题目

  I live on the twelfth floor of a building. One afternoon I was coming home from a friend’s house. It was just after four o’clock. I got quickly into the lift and pressed Button (按钮) 12. The lift started to go up, but very slowly. And then, half way up, it suddenly stopped between two floors. I couldn’t understand it. I pressed all the buttons from 1 to 14. I called for help very loudly. But nobody answered. Then suddenly the light went out, and I was alone in the dark. I started to cry and beat the walls of the lift. I cried and cried until I had no voice left. Then, I fel氧化还原反应是中学化学中常见且重要的一类反应，回答下列问题：(1)下列金属单质参加的化学反应都是氧化还原反应，都是金属失电子。①相同质量的钠分别与氧气反应，全部生成氧化钠和全部生成过氧化钠两种情况下转移的电子数目之比是________；②分别取W克钠、铁、铝与足量的盐酸反应，失去电子的物质的量之比是________；③分别取含0.1mol H2SO4的稀硫酸和含0.1mol NaOH的氢氧化钠溶液于两支试管中，分别加入足量的铝粉充分反应，产生氢气 (同温同压下)的体积之比是________。(2)某氧化还原反应的反应物和生成物共五种物质：O2、H2CrO4、Cr(OH)3、H2O、H2O2。已知该反应中H2O2转化为氧气。①该反应中的还原剂是____________；②如果化学方程式中Cr(OH)3和H2O2的物质的量之比为2:3，写出该反应的化学方程式，并标出电子转移的方向和数目_________________；③如果反应中转移了3a mol电子，则产生的气体在标准状况下体积为______L。