【简答题】七选五 People have been and flying kites for about 2,000 years.____ 1 ____Some historians believe that the ancient Chinese may have started kite flying 2,000 years ago.It is still a popular hobby ...
【简答题】实验室常利用甲醛法测定(NH 4 ) 2 SO 4 样品中氮的质量分数,其反应原理为:4NH 4 + +6HCHO═3H + +6H 2 O+(CH 2 ) 6 N 4 H + [滴定时,1mol(CH 2 ) 6 N 4 H + 与1molH + 相当],然后用NaOH标准溶液滴定反应生成的酸.某兴趣小组用甲醛法进行了如下实验: 步骤I:称取样品1.500g. 步骤Ⅱ:将样品溶解后,完全转移到2...
【简答题】用甲醛法测定试剂(NH4)2SO4中NH4+的质量分数时,若试剂中含有少量游离酸,甲醛中含有少量甲酸(HCOOH),应如何处理?滴定过程中溶液颜色如何变化?
【单选题】以下哪一结构不是在肱骨尺侧神经血管鞘里走行
【单选题】用甲醛法测定ω[(NH4)2 SO4]>98%的肥田粉{Mr[(NH4)2 SO4]=32)中NH4+含量时,若将试样溶解后用250 mL容量瓶定容,用25 mL移液管吸取三份溶液作平行测定,分别用0.2 mol·L-1NaOH溶液滴定,则应称取多少克试样?( )。
【单选题】心理的自然机制和心理“事实”主要依靠什么路径寻求解决:
【简答题】PASSAGE THREE Three years ago, Joseph J. Ellis, one of the most widely read American historians, ran into a career cr of his own strange devising. Just months after his book, Founding Brothers: Th...