A lvl chem qns(MCQ)

• Bigcable22

  13 Sep 10, 21:11

  

  

  

  

• wishboy

  13 Sep 10, 22:32

  14.

  k = 5.78*10^-3

  half life = ln 2 / 5.78*10^-3 = 119.92s

  no. of half lives from 1.8 to 0.225 = 3

  time taken = 119.92*3 = 360s

• UltimaOnline

  13 Sep 10, 23:17

  Wishboy is correct regarding the kinetics question.

   

  Regarding the electrochem qn, B is the correct answer. Precipitating Mg2+ out as Mg(OH)2 ppt lowers the molarity of Mg2+, thus making the oxidation potential @ anode more positive (as predicted by Le Chatelier's principle of system opposing the change). Since cell potential = reduction potential @ cathode + oxidation potential @ anode, hence cell potential becomes more positive.