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Miracle Learning Centre Chemistry Tuition Question on Redox Reactions. (O Level / IP Chemistry)

1 (a) A sample of manganese oxide was analysed and it was found that 11.0 g of manganese had combined with 4.8 g of oxygen. Find the empirical formula of the oxide.

(b) The reaction between manganese (IV) oxide and concentrated hydrochloric acid produces chlorine gas. MnO2 + 4 HCl MnCl2 + Cl2 + 2 H2O

(i) In terms of changes in oxidation states, state and explain which substance is behaving as an oxidising agent in this reaction. ……………………………………………………………………………..………... ……………………………………………………………………………………..
(ii) Explain how aqueous potassium iodide can be used to confirm that manganese (IV) oxide is an oxidising agent. ……………………………………………………………………………..………... ……………………………………………………………………………………..
(iii) 50 cm3 of chlorine gas was produced in the reaction at room temperature and pressure. What was the mass of MnO2 used?

(iv) The chlorine gas produced is bubbled into a solution of sodium bromide. Write an ionic equation for the reaction and describe the observations that will be made. ……………………………………………………………………………..………... ……………………………………………………………………………..………... ……………………………………………………………………………………..
Miracle Learning Centre Answer to Chemistry Tuition Question on Redox Reactions. (O Level / IP Chemistry) 1 (a) Mass (g) No. of moles Simplest ratio Mn 11.0 0.2 1 O 4.8 0.3 1.5 Empirical formula: Mn2O3

(b) (i) MnO2. The oxidation state of Mn decreases from +4 in MnO2 to +2 in MnCl2. Oxidising agents are reduced during reaction.
 (ii) KI is a reducing agent. The presence of an oxidizing agent like MnO2 will oxidize KI, causing it to turn from colourless to brown.
 (iii) No. of moles of Cl2 = (50/1000)/24 = 2.0833 x 10-3 No. of moles of MnO2 = 2.0833 x 10-3 Mass of MnO2= 2.0833 x 10-3 X (55 + 2 x 16) = 0.181g (to 3 s.f.)
 (iv) Cl2 + 2Br -  Br2 + 2Cl- The colourless solution will turn reddish-brown. Learn from our Chemistry Tuition Questions and Answers. Miracle Learning Centre Call 6463 8756 or sms 8128 8342/9839 9908. (Specialist in Science and Maths) for Primary, Secondary and JC levels. Miracle Learning Centre specialises in Chemistry tuition, Physics tuition, Maths tuition and Science tuition Classes.