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Unit 3 Redox

Unit 3 Redox

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Unit 3 Redox

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  1. Unit 3 Redox

  2. Go to question 1 2 3 4 5 6 7 8

  3. 1 Cr2O72- (aq) + 14H+ + 6e 2Cr 3+ (aq) + 7H2O (l) I2 (aq) + 2e- 2I -(aq) How many moles of I2 are reduced by 1 mole of Cr2O72-ions? a. 4 b. 3 c. 2 d. 1

  4. a hint!!!! 1st hint The number of electrons on both sides of the redox equation must balance. 2nd hint How many more moles of Iodine are now needed?

  5. Cr2O72- (aq) + 14H+ + 6e 2Cr 3+ (aq) + 7H2O (l) I2 (aq) + 2e- 2I-(aq) How many moles of I2 are reduced by 1 mole of Cr2O72- ions? Correct because….. The number of electrons lost and gained must be equal. X 3 Cr2O72-(aq) + 14H+(aq) + 3I2 (aq) 2Cr 3+ (aq) + 7H2O (l) +6I-(aq) Ans: b. 3

  6. Which of the following is not a redox reaction. 2 a. Mg (s) + 2HCl (aq) MgCl2 (aq) + H2 (g) b. CuCO3 (s) + H2SO4 (aq) CuSO4(aq) + CO2 (g) +H2O (l) c. Zn(NO3)2 (aq) + 2Ag 2AgNO3 (aq) + 2Zn (s) d. H2 (g) + Cl2 (g) HCl (g)

  7. a hint!!!! Which reaction does not involve the formation of ions.?

  8. Which of the following is not a redox reaction. Correct because…… A redox reaction involves the transfer of electrons between reactants. a. Mg (s) + 2HCl (aq) MgCl2 (aq) + H2 (g) Mg 2+ + 2H+ Mg 2+ + H2 b. CuCO3 (s) + H2SO4 (aq) CuSO4(aq) + CO2 (g) +H2O (l) 2H+ + CO32- CO2 + H2O c. Zn(NO3)2 (aq) + 2Ag 2AgNO3 (aq) + 2Zn (s) Zn 2+ + 2Ag  2Ag + + Zn Ans: d. H2 (g) + Cl2 (g) HCl (g)

  9. In order to balance this ion-equation I – to IO 3– You need to 3 a. b. c. d.

  10. a hint!!!! 1st hint Balance the oxygen by adding water. 2nd hint Balance the hydrogen by adding H+ ions. 3rd hint Balance the charges by adding electrons

  11. In order to balance this ion-equation I – to IO 3– Correct because……… 1st balance the water molecules I – + 3H2O IO 3– 2nd balance the H using H+ ions. I – + 3H2O  IO 3– + 6H+ 3rd balance the charges by adding electrons I – + 3H2O  IO 3– + 6H+ + 6e-

  12. The balanced redox equation for the two ion-equations below is (you will need to look a you data book, page 11) 4 SO42- (aq) SO32- (aq) Fe (s) Fe 3+ (aq) a.2Fe (s) + 3SO42- (aq) 2Fe 3+ (aq) + 3SO32- (aq) b. 2Fe (s) + 3SO42- (aq) + 6H+ (aq) 2Fe 3+ (aq) + 3SO32- (aq) + 3H2 (g) c. 2Fe (s) + 3SO42- (aq) + 6H+ (aq) 2Fe 3+ (aq) + 3SO32- (aq) + 3H2O (l) d. 3Fe (s) + SO42- (aq) + 6H+ (aq) Fe 3+ (aq) + SO32- (aq) + 3H2O (l)

  13. a hint!!!! 1st hint SO42-(aq) + 2H +(aq) + 2e- SO32-(aq) + H2O (l) 2nd hint Fe (s) Fe 3+(aq) + 3e-

  14. The balanced redox equation for the two ion-equations below is (you will need to look a you data book, page 11) SO42- (aq) SO32- (aq) Fe (s) Fe 3+ (aq) Correct because…… SO42-(aq) + 2H +(aq) + 2e- SO32-(aq) + H2O (l) X 3 X 2 Fe (s) Fe 3+(aq) + 3e- 3SO42-(aq) + 6H +(aq) + 2Fe(s)3SO32-(aq) + 3H2O(l) + 2Fe 3+(aq) Ans: C

  15. What colour change takes place during this reaction? 5 5 Fe 2+ (aq) + 8H+ (aq) + MnO4- (aq)  5 Fe 3+ (aq) + Mn 2+ (aq) + 4H2O(l) a. Blue to colourless b. Colourless to purple c. Colourless to blue d. Purple to colourless

  16. a hint!!!! The permanganate ion is purple.

