水中溶解氧含量的测定.ppt
Sino-Dutch Demonstration Researcher and Training Centre for Water Treatment,水中溶解氧含量的测定,中国环境管理干部学院环境技术研究与实验中心,Sino-Dutch Demonstration Researcher and Training Centre for Water Treatment,一、概 述,1、测定溶解氧的原因:,通过测定DO判断水体是否受到污染 是活性污泥处理系统的重要监控指标 为测定BOD5打基础,Sino-Dutch Demonstration Researcher and Training Centre for Water Treatment,2、测定方法的选择,碘量法 修正法碘量法 膜电极法,清洁水可直接采用碘量法测定,Sino-Dