Law of Constant or Definite Proportion
Law of Constant or Definite Proportion
Law of Constant Proportions or Law of Definite Proportions: French chemist, Joseph Proust analysed the chemical composition (types and percentage of elements present) of a large number of compounds and came to the conclusion that the proportion of each element in a compound is constant (or fixed), irrespective of where the compound came from or who prepared it. On this basis he proposed the law of constant proportions, according to which “In a chemical substance (or compound), the elements are always present in definite proportions (or ratios) by mass.”
Example: In a compound such as water, the ratio of the mass of hydrogen to the mass of oxygen is always 1: 8, whatever the source of water. Thus, if 9 g of water is decomposed, 1 g of hydrogen and 8 g of oxygen are always obtained. Similarly, carbon dioxide () always contains carbon and oxygen in the ratio of 3: 8. If a sample of
contains 36 g of carbon then it is compulsory that the sample has 96 g Oxygen.
Example: Copper oxide was prepared by two different methods. In one case, 1.75 g of the metal gave 2.19 g of oxide. In the second case, 1.14 g of the metal gave 1.43 g of the oxide. Show that the given data illustrate the law of constant proportions.
Case l : Mass of copper = 1.75 g And mass of copper oxide = 2.19 g.
So, mass of oxygen = Mass of copper oxide — Mass of copper = 2.19 — 1.75 = 0.44g
Now, in first sample of copper oxide compound. Mass of copper : Mass of oxygen = 1.75 : 0.44 = 3.98 : 1 = 4: 1
Case 2: Mass of copper = 1.14g And mass of copper oxide = 1.43 g.
So, mass of oxygen = Mass of copper oxide — Mass of copper = 1.43 — 1.14 = 0.29g
Now, in second sample of copper oxide compound. Mass of copper : Mass of oxygen
=1.14:0.29 = 3.93:1 =4 : 1
From the above calculations we can see that the ratio (or proportion) of copper and oxygen elements in the two samples of copper oxide compound is the same, i.e. 4: 1. So, the given data verify the law of constant proportions.
| ELEMENT | SYMBOL | ATOMIC NUMBER | ATOMIC MASS |
| HYDROGEN | H | 1 | 1 |
| HELIUM | He | 2 | 4 |
| CARBON | C | 6 | 12 |
| NITROGEN | N | 7 | 14 |
| OXYGEN | O | 8 | 16 |
| FLUORINE | F | 9 | 19 |
| SODIUM | Na | 11 | 23 |
| MAGNESIUM | Mg | 12 | 24 |
| SULPHUR | S | 16 | 32 |
| CHLORINE | Cl | 17 | 35 |
In a compound such as water, the ratio of the mass of hydrogen to the mass of oxygen is always 1: 8, whatever the source of water. If 18 g of water is decomposed, then how much grams of hydrogen we get ? | |||
| Right Option : B | |||
| View Explanation | |||
(1) burning sulphur in oxygen, (2) reaching sodium sulphite with dilute (3) heating copper with conc. And it was found that in each case sulphur and oxygen combined in the ratio of 1:1. The data illustrates the law of: | |||
| Right Option : C | |||
| View Explanation | |||
The percentage by weight of | |||
| Right Option : C | |||
| View Explanation | |||
Students / Parents Reviews [10]
I have spent a wonderful time in Abhyas academy. It has made my reasoning more apt, English more stronger and Maths an interesting subject for me. It has given me a habbit of self studying
Yatharthi Sharma
10thOne of the best institutes to develope a child interest in studies.Provides SST and English knowledge also unlike other institutes. Teachers are co operative and friendly online tests andPPT develope practical knowledge also.
Aman Kumar Shrivastava
10thAbhyas Methodology is very good. It is based on according to student and each child manages accordingly to its properly. Methodology has improved the abilities of students to shine them in future.
Manish Kumar
10thBeing a parent, I saw my daughter improvement in her studies by seeing a good result in all day to day compititive exam TMO, NSO, IEO etc and as well as studies. I have got a fruitful result from my daughter.
Prisha Gupta
8thA marvelous experience with Abhyas. I am glad to share that my ward has achieved more than enough at the Ambala ABHYAS centre. Years have passed on and more and more he has gained. May the centre flourish and develop day by day by the grace of God.
Archit Segal
7thMy experience with Abhyas is very good. I have learnt many things here like vedic maths and reasoning also. Teachers here first take our doubts and then there are assignments to verify our weak points.
Shivam Rana
7thIt has a great methodology. Students here can get analysis to their test quickly.We can learn easily through PPTs and the testing methods are good. We know that where we have to practice
Barkha Arora
10thIt was a good experience with Abhyas Academy. I even faced problems in starting but slowly and steadily overcomed. Especially reasoning classes helped me a lot.
Cheshta
10thMy experience was very good with Abhyas academy. I am studying here from 6th class and I am satisfied by its results in my life. I improved a lot here ahead of school syllabus.
Ayan Ghosh
8thIt was good as the experience because as we had come here we had been improved in a such envirnment created here.Extra is taught which is beneficial for future.
