Tue July 31, 2012 By:

What is the main diff. between "Law of Definite Prop." & "Law of Multiple Prop.??"

Expert Reply
Wed August 01, 2012

The Law of definite proportions states that a given compound always contains same elements in the same proportion no matter how you make a chemical compound, An example: Whether you make water by combining hydrogen and oxygen or by decomposing hydrogen peroxide, the resulting water will still be 1 part by mass of hydrogen to eight parts by mass of oxygen i.e. 88.8% oxygen to about 11.2% hydrogen by mass.

The law of multiple proportions states that if two elements form more than one compound between them, then the ratios of the masses of the second element which combine with a fixed mass of the first element will be ratios of small whole numbers. This law refers to different chemical compounds that can be formed when two elements react with each other. For example, hydrogen and oxygen can react to form water (H2O) and hydrogen peroxide (H2O2). In the first compound, one gram of hydrogen combines with 8 grams of oxygen. In the second, one gram of hydrogen reacts with 16 grams of oxygen. If we look at the ratio of these to each other, 8/16 =2, which is a whole number. The law of multiple proportions says that whenever oxygen and hydrogen (or any two elements react to form more than one compound), the ratios of the elements to each other will be some whole number multiple of the ratios of the elements in the other compounds.

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