在化学中考及竞赛中,经常会出现有关化学式计算的具有一定难度的题,这些题往往成为同学们答题的“拦路虎”。下面结合具体实例介绍几种对付这一“拦路虎”的方法。一、观察法例1已知由CuS、CuSO3、CuSO4组成的混合物中,硫元素的质量分数为x,则混合物中氧元素的质量分数为()。A. In the chemistry exams and competitions, there are often questions about the calculation of chemical formulas that have a certain degree of difficulty. These questions often serve as a “stumbling block” for students’ answers. Here are some ways to deal with this “stumbling block” with specific examples. I. Observing Example 1 In a known mixture of CuS, CuSO3, and CuSO4, the mass fraction of sulfur is x, and the mass fraction of oxygen in the mixture is (). A.