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What Is Law Of Multiple Proportions, Important Topics For JEE 2025

Law Of Chemical Combination In Chemistry : The Law of Chemical Combination in chemistry encompasses two fundamental principles: the Law of Definite Proportions and the Law of Multiple Proportions. The Law of Definite Proportions states that a chemical compound always contains the same elements in the exact same proportion by mass. The Law of Multiple Proportions asserts that when elements combine in more than one way, the masses of one element that combine with a fixed mass of another are in small, whole number ratios.
authorImageShrivastav 16 May, 2024
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Law Of Chemical Combination

Law Of Chemical Combination : Chemistry can sometimes feel like a complicated puzzle, with elements combining in various ways to form different substances. But at the heart of this complexity lies some fundamental laws that govern how these combinations occur. One such law is the Law of Multiple Proportions, which sheds light on the relationship between different elements in compounds. Let's dive into this law and unravel its significance in the world of chemistry.

What Is The Law Of Multiple Proportions?

  • This law was given by Dalton in 1803.

  • If two elements combine to form more than one compound, then the different masses of one element which combine with a fixed mass of the other element, bear a simple ratio to one another.

Law of Multiple Proportions : The Law of Multiple Proportions is a principle in chemistry that describes the relationship between the masses of elements that combine to form different compounds. Simply put, it states that when two elements can combine to form more than one compound, the masses of one element that combine with a fixed mass of the other element are in ratios of small whole numbers. To understand this law better, let's break it down into simpler terms. Imagine you have two elements, let's call them Element A and Element B. These elements can combine to form different compounds.

Now, according to the Law of Multiple Proportions, if Element A combines with Element B in more than one way to form different compounds, the ratio of their masses in each compound will be a simple whole number ratio.

Law Of Chemical Combination Examples

Nitrogen and oxygen combine to form five oxides, which are: Nitrous oxide (N 2 O), nitric oxide (NO), nitrogen trioxide (N 2 O 3 ), nitrogen tetraoxide (N 2 O 4 ) and nitrogen pentaoxide (N 2 O 5 ).

Weight of oxygen which combine with the fixed weight of nitrogen in these oxides are calculated as follows:
Oxide

N 2 O

NO

N 2 O 3

N 2 O 4

N 2 O 5

Ratio of weight

28:16

14:16

28:48

28:64

28:80

Number of parts by weight of oxygen which combine with 14 parts by weight of nitrogen from the above are 8,16,24,32 and 40 respectively.  Their ratio 1 : 2: 3 : 4 : 5, which is a simple ratio.  Hence, the law is illustrated. Note. ( This law is not applicable in case of isotopes.)

Law Of Chemical Combination Solved Examples

Q.1 : On analysis it was found that the black oxide of copper and the red oxide of copper contain 79.9% and 88.8% metal respectively.  Establish the law of multiple proportions with the help of this data.

Ans. In the back oxide, 79.9 g copper combines with (100–79.9), i.e. 20.1 g oxygen.

  • In red oxide 88.8 g copper will combine with 100–88.8 = 11.2 g

  • According to red oxide 79.9 copper will combine with = 10.08 g oxygen.

Thus the weights of oxygen that combine with the same 79.9 g copper are 20.1 g and 10.08 g respectively. These are in the ratio 20.1 : 10.08 = 2:1

It is a simple whole number ratio.  Hence, the law of multiple proportions is established.

Q2. Carbon forms two oxides.  One contains 27.27% carbon & another contains 42.86% carbon.  Show that the data illustrate the law of multiple proportion.

Sol. The mass ratio of C : O in first oxide = 27.27 : 72:73 = 3:8

The mass ratio of C : O in second oxide = 42.86 : 57.14 = 3:4

Hence for each 3 gm of carbon the masses of oxygen combine is 2:1 ratio.

Hence the data is according the law of multiple proportion.

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Q.1 :  What is the Law of Multiple Proportions?

Ans.    The Law of Multiple Proportions is a principle in chemistry that describes the relationship between the masses of elements that combine to form different compounds. It states that when two elements can combine to form more than one compound, the masses of one element that combine with a fixed mass of the other element are in ratios of small whole numbers.

Q.2 : How does the Law of Multiple Proportions work in real-life examples?

Ans.    An example illustrating the Law of Multiple Proportions involves carbon and oxygen. These elements can combine to form two different compounds: carbon monoxide (CO) and carbon dioxide. In carbon monoxide, the ratio of the mass of carbon to the mass of oxygen is approximately 1:1, while in carbon dioxide, the ratio is approximately 1:2. These ratios are simple whole numbers, as predicted by the Law of Multiple Proportions.

Q.3 : Why is the Law of Multiple Proportions important in chemistry?

Ans.    The Law of Multiple Proportions is important for several reasons: It helps predict compound formation by understanding the simple whole-number ratios in which elements combine. It provides evidence for the atomic theory by demonstrating fixed ratios of elements in compounds. It is foundational in stoichiometry, aiding in determining reactant and product proportions in chemical reactions. Numerous experiments have confirmed its validity, establishing its significance in understanding chemical combinations.

Q.4 : How does the Law of Multiple Proportions support the atomic theory?

Ans.    The Law of Multiple Proportions supports the atomic theory by demonstrating that elements combine in fixed ratios, consistent with the idea of discrete atoms combining to form compounds. The observation of simple whole-number ratios in compound compositions aligns with the concept of atoms combining in specific proportions.

Q5 : Can you provide a simple explanation of the Law of Multiple Proportions?

Ans.    The Law of Multiple Proportions tells us that when elements combine to form different compounds, the ratio of their masses will be in simple whole numbers. For instance, if Element A combines with Element B to form two compounds, the masses of Element A that combine with a fixed mass of Element B will be in ratios like 1:1, 1:2, 2:3, and so on, where the numbers are simple whole numbers. This law helps us understand the consistent patterns in compound formations.
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