完成下列反应的化学方程式，并回答有关问题．
（1）铁在纯氧中燃烧______，反应类型______；
（2）高炉炼铁的主要反应______，被还原的物质______；
（3）滴加少量硝酸银溶液到氯化钠溶液中______；反应现象______．
（1）铁在纯氧中燃烧，生成四氧化三铁，方程式为3Fe+2O2
Fe3O4，反应特点是“多变一”，属于化合反应． 点燃 .
（2）高炉炼铁的还原剂是CO，铁矿石常用赤铁矿，其主要成分是氧化铁，方程式为3CO+Fe2O3
2Fe+3CO2；被还原的物质是Fe2O3． 高温 .
（3）根据置换反应，相互交换成分的特点，可判断其产物为AgCl沉淀和 NaNO3，方程式为NaCl+AgNO3═AgCl↓+NaNO3．
故答案为：（1）3Fe+2O2
Fe3O4；化合反应．（2）3CO+Fe2O3 点燃 .
2Fe+3CO2；Fe2O3．（3）NaCl+AgNO3═AgCl↓+NaNO3；有白色沉淀生成． 高温 .
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