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Law of Reciprocal Proportion

Introduction to Law of Reciprocal Proportion

Last updated date: 28th Mar 2023
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German chemist Jeremias Richter devised a simple method for comparing compounds and determining how two elements will combine to make another chemical in the late 18th century.

Law of <a href=''>Reciprocal</a> Proportion

Law of Reciprocal Proportion

Jeremias Ritcher put forward the law of reciprocal proportions in 1792. According to the law of reciprocal proportions, we may calculate the proportion of elements in compound AC if we know the proportion of elements in compounds AB and BC. This law aided in our understanding of stoichiometry, which is the process of calculating the amounts of reactants and products in relation to reactions.

History of The Scientist

Jeremias Benjamin Richter (1762 - 1807),

Jeremias Benjamin Richter (1762 - 1807)

Name: Jeremias Benjamin Richter

Born: 10 March 1762

Died: 4 May 1807

Field: Chemist

Nationality: German

What is the Law of Reciprocal Proportion?

The rule of reciprocal proportions is another name for the law of reciprocal proportions, which is also referred to as the law of equivalent proportions or permanent ratios.

According to Ritcher, "When two elements combine independently with a fixed mass of the third element, the ratio of their masses at that time is either the same or some whole number multiple of the ratio they mix."

Law of Reciprocal Proportion Examples

S. No


Combining Elements

Combining Weights



12 4


C 0

12 32

  • Let's take methane and calculate the ratio of the components. Hydrogen has a molecular weight of 1 g/mol, and carbon has a molecular weight of 12 g/mol. Since there are 4 hydrogen atoms for every carbon atom, the ratio is 12:4, which can be expressed as 3:1.

  • Therefore, both hydrogen and another element can be found in methane and water. This law states that the ratio of carbon to oxygen, which makes up the other element in both molecules, should be 3:8, or a straightforward multiple of that ratio.

  • We obtain 3:8 because water has an oxygen to carbon ratio of 8, and methane has an oxygen to carbon ratio of 3. Let's check to see whether this is accurate: the ratio of carbon to oxygen in carbon dioxide is 12:32.

  • Let's look at another illustration, beginning with sodium chloride. The molecular weights of sodium and chloride are 23 and 35 g/mol, respectively. This makes the ratio 23:35.

  • Let's now examine hydrochloric acid with a 35:1 ratio. The ratio we would anticipate to observe if we combined salt and hydrogen is 23:1. Yes, these come together to produce sodium.

Limitations of Law of Reciprocal Proportion

  • Differences similar to those seen in the law of constant proportions are produced by the element's isotopes. The synthesis of a number of chemicals should thus use the same isotope or a combination of isotopes.

  • The law only applies to a tiny subset of products that exhibit the disputed property since there are only a finite number of elements that will combine with the third element and also with one another.

Applications of Law of Reciprocal Proportion

We can now understand stoichiometry thanks to this law. This is how the quantities of the reactants and products in relation to the reaction are calculated. The law that exists now makes sense because every element has a specific molecular weight. To create an elemental compound, each element is added in a ratio of whole numbers.

Solved Examples

1. What made the law of reciprocal proportions significant?

  1. It aided in the discovery of novel chemicals

  2. It contributed to our current understanding of stoichiometry.

  3. It assisted scientists in determining complex sizes.

  4. The periodic table was made possible by it.

Ans: The correct answer is option B. As the law of reciprocal proportions plays an important role in studying and understanding the basic rules of stoichiometry.

2. Carbon is found in three different compounds: carbon dioxide (27.27%), carbon disulfide (15.79%), and sulphur dioxide (50%) Clearly demonstrate how the data exemplifies the law of reciprocal proportions.


Carbon Compound

Carbon Compound

Let us take Carbon dioxide.

The percentage of carbon is 27.27

Percentage of oxygen (100 – 27.27) is 72.73

27.27 g of carbon reacts with 72.73 g of oxygen.

1 g of carbon joins with 72.73 / 27.27 => 2.67 g of oxygen.

Let us take Carbon disulfide.

Percentage of carbon = 15.79

Percentage of sulphur (100 – 15.79) is 84.21

15.79 g of carbon reacts with 84.21 g of sulphur.

Hence, 1 g of carbon reacts with \[\frac{84.21}{15.79}\] = 5.33 g of sulphur.

The ratio of different masses of sulphur and oxygen joining with a fixed mass of carbon is 5.33: 2.67.

That is, 2: 1. —> [1]

Let us take Sulphur Dioxide,

Percentage of sulphur = 50

Percentage of oxygen = 100 – 50 = 50

50 g of sulphur reacts with 50 g of oxygen.

The ratio of the mass of sulphur to oxygen is 50: 50,

That is, 1:1 —> [2]

A straightforward whole-number multiple of the first ratio is the second ratio. The information serves as an example of the law of reciprocal proportions.

3. Different oxygen content ratios in the various nitrogen oxides demonstrate the following law:

  1. The Law of reciprocal proportions

  2. The Law of multiple proportions

  3. The Law of constant proportions

  4. The Law of conservation of mass

Ans: Option A offers the right response. The law of multiple proportions, which states that when two elements combine in more than one proportion to form one or more compounds, the weight of one element that combines with the given weight of other elements is in the ratio of the small whole number, is demonstrated by the different proportions of oxygen in the various oxides of nitrogen.

Important Points to Remember

  • The rule of reciprocal proportions is another name for the law of reciprocal proportions, which is also referred to as the law of equivalent proportions or permanent ratios.

  • One of the fundamental laws of stoichiometry, along with definite and various proportions laws, is this one.

  • German physicist Jeremias Richter proposed the statute in 1791.


With the law's consent, tables of equivalent element weights might be made. These equivalent weights were frequently used by chemists in the nineteenth century. Two further stoichiometric laws are the law of definite proportions and the law of many proportions. The law of definite proportions is the formula for any compound formed between components A and B.

Competitive Exams after 12th Science

FAQs on Law of Reciprocal Proportion

1. What is the historical background behind the law of reciprocal proportions?

Richter developed the reciprocal proportions law while researching the rates at which metals are neutralised in the presence of acid. When two separate chemicals A and B, have affinities for two additional substances, C and D, the proportion of C and D that can saturate the same quantity of A is the same as that of C and D that can saturate the same amount of B. This was researched by Berzelius in the early 19th century. Later, Jean Stas demonstrated that these stoichiometric laws were accurate within the bounds of experimental error.

2. Is the law of reciprocal proportions a rule for combining chemicals?

Jeremias Richter created the Law of Reciprocal Proportions in 1792. It claims that if two different elements combine to form a third element with the same weight, their mass ratios will either be multiples of or equal to the mass ratio at which the combination took place. According to Dalton's theory of atomicity, each element's atoms are identical, and compounds are created by joining atoms from distinct elements in a ratio of whole numbers. Therefore, the weights of the components that combine with the weights of a fixed element should be in a straightforward ratio to the weights of the elements when they mix.

3. What is the atomic hypothesis of Dalton?

John Dalton, an English physicist and chemist, proposed the atomic hypothesis in 1808 as a scientific theory about the composition of matter. It claimed that tiny, indivisible particles called "atoms" make up all substances. According to Dalton, the idea of atoms can be used to explain the laws of specific ratios and the law of conservation of mass. Dalton proposed that everything is made of minuscule atoms and indivisible particles. They were "solid, massy, hard, impenetrable, moving particle(s)," according to his description.