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《我们周围的物质是纯净的吗》Coursera课程内容总结： 本课程主要探讨我们周围物质的纯净度问题。课程指出，我们实际观察到的许多物质并非纯净的，例如土壤或食盐，它们都包含多种不同的组成部分。 **物质的分类：** 根据化学性质，物质可分为两类： 1. **纯净物 (Pure substance):** * 是指由**一种**物质组成的、具有**固定性质**的同质材料。 * 纯净物无法通过**物理方法**分离成其他物质。 * 示例：氧气、硫、铁。 * **注意：**由两种或两种以上不同粒子以**固定比例**结合而成的物质，也被视为纯净物。例如，氯化钠（NaCl）是由钠离子和氯离子以固定比例结合而成，因此是纯净物。其他例子包括氧化镁 (MgO)、二氧化碳、硫酸铜等。 2. **混合物 (Mixture):** * 是指两种或两种以上物质（元素、化合物或两者兼有）以**任意比例**混合而成，且各组分**不发生化学变化**，保留其原有特性的产物。 * 示例：黄铜是铜和锌的混合物。
We know all the matter around is not pure. If we observe some soil (Mitti) and some surge placed on two different sheets of paper with a magnifying glass, we find soil contains clay particles, some grass particles and even some dead insects etc. That is soil particles of different kinds is called an impure substance.Type of matter: -On the basis of chemical nature, matter can be classified into two types:(i) Pure substance. (ii) Impure substance (mixture)(i) Pure substance:- A homogeneous material which contains particles of only one kind has a definite set of properties, is called a pure substance. ORA pure substance is a distinct type of matter that can not be separated into other matter by any physical process eg. oxygen, sulphur, iron etc. are pure substance however, if a substance is composed of two or more different kinds of particles combined together in fixed proportion by weight, then the substance is also regarded as pure substance. e.g. Sodium chloride is a pure substance, because it has a fixed number of sodium and chloride ions, combined together in fixed proportion by weight, Similarly, magnesium oxide (MgO), Carbon dioxide, copper sulphate etc. are pure substance.(ii) Mixture:- When two or more substance (elements, compounds or both) are mixed together in any proportion, such that they do not undergo any chemical change, but retain their individual characteristics, the resulting product is called a mixture. e.g. Brass is mixture of copper and zinc.
