Chapter 4 Chemical Reactions (Lecture 7-8)done

Chapter 4 Chemical Reactions (Lecture 7-8)done - Chapter 4...

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Chapter 4 Chemical Reactions 4.1 Ionic Theory of Solutions and Solubility Rules 4.2 Molecular and Ionic Equations 4.3 Precipitation Reactions 4.4 Acid-Base Reactions (need not to be covered, either not in syllabus or will be covered in detail in later chapters)
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Chapter 4 Chemical Reactions Oxidation-reduction reactions Oxidation number and rules to assign Half-reactions : oxidation and reduction Oxidized and reduced species Oxidizing agent and reducing agent 4 types of redox reactions
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4.5 Oxidation Number Oxidation number signifies the number of charges the atom would have in a molecule (or an ionic compound) if electrons were transferred completely. Fe 2+ :Oxidation number : +2 Oxidation state : (II) Used to keep track of e- in a reaction To determine if e- have been transferred from one atom to another
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Rules: 1. In free elements (that is, an element not combined chemically with a different element), each atom has an oxidation number of zero. Thus each atom in H 2 , Br 2 , Na, Be, P 4 and O 2 has the same oxidation number: zero. 1. For ions composed of only one atom (that is, monatomic ions) the oxidation number is equal to the charge on the ion. 1. The oxidation number of oxygen in most compounds (for example: MgO and H 2 O) is –2, but in hydrogen peroxide (H 2 O 2 ) and peroxide ion (O 2 2- ), it is –1. 4. The oxidation number of hydrogen is +1, except when it is bonded to metals in binary compound. In these cases (for example: LiH, NaH, CaH 2 ), its oxidation number is –1.
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1. Fluorine has an oxidation number of –1 in all its compounds. Other halogens (Cl, Br, and I) have negative oxidation numbers when they occur as halide ions in their compounds. When combined with oxygen – for example in oxoacids and oxoanions – they have positive oxidation numbers. 2. In a neutral molecule, the sum of the oxidation numbers of all the atoms must be zero: CO 2 , FeSO 4 , NaCl . 3. In a polyatomic ion, the sum of oxidation numbers of all the elements in the ion must be equal to the net charge of the ion: Cr 2 O 7 2 - , NO 3 - . Example: What are the oxidation number of a) Fe atom in FeCl 3 b) Cr atoms in Cr 2 O 7 2- c) Cl atoms in Cl 2 O 7 d) S atoms in Na 2 S 4 O 6 e) N atom in NH 4 +
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1) Oxidation – is an increase in oxidation number (the loss of electrons) 2) Reduction – is a decrease in oxidation number (the gain of electrons) A reaction in which atoms change oxidation numbers (implying) electrons are transferred between species Oxidation not necessarily involve oxygen e.g. Ca(s) + Cl 2 (g) → CaCl 2 (s) A substance is oxidized when it shows an increase in its oxidation number. This substance reacts as a reducing agent (reductant) in a chemical reaction. A substance is reduced when it shows a decrease in its oxidation
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This note was uploaded on 06/21/2009 for the course CHEM 130 taught by Professor Kia during the Spring '09 term at Abraham Baldwin Agricultural College.

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Chapter 4 Chemical Reactions (Lecture 7-8)done - Chapter 4...

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