Expt 3 - The Empirical Formula of Selected Hydrates - FA 2009

Expt 3 - The Empirical Formula of Selected Hydrates - FA 2009

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1 THE EMPIRICAL FORMULA OF SELECTED HYDRATES ADDITIONAL READING The concepts in this experiment are also discussed in Sections 1.7, 1.8, 2.8, 3.9, and on page 86 of Principles of Chemistry – A Molecular Approach , by Tro. ABSTRACT Each student is expected to perform the experiment individually. You will carry out a decomposition reaction of two hydrate salts; heat will be used to drive off the water (dehydration). Ultimately you will determine the mass percent of water present in these compounds and their empirical formulas. You will also determine the empirical formula using the molar ratio of water-to-salt. BACKGROUND CHEMICAL COMPOUNDS All matter is made up of tiny indestructible particles called atoms. As you will learn in this course, these atoms can be manipulated and combined to make more complex structures called chemical compounds or molecules. Since atoms are indestructible, it makes sense that a molecule must be made up of a whole number of atoms , meaning you can not have a fraction of an atom. For example, water is made up of two hydrogen atoms (represented by the symbol H) and one oxygen atom (represented by the symbol O); the chemical formula of water is H 2 O. The chemical formula H 2 O is the chemist’s short hand notation for water. In this course, you will be bombarded with many chemical formulas. It is important that you become familiar with them. In addition to a whole number of atoms, there is also the requirement that the law of definite proportions be obeyed, which states that all samples of a given compound, regardless of their source or how they were prepared, have the same proportions of their constituent elements . For example, all water molecules are H 2 O. It is not possible to have water that has a chemical formula of H 3 O 2 . Similarly carbon dioxide (which you exhale with every breath), has two oxygen atoms and one carbon atom in each CO 2 molecule. This does not mean that H and O, and C and O can not combine in different ways. For example H 2 O 2 and CO are the chemical formulas for hydrogen peroxide and carbon monoxide, respectively. They are not the formulas for water and carbon dioxide; these chemical compounds have very different formulas and very different properties. Hydrogen peroxide is a very reactive liquid that is used as rocket fuel; carbon monoxide is a poisonous gas produced as a byproduct when gas or oil is burned. You may even have a carbon monoxide detector in your home to warn you if your furnace is producing too much carbon monoxide. Although these chemical compounds are made up of the same kinds of elements, H and O for water (H 2 O) and hydrogen peroxide (H 2 O 2 ) and C and O for carbon monoxide (CO) and carbon dioxide (CO 2 ), they are in different proportion. The ability to make multiple compounds from the same types of atoms is called the law of multiple proportions . EMPIRICAL FORMULA
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This note was uploaded on 04/19/2011 for the course CHEM 1033 taught by Professor Price during the Fall '10 term at Temple.

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Expt 3 - The Empirical Formula of Selected Hydrates - FA 2009

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