RI 01. Redox Reactions Tutorial (Questions)

-1- Raffles Institution Year 5 H2 Chemistry 2025 Tutorial 1 – Redox Reactions Self-Check Questions 1 Determine the oxidation number of the underlined element in the following species: (a) BaSO4 (c) TiO2+ (e) H2O2 (g) BrF (b) Na3VO4 (d) C2O42− (f) N2O4 (h) IF7 2 Identify if the following equations represent a redox or non-redox reaction. Determine the change in oxidation number for the relevant element to support your answer. (a) NH3(aq) + HCl(aq) → NH4Cl(aq) (b) 3Mg(s) + 2NH3(g) → Mg3N2(s) + 3H2(g) 3 A Level N2010/III/4(f) Ozone is usually made by passing oxygen gas through a tube between two highly charged electrical plates. 3O2(g) → 2O3(g) The reaction does not go to completion, so a mixture of the two gases results. The concentration of O3 in the mixture can be determined by its reaction with aqueous KI. O3 + 2KI + H2O → I2 + O2 + 2KOH The iodine formed can be estimated by its reaction with sodium thiosulfate. 2Na2S2O3 + I2 → Na2S4O6 + 2NaI When 500 cm 3 of an oxygen/ozone gaseous mixture at s.t.p. was passed into an excess of aqueous KI, and iodine titrated, 15.0 cm3 of 0.100 mol dm–3 Na2S2O3 was required to discharge the iodine colour. (a) Calculate the amount in moles of iodine produced. (b) Hence calculate the percentage of O3 in the gaseous mixture. 4 A Level N2009/III/3(c) When sodium is burned in air, a mixture of sodium oxide, Na2O, and sodium peroxide, Na2O2, is formed. The mixture reacts with water according to the following equations. Na2O + H2O → 2NaOH Na2O2 + 2H2O → 2NaOH + H2O2 The following information will allow you to calculate the relative amounts of the two oxides produced when sodium is burned. • The mixture obtained by burning a sample of sodium was dissolved in distilled water and made up to 100 cm3 to give solution H. • A 25.0 cm3 portion of solution H was titrated with 0.100 mol dm–3 HCl. 22.50 cm3 of acid was required to reach the end-point.

-2- NaOH(aq) + HCl(aq) → NaCl(aq) + H2O(l) • The H 2O2 content of solution H was found by titration of another 25.0 cm 3 portion with 0.0200 mol dm–3 KMnO4 in acidic medium. 10.0 cm3 of KMnO4 solution was required to reach the end-point. 2MnO4−(aq) + 5H2O2(aq) + 6H+(aq) → 2Mn2+(aq) + 5O2(g) + 8H2O(l) (a) Using the results of the HC l titration, calculate the total amount of NaOH in 100 cm 3 of solution H. (b) Using the results of the KMnO 4 titration, calculate the amount of H 2O2 in 100 cm3 of solution H. (c) Hence, calculate the amount of Na2O and Na2O2 formed during the burning of the sodium sample. Suggested solutions to the self -check questions are appended behind the practice questions. Please use these solutions to check through your working and your final answers. Consult your tutor if you have any questions. Practice Questions 5 Identify if the following equations represent a redox or non-redox reaction. Dete