  17. What colour change takes place during this reaction? 5 Fe 2+ (aq) + 8H+ (aq) + MnO4- (aq)  5 Fe 3+ (aq) + Mn 2+ (aq) + 4H2O(l) Correct because……….. The MnO4- (aq) ion is purple, while the Mn 2+ (aq) ion is colourless.

  18. 25 cm 3 of 0.200 mol –1 potassium permanganate was titrated against a solution of Fe 2+ ions. The concentration of Fe 2+ ions was? 6 Titration results, 20.5 cm3, 20.1 cm3 and 20.0 cm 3 5 Fe 2+ (aq) + 8H+ (aq) + MnO4- (aq)  5 Fe 3+ (aq) + Mn 2+ (aq) + 4H2O(l) a. 1.25 mol 1- b.1.24 mol 1- c. 0.250 mol 1- d. 1.00 mol 1-

  19. a hint!!!! Have you used concordant titration results?

  20. a hint!!!! n = V x C and a 5:1 ratio of mol of Fe 2+ to MnO4-

  21. V x x C x V y x C y = n y n x a hint!!!!

  22. V x x C x V y x C y = n y n x 25 cm 3 of 0.200 mol –1 potassium permanganate was titrated against a solution of Fe 2+ ions. The concentration of Fe 2+ ions was? Titration results, 20.5 cm3, 20.1 cm3 and 20.0 cm 3 5 Fe 2+ (aq) + 8H+ (aq) + MnO4- (aq)  5 Fe 3+ (aq) + Mn 2+ (aq) + 4H2O(l) Y = Fe 3+ X = MnO4- 25 x 0.200 (20.1+20.0)/2 + Y = 1 5 Ans : b.1.24 mol 1-

  23. Al Al 3+ + 3e The production of Aluminium during the electrolysis of aluminium oxide can be represented by 7 What is the quantity of electricity needed to produce 0.2 mol of Al? a. 96,500 C b. 19300 C c. 57,900 C d.193,000

  24. a hint!!!! 1st hint How many moles of electrons are needed to deposit 1 mol of Al? 2nd hint The charge on a mole of electrons is 96,500C?

  25. Al Al 3+ + 3e The production of Aluminium during the electrolysis of aluminium oxide can be represented by What is the quantity of electricity needed to produce 0.2 mol of Al? Correct because…….. To produce 1 mole of aluminium, 3 moles of electrons are needed. i.e. 96,500 C x 3 = 289500 C needed. 1 mole Al = 289500 C 0.2 mole Al = 289500 x 0.2 = 57,900C

  26. A solution of HCl is electrolysed. What current is needed to produce 4.8 l of H2 gas in 3 min 13 sec? 1 mole of gas occupies 24 l . 8 a. 20 A b. 50 A c. 100 A d. 200 A

  27. a hint!!!! Q = I x t 1st hint How many moles of hydrogen does 4.8 l represent? 2nd hint How many moles of electrons do you need to deposit 1 mol of hydrogen gas?

  28. Quantity of charge = current x time Q = I x t A solution of HCl is electrolysed. What current is needed to produce 4.8 l of H2 gas in 3 min 13 sec? 1 mole of gas occupies 24 l ? Correct because…….. 2H+(aq) + 2e- H2(g) So to produce a mole of hydrogen gas, 2 mol of electrons are needed. 4.8l = 4.8/24 mol = 0.2 mol of gas produced. 1 mol of gas would need 96500 x 2 C 0.2 mol would need (96500 x 2) x 0.2 C = 3860 C So I = Q/t = 3860 / 193 = 20 A