角的数字为该分子中该元素原子个数，因此每个B5H9分子中含有5个硼原子和9个氢原子构成，故A不正确；
B、五硼烷的相对分子质量=11×5+1×9=64，故B正确；
C、五硼烷中硼元素和氢元素的质量比=（11×5）：（1×9）=55：9，故C不正确；
D、化合物是由两种或两种以上的元素组成的纯净物，因此五硼烷属于化合物，故D正确．
故选AC．
点评：本题主要考查了对物质的组成和构成的认识，并利用相对分子质量，元素原子个数，元素的质量比进行分析解题．
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