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CLASS PRACTICE

CLASS PRACTICE. a. Is chlorine an acidic or an alkaline gas?. 12. acidic. b. What two properties made chlorine a dangerous gas in World War I?. Poisonous. Density (it stayed at ground level rather than rising). CLASS PRACTICE. c. Some chlorine water is left in sunlight for a long time.

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CLASS PRACTICE

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  1. CLASS PRACTICE a. Is chlorine an acidic or an alkaline gas? 12 acidic b. What two properties made chlorine a dangerous gas in World War I? Poisonous. Density (it stayed at ground level rather than rising).

  2. CLASS PRACTICE c. Some chlorine water is left in sunlight for a long time. What solution remains? hydrochloric acid

  3. CLASS PRACTICE 13 Chlorine water consists of four types of particles. Which particles explain why chlorine water: a. smells of chlorine? Cl2(g) b. turns litmus red? HCl(aq), or H+(aq)

  4. CLASS PRACTICE c. bleaches? HOCl(aq) or OCl-(aq) End

  5. CLASS PRACTICE 14 Chlorine water reacts with an aqueous solution of potassium iodide. a. What colour changes occur? Solution becomes yellow / brown as iodine forms.

  6. CLASS PRACTICE b. What is: (i). oxidized; and iodide ions, I-(aq) (ii). reduced? chlorine, Cl2(aq)

  7. CLASS PRACTICE c. Write the overall ionic equation for the reaction. Cl2(aq) + 2I-(aq)  2Cl-(aq) + I2(aq)

  8. CLASS PRACTICE 15 Explain the redox reactions above using oxidation numbers. Chlorine is reduced - ON decreases from 0 to -1. Bromide/iodide ions are oxidized - ON increases from -1 to 0. End

  9. CLASS PRACTICE 16 Why do articles bleached with chlorine bleach not return to their original colours? This involves the removal of oxygen from the dye and cannot occur by exposure to the air. (Cf. equation p 223). End

  10. CLASS PRACTICE 17 Write complete ionic equations for the reaction of sulphur dioxide solution with: a. iron(III) ions 2Fe3+(aq) + SO32-(aq) + H2O(l)  2Fe2+(aq) + SO42-(aq) + 2H+(aq)

  11. CLASS PRACTICE b. acidified potassium permanganate solution 5SO32-(aq) + 2MnO4-(aq) + 6H+(aq)  5SO42-(aq) + 2Mn2+(aq) + 3H2O(l) c. bromine water Br2(aq) + SO32-(aq) + H2O(l)  2Br-(aq) + SO42-(aq) + 2H+(aq)

  12. CLASS PRACTICE 18 Sulphur dioxide reacts with acidified potassium dichromate solution (as in Fig. 21.20). a. What ion has: (i). the orange colour; and dichromate ion, Cr2O72-(aq)

  13. CLASS PRACTICE (ii). the green colour? chromium(III) ion, Cr3+(aq)

  14. CLASS PRACTICE b. Write the ionic half equation for the colour change. Cr2O72+(aq) + 14H+(aq) + 6e- 2Cr3+(aq) + 7H2O(l) c. Write the ionic equation for the overall redox reaction. 3SO32-(aq) + Cr2O72-(aq) + 8H+(aq)  3SO42-(aq) + 2Cr3+(aq) + 4H2O(l) End

  15. CLASS PRACTICE 19 If household bleach splashes onto your face what should you do? Bleach is an irritant to eyes and skin. Wash thoroughly with water. End

  16. CLASS PRACTICE 20 In summer, the amount of chlorine in drinking water is increased (to 1.0 mg/dm3). Suggest a reason why. Chlorine water decomposes more rapidly in warm water and sunlight (see p 221).

  17. CLASS PRACTICE 21 Calcium hydroxide neutralizes the hydrochloric acid in water. a. Write the word equation for this reaction. calcium hydroxide + hydrochloric acid  calcium chloride + water b. Write the chemical equation. Ca(OH)2(aq) + 2HCl(aq)  CaCl2(aq) + 2H2O(l)

  18. CLASS PRACTICE 22 One dm3 of drinking water contains 0.8 mg of chlorine Cl2. a. Calculate the number of moles of chlorine in 1 dm3. 0.0000113 mol b. What volume of chlorine gas is dissolved (measured at room temperature and pressure)? 0.27 cm3

  19. CLASS PRACTICE c. Is this a large amount of chlorine? extremely small

  20. CLASS PRACTICE 23 Swimming pool water has a pH of about 7 and not 8. Why? Neutral, so that the water does not irritate swimmers’ eyes. End

  21. CLASS PRACTICE 24 Suggest other questions we should consider before setting up a chlorine plant. (Similar to earlier questions, e.g. p 199, Class practice 34.)

  22. CLASS PRACTICE a. Name other products of the electrolysis of brine. 25 b. What are the hazards of these products? Hydrogen gas - explosive. Sodium hydroxide solution - corrosive.

  23. CLASS PRACTICE 26 Suggest reasons why Hong Kong should not build a large chlorine plant. • E.g. • Plant would be too close to populated areas. • Chlorine is highly toxic. • Transporting gaseous or liquid chlorine would be hazardous. • HK could not use most of the chlorine. • Very large quantities of electricity would be needed. End

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