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# Concentration of hpo 4 2 is 0100 m so we can

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concentration of HPO 4 -2 is 0.100 M, so we can substitute that into the expression we calculated in part (a): HPO 4 2- [ ] PO 4 3- [ ] = 4.8 0.100 PO 4 3- [ ] = 4.8 PO 4 3- [ ] = 2.09 x 10 -2 M Molar mass of K 3 PO 4 = 3 39.098 ( ) + 30.974 + 4 15.999 ( ) [ ] g mol -1 = 212.264 g mol -1 Mass of K 3 PO 4 = 2.09 x 10 -2 mol L 212.264 g mol -1 ( ) 1 L ( ) = 4.4363 g = 4 g We need to add 4 g of K 3 PO 4 to 1.0 L . (don’t take off points for significant figures) Oxidation-reduction problems D. Hydrogen peroxide (H 2 O 2 ) is a harmful and reactive byproduct of metabolism. To prevent H 2 O 2 from causing extensive oxidative damage to cells, the enzyme catalase catalyzes the conversion of H 2 O 2 to much less reactive molecules, oxygen and water. 2H 2 O 2 2H 2 O + O 2 Use oxidation numbers to identify which molecules are reduced and/or oxidized in this reaction. H 2 O 2 is both reduced to H 2 O (oxidation number of oxygen changes from -1 to -2) and oxidized to O 2 (oxidation number changes from -1 to 0). 3

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