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Chapter 4 Answers

Chapter 4 Answers - Chemistry 141 Lecture Dr Ben Tovrog...

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Chemistry 141 Lecture Dr. Ben Tovrog Chapter 4 Supplemental Problems - Answers 1. Assign the oxidation number to each atom in the following elements, molecules and ionic substances: a) CCl 4 b) CH 4 c) HNO 3 d) Ca(NO 3 ) 2 e) K 2 Cr 2 O 7 f) Ag C = +4 C = -4 H = +1 Ca = +2 K = +1 Ag = 0 Cl = -1 H = +1 O = -2 O = -2 O = -2 N = +5 N = +5 Cr = +6 g) I 2 h) Fe 2 O 3 i) CO 2 j) SF 6 k) NH 4 Cl l) O 2 I = 0 O = -2 O = -2 F = -1 Cl = -1 O = 0 Fe = +3 C +4 S = +6 H = +1 N = -3 2. Assign the oxidation number to each atom in the following ions: a) Ni 2+ b) CO 3 2- c) MnO 4 - . d) SO 4 2- e) PO 4 3- f) NO 3 - Ni = +2 O = -2 O = -2 O = -2 O = -2 O = -2 C = +4 Mn = +7 S = +6 P = +5 N = +5 3. For the following reactions identify if it is or isn’t an oxidation reduction reactions. If it is a redox reaction, identify the oxidizing agent, the reducing agent, the substance being oxidized and the substance being reduced. Identify the oxidation number changes which support those identifications. A) Zn (s) + 2 HCl (aq) ZnCl 2 (aq) + H 2 (g) Redox rxn. Zn oxidized (and is reducing agent) Zn ox # 0 -> +2 HCl reduced (and is oxidizing agent) H ox # +1 -> 0. B) Cr 2 O 7 2- (aq) + 2 OH - 2 CrO 4 2- (aq) + H 2 O (l) Not a redox rxn. Cr ox # is +6 in both reactant and product. C) 3 H 2 (g) + N 2 (g) 2 NH 3 (g) Redox rxn. H 2 oxidized (and is reducing agent). H ox # 0 -> +1. N 2 reduced (and is oxidizing agent) N ox # 0 -> -3 D) Ag + (aq) + Cl - (aq) AgCl (s) Not a redox reaction. No change in ox #. E) 3 Cu (s) + 8 H + (aq) + 2 NO 3 - (aq) 3 Cu 2+ (aq) + 2 NO (g) + 4 H 2 O
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Redox rxn. Cu oxidized (and is reducing agent) Cu ox # 0 -> +2 NO 3 - reduced (and is oxidizing agent) N ox # +5 -> +2. 4. For the following identify the type of reaction, the substance oxidized and the substance reduced. If the reaction is not a redox reaction, indicate as such. A) (NH 4 ) 2 CO 3 (s) 2 NH 3 (g) + H 2 O (l) + CO 2 (g) Decomposition reaction. Not a redox reaction. B) HClO 4(aq) + NaOH (aq) H 2 O (l) + NaClO 4 (aq) Acid – base reaction. Not a redox reaction. C) 2 Cu (s) + O 2 (g) 2 CuO (s) Combination reaction. Is a redox rxn: Cu oxidized (Cu ox # 0 -> +2) O 2 reduced (O 2 ox # 0 -> -2). 5. Barium sulfate is a strong electrolyte. If you dissolve 100 g. of barium sulfate in 400 ml of water, what are the concentrations of the ions present in solution? BaSO 4 (s) Ba 2+ (aq) + SO 4 2- (aq) 100 g / 233.37 g/mol = 0.429 mol. M (Ba 2+ ) = M (SO 4 2- ) = 0.429 mol / 0.400 L = 1.073 M. 6. Potassium dichromate forms a brilliant yellow solution when it is dissolved in water. If you dissolve 220 g of potassium dichromate in 750 ml of water, what ions are in solution? What are their concentrations (molarity)?
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