题目内容

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，该物质是由、组成的，原子个数比是，摩尔质量为，1摩尔的五硼烷中含约个氢原子．

硼元素氢元素 5：9 64g/mol 5.42x10²⁴
分析：根据五硼烷的化学式为B₅H₉可知五硼烷的元素组成，化学式中元素符号右下角的数字表示该元素的原子个数，据此可计算出分子中原子的个数比，并依据摩尔质量的概念，根据化学式进行计算．
解答：由五硼烷的化学式B₅H₉可知五硼烷由硼元素和氢元素组成，每个分子中含5个硼原子，9个氢原子，所以原子个数比是5：9；单位物质的量的物质所具有的质量，称为摩尔质量，在数值上等于该物质的相对原子质量或相对分子质量，由五硼烷的化学式可知，它的相对分子质量为：=11×5+1×9=64，故其摩尔质量是64g/mol；科学上把含有6.02×10²³个微粒的集体作为一个单位，叫摩尔，1mol五硼烷分子中约含有的氢原子个数为：9×6.02×10²³=5.42x10²⁴．
故答案为：
硼元素、氢元素； 5：9； 64g/mol； 5.42x10²⁴
点评：理解物质由元素组成，分子由原子构成，对摩尔质量概念的了解和运用化学式进行计算的能力是本题的主要考查点，掌握相关知识是解答的关键．

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