The Law of Constant Composition

This idea - that once a chemical formula for a compound is established, that compound always has the same formula - is expressed in the law of constant composition  

A compound always contains the same elements in the same proportions by mass, no matter how that compound is prepared. 

Constant mass proportions were originally determined by analysing the compound copper carbonate, CuCOa, in the 1790s. We now know that no matter how the copper carbonate is prepared it always contained atoms of copper, carbon, and oxygen in the proportions 1 1 3. 

Any scientific law summarizes the observations made in experiments by very many people. A law is only called a Law when, whenever it is tested by experiment, it is found to hold true. (It is always a big event in science when someone produces an experimental result, which can be repeated by many other scientists, which contradicts a Law The Law then has to be scrapped and replaced by something better.) 

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The law of constant composition This tells us that a compound always contains the same elements in the same proportions by mass. If the atom ratio of the elements in a compound is fixed (postulate 3), their proportions by mass must also be fixed. 

Two basic laws of chemistry are the law of conservation of mass and the law of constant composition. Which of these laws (if any) do the following statements illustrate ... 

Using the laws of constant composition and the conservation of mass, complete the molecular picture of hydrogen molecules (O—O) reacting with chlorine molecules ( — ) to give hydrogen chloride ( —O) molecules. 

Mercury(II) oxide, a red powder, can be decomposed by heating to produce liquid mercury and oxygen gas. When a sample of this compound is decomposed, 3.87 g of oxygen and 48.43 g of mercury are produced. In a second experiment, 15.68 g of mercury is allowed to react with an excess of oxygen and 16.93 g of red mercury(II) oxide is produced. Show that these results are consistent with the law of constant composition. 

Scientists are always on the lookout for patterns. When a pattern is observed in the data, it can be stated as a scientific law, a succinct summary of a wide range of observations. For example, water was found to have eight times the mass of oxygen as it has of hydrogen, regardless of the source of the water or the size of the sample. One of the earliest laws of chemistry summarized those types of observations as the law of constant composition, which states that a compound has the same composition regardless of the source of the sample. 

D the law of constant composition This question covers NSCS BS. This question tests the material that was covered in the textbook on pages 490-491. 

All three samples of magnesium oxide had the same O/Mg mass ratio. This is an example of the Law of Constant Composition. 

In the two decades between Lavoisier s Traite and Daltons New System of Chemical Philosophy, we find a conscious effort to accommodate chemical knowledge to a systematic compositional framework. This assimilation was organized through the new nomenclature and the operational concept of simple body. At the same time, there was a great increase in the gathering of quantitative data and attempts to find rational patterns to incorporate them. The results anticipated empirically the laws of constant composition and multiple proportion that reached full rationality in Dalton s atomic theory early in the next century. 

A compound is an electrically neutral substance that consists of two or more different elements with their atoms present in a definite ratio. Water, for instance, is a compound of hydrogen and oxygen, with two hydrogen atoms for each oxygen atom. Whatever the source of the water, it has exactly the same composition indeed, a substance with a different ratio of atoms would not be water Chemists took a big step forward when they first noticed this invariance of composition, for it suggested an underlying order in nature. They summarized the observation as the law of constant composition. The law was important historically, because it suggested to chemists that compounds consisted of specific combinations of atoms. 

The ratio of atoms within a chemical compound is usually constant. Compounds are made up of fixed proportions of elements they have a fixed composition. Chemists call this the Law of constant composition. 

The law of definite proportions, sometimes called the law of constant composition, was established in 1799 by Joseph Proust. He said a given compound always contained the same elements in the same proportion by mass. For example, water is always 88.9% oxygen by mass and 11.1% hydrogen by mass. 

In this experiment we will verify that the empirical formula of copper(II) chloride is CuCl2, and in so doing, demonstrate the Law of Constant Composition. We will do this by reducing a known weight of copper(II) chloride with aluminum to elemental copper. The reaction is shown by the following equation ... 

The formation of a compound from pure components is independent of the source of the material or of the method of preparation. If elements chemically react to form a compound, they always combine in definite proportions by weight. This concept is known as the Law of Constant Composition. 

The foundations of chemistry were now more or less completed. Phlogiston had been slain, and Lavoisier s theory of burning was safely established. De Morveau s new chemical nomenclature had been accepted, and Dalton had promulgated his atomic theory, which clearly explained two cornerstones of the structure of chemistry—the Laws of Constant Composition and Multiple Proportions. 

Law of Definite Proponion is also known as the Law of Definite Composition or the Law of Constant Composition . 

It is accordingly the definite struc ture of crystals and c)f nioteculcs that is responsible for the experimental observations that led to the formulation of the law of constant composition, or law of definite proportions. 

Chemical Laws - The Law of Constant Composition and the Law of Conservation of Mass... 

Percentage Composition, and using the Law of Constant Composition to find the Empirical and Chemical Formula of a Compound... 

Dalton, John. (1766-1844). The first theorist since the Greek philosopher Democritus to conceive of matter in terms of small particles. The founder of the atomic theory on which all succeeding chemical investigation has been based (1807). His essential concept of the indivisibility of the atom was not called into question until 1910 when radioactive decay was established by Rutherford. Dalton s theories relating to pressures of gases and atomic combinations led to the basic generalizations stated in the law of multiple proportions, the law of constant composition, and the law of conservation of matter. 

Furthermore, we may say that a compound is a pure substance consisting of two or more different elements in a fixed ratio. Water is 11.1% hydrogen and 88.9% oxygen by mass. Similarly, carbon dioxide is 27.3% carbon and 72.7% oxygen by mass, and calcium oxide (the white solid A in the previous discussion) is 71.5% calcium and 28.5% oxygen by mass. We could also combine the numbers in the previous paragraph to show that calcium carbonate is 40.1% calcium, 12.0% carbon, and 47.9% oxygen by mass. Observations such as these on innumerable pure compounds led to the statement of the Law of Definite Proportions (also known as the Law of Constant Composition) ... 

This law, also known as the Law of Constant Composition, can now be extended to include its interpretation in terms of atoms. It is so important for performing the calculation in this chapter that we restate it here ... 

More significant still, in 1799 Proust had put forward the Law of Fixed Proportions, according to which When combination between elements takes place, it is In definite proportions by weight, so that the composition of a pure cheonical compound is independent of the way in w hich it is prepared. This law, also known as the Law of Constant Composition, may be restated in the words The same compound always contains the same elements combined together in the same proportions by weight. 

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