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Oxidaton-Reduction
Chemistry Regents June 2010 - Question 45 PDF Print E-mail
Written by The Chemistry Wizard   

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Answer: (1)

Why? Reduction, as it applies to reduction/oxidation (redox) reactions, is a loss of electrons. This means oxidation is the gaining of electrons. Reduction and oxidation can also be defined by the oxidation state of the atom. An increase in oxidation state is called oxidation, while a decrease in oxidation state is termed reduction. The oxidation state is loosely equated to the charge present on the atom.

Answering the Question:

The question refers to the reduction of iron(II) ions. Analyzing the half reactions of the answers, only answers (1) and (4) are equations showing the loss of an electron. However, only answer (1) is showing that loss of electron from an iron(II) ion. A half reaction equation is a convenient way to express the movement of electrons going from reactants to products. Iron is a transition metal and can exist in a number of transition states or oxidation states, mainly as iron(II) written Fe2+ and iron(III) Fe3+. Therefore, answer (1) is the correct answer.
 
Chemistry Regents June 2010 - Question 80 PDF Print E-mail
Written by The Chemistry Wizard   

image080

Answer: Cu2O

Answering the Question: Copper (I) oxide is a very common oxide of copper. The (I) denotes that copper has an oxidation state of one, and can be written Cu+. Since oxygen will accept two electrons to form a stable configuration, it will require two Cu+, since each copper will donate only one electron towards the bond. The resulting chemical formula of cuprite would be Cu2O
 
Chemistry Regents June 2010 - Question 81 PDF Print E-mail
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Written by The Chemistry Wizard   

image081

Answer: The oxidation number is (II)

Answering the Question:

The oxidation number of a chemical species is normally the charge associated with the species when the binding ligand is removed along with the shared central atom. For the molecule Cu2CO3(OH)2 the charge of each species that is a part of the molecule, needs to be determined.

Therefore:

OH would have a char of -1 and would be written OH-. Since two of them are present the charge contributing to the overall molecule is 2 electrons.

CO3 would have a net charge of 2-; this is necessary as the copper present in the molecule is copper (II). The oxidation number of copper was determined from the determination of charge of OH-. Since two OH- are present in the chemical formula and there is no net charge on the molecule, it means that the oxidation number of Cu would have to be 2+ to accommodate them all. The CO3 molecule usually has a charge of 2-. Carbon is able to four electrons, while typically oxygen will only accept 2. This means that at any point in time carbon will be double bonded to an oxygen atom and single bonded to two others. However, the molecule has symmetry, which would indicate a sharing of the electrons to form the diagram below.

image081-diagram1

Which can be summarized in the diagram below.

image081-diagram2

 

 

 


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