化学式是初中化学的基础,有关化学式的计算在中考中极为常见.下面举例介绍此类问题的几种常用解法,以提高同学们的学习兴趣和解题能力.一、估算法例1 X和Y两种元素可以组成两种化合物XY_2和X_aY_b.XY_2中X元素的质量分数为50%,X_aY_b中X元素的质量分数为40%,则X_aY_b的化学式为().A.XY_3 B.XY C.X_2Y D.X_3Y研析与解答:在XY_2中X与Y的原子个数之比为1:2,X的质量分数为50%.在X_aY_b中X的质量 Chemical formula is the basis of junior high school chemistry, the calculation of the chemical formula is very common in the senior high school entrance examination. Here are some examples of such commonly used method to improve students’ interest in learning and solving problems. The elements can be composed of two compounds XY_2 and X_aY_b.XY_2 X element mass fraction of 50%, X_aY_b X element mass fraction of 40%, then X_aY_b chemical formula () .A.XY_3 B.XY C.X_2Y D.X_3Y Analysis and Solution: The ratio of the number of atoms of X and Y in XY_2 is 1: 2 and the mass fraction of X is 50%. The mass of X in X_aY_b