ChE102 - Tutorial 8 Solutions - ChE102 Chemistry for...

This preview shows page 1 - 3 out of 5 pages.

ChE102 Chemistry for Engineers - Tutorial 8 Solutions Solve the following problems either individually or in small groups (3 students maximum). Submit one copy of the solutions per group. Ask the TA for help if you need assistance solving the problems. Problem 1 Identify whether the following reactions are redox reactions and balance the reactions appropriately. a) SiCl 4 (aq) → SiO 2 (s) + Cl - (aq) (basic media) b) As 2 O 3 (s) + NO 3 - (aq) → H 3 AsO 4 (aq) + NO(g) (acidic media) a) SiCl 4 (aq) → SiO 2 (s) + Cl - (aq) (basic media) This is not a redox reaction, the oxidation state of silicon (Si) and chlorine (Cl) do not change. To balance the reaction, first balance Si and Cl: SiCl 4 (aq) → SiO 2 (s) + 4 Cl - (aq) Next add OH - to balance the charge: SiCl 4 (aq) + 4OH - (aq) → SiO 2 (s) + 4Cl - (aq) Finally, add H 2 O to balance the oxygen and hydrogen. SiCl 4 (aq) +4OH - (aq) → SiO 2 (s) + 4Cl - (aq) + 2H 2 O b) As 2 O 3 (s) + NO 3 - (aq) → H 3 AsO 4 (aq) + NO(g) (acidic media) This is a redox reaction, the oxidation state of nitrogen decreases from +5 to +2 while the oxidation state of arsenic (As) increases from +3 to +5. Step 1: write the two half-reactions Oxidation: As 2 O 3 (s) H 3 AsO 4 (aq) Reduction: NO 3 - (aq) → NO(g) Step 2: balance everything other than hydrogen and oxygen As 2 O 3 (s) 2 H 3 AsO 4 (aq) NO 3 - (aq) → NO(g) Step 3: add H 2 O to balance oxygen As 2 O 3 (s) + 5H 2 O(l) 2H 3 AsO 4 (aq) NO 3 - (aq) → NO(g) + 2H 2 O(l) Step 4: add H + to balance hydrogen As 2 O 3 (s) + 5H 2 O(l) → 2H 3 AsO 4 (aq) + 4H + (aq) NO 3 - (aq) + 4H + (aq) → NO(g) + 2H 2 O(l) Step 5: balance charge by adding e -
As 2 O 3 (s) + 5H 2 O(l) → 2H 3 AsO 4 (aq) + 4H + (aq) + 4 e - NO 3 - (aq) + 4H + (aq) + 3 e - → NO(g) + 2H 2 O(l) Step 6: balance number of e - for each half-reaction add the two half-reactions 3 x (As 2 O 3 (s) + 5H 2 O(l) → 2H 3 AsO 4 (aq) + 4H + (aq) + 4 e - ) 4 x (NO 3 - (aq) + 4H + (aq) + 3 e - → NO(g) + 2H 2 O(l)) Overall: 3As 2 O 3 (s) + 4NO 3 - (aq) + 16H + (aq) + 15H 2 O(l) → 6H 3 AsO 4 (aq) + 4NO(g) + 8H 2 O(l) + 12H + (aq) Simplify the reaction: 3As 2 O

  • Left Quote Icon

    Student Picture

  • Left Quote Icon

    Student Picture

  • Left Quote Icon

    Student Picture