Ch_04b_1009

Ch_04b_1009 - Applications of Precipitation Reactions 30...

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30 Applications of Precipitation Reactions 31 Example: What is the molarity of a Na 3 PO 4 solution if addition of AgNO 3 (aq) to 75.0 mL of this solution produces 0.205 g Ag 3 PO 4 (s)? First, write the balanced chemical equation: Na 3 PO 4 (aq) + AgNO 3 (aq) Ag 3 PO 4 (s) + NaNO 3 (aq) 3 3 Then, determine the amount of Na 3 PO 4 in moles. Ag 3 PO 4 : 3×107.87 + 30.97 + 4×16.00 = 418.58 g/mol 0.205 g Ag 3 PO 4 × 418.58 g Ag 3 PO 4 1 mol Ag 3 PO 4 1 mol Ag 3 PO 4 × 1 mol Na 3 PO 4 = 0.000490 mol Na 3 PO 4 Finally, calculate the concentration: 0.000490 mol Na 3 PO 4 V = 75.0 mL × 1000 mL 1 L = 0.0750 L solution 0.0750 L solution = 0.00653 M Na 3 PO 4
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32 4.3 Reactions Involving Oxidation and Reduction The largest category of reactions. often called redox reactions. 33 Oxidation and Reduction Chemical reactions often involve changes in oxidation states of atoms Oxidation states are represented by oxidation numbers Historically: Oxidation was used to mean “combining with oxygen”; Reduction was used to describe “removal of oxygen”.
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34 •An oxidation number is the charge on a monatomic ion, or a hypothetical charge assigned to an atom in a molecule or polyatomic ion by some rules. • Examples: in NaCl, the oxidation number of Na is +1, that of Cl is –1 (the actual charge). •In CO 2 (a molecular compound, no ions) the oxidation number of oxygen is –2, because oxygen as an ion would be expected to have a 2– charge. • The carbon in CO 2 has an oxidation number of +4. Oxidation Number 35 In binary compounds, group 7A elements have ON = – 1; 6A elements have ON = – 2; and group 5A elements have ON = – 3.
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This note was uploaded on 05/06/2008 for the course CHEM 103 taught by Professor Forgot during the Spring '07 term at CUNY City.

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Ch_04b_1009 - Applications of Precipitation Reactions 30...

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