Chemistry Essay

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St Andrew’s Junior College Revision Questions – Redox 1. Balance the following equations: (a) V2+ + MnO4- → V3+ + Mn2+ (in acidic medium) (b) SO32- + I2 → SO42- + 2I - (in acidic medium) (c) C2O42- + Cr2O72- → CO2 + Cr3+ (in acidic medium) (d) HClO + Fe2+ → Cl2 + Fe3+ (in acidic medium) (e) CH3OH + MnO4- → CO2 + MnO2 (in alkaline medium) (f) Pb2+ + MnO4- → Pb4+ + MnO2 (in alkaline medium) 2. A solution of Y5+ can be oxidized to YO22+ by acidified Cr2O72-. (a) Write the equation for the reaction. (b) Calculate the volume of 0.2M UO3- needed to react with 20.00 cm3 of 0.1M Cr2O72-. 3. 24.40 g of hydrated iron(II) sulphate, FeSO4.xH2O was dissolved and made up to 1.0 dm3 of aqueous solution, acidified with sulphuric acid. 25.00 cm3 of the solution was titrated with 20.00 cm3 of 0.022M potassium manganate(VII) solution for complete oxidation. a) Write the equation for the reaction. b) Calculate the number of moles of Fe2+ present in 1.0 dm3 of the solution. c) Calculate the molar mass of hydrate iron(II) sulphate. Hence calculate the value of x. 4. Chlorine, Cl 2, is a strong oxidizing agent found in bleach. 10.0 cm3 of bleach solution was added to 25.0 cm3 of 0.4M Sn2+ solution acidified with sulphuric acid and made up to 100 cm3. 10.0 cm3 of the resulting solution containing the unreacted Sn2+ was titrated against 0.02M K2Cr2O7. Given that 11.40 cm3 of K2Cr2O7 was required for complete oxidation, a) Calculate the numbers of moles of Cr2O7- used. b) Calculate the number of moles of Sn2+ that react with Cl2. c) Calculate the concentration of Cl2 in bleach. 5. Pyrolusite is a manganese ore containing mainly manganese (IV) oxide, MnO2. MnO2 is reduced to Mn2+ when Fe2+ is oxidised Fe3+. 10.00 g of pyrolusite is dissolved in 200 cm3

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