Redox: Analysis Of The Oxidizing Capacity Of Bleach

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Experiment 8: Redox: Analysis of the Oxidizing Capacity of Bleach
PURPOSE
In this experiment, you will show how redox reactions can be used to quantitatively determine the amount of oxidizing agent in liquid hypochlorite household bleach.
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Therefore, from the volume of thiosulfate that is required to react with the liberated iodine and the weight of the bleach sample, the percentage by mass of oxidizing agent can be calculated.
Example: An excess of KI was added to a 0.501g sample of bleach. The liberated iodine required 10.21 mL of 0.06292M Na2S2O3 solution for the titration to reach the end point. What is the oxidizing capacity of the NaOCl in the bleach?
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CH204 Experiment 8: The Analysis of Household Bleach spring 2015
Two moles of Na2S2O3 are required for every mole of hypochlorite in the reaction.
 0.0692mol Na2S2O3  1mol NaClO  −4 (0.01021L Na2S2O3 ) L Na S O  2mol Na S O  =3.53×10
 223  223 Convert the moles of NaClO to grams of NaClO:
0.501 g
Oxidation-Reduction Reactions:
Reactions that involve the transfer of electrons from one reactant to another reactant, regardless of the substances involve, are collectively called oxidation-reduction reactions (redox). The reactants in these reactions will lose or gain electrons and change their charge (oxidation number) as they form the products.
• Oxidation is the process in which a substance in a chemical reaction loses
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All naturally occurring diatomic molecules have zero oxidation states.
0000000 Br2 I2 N2 Cl2 H2 O2 F2
c. For simple Group A binary ionic compounds (salts), the oxidation state is the charge of the element:
i. Metals (Group I A, IIA, and IIIA) are assigned a positive oxidation state – determined by the number of electrons the element has lost.
• Group IA metals+1 (Li+, Na+, K+, Rb+, Cs+)
• Group IIA metals+2 (Mg2+, Ca2+, Sr2+, Ba2+)
• Group IIIA metals+3 (Al3+, Ga3+, In3+) ii. Nonmetals (Group VA, VIA, VIIA) are assigned a negative oxidation state determined by the number of electrons the element has gained.
d. Hydrogen, H, has an oxidation number of +1 unless it is combined with metals, where it has the oxidation number -1. ExamplesLiH, BaH2
e. Oxygen usually has the oxidation number –2.
Exceptions:
• In peroxides O has oxidation number of –1. Examples: H2O2, CaO2, Na2O2
• In OF2, O has oxidation number of +2. (Fluorine is the most electronegative element and has the greater share of electrons.)
f. ATOMS IN SUBSTANCES CAN HAVE FRACTIONS AS OXIDATION NUMBERS. 2.5 -2
• Example: S4O62−, the oxidation state of the sulfur in the tetrathionate ion has an oxidation number of

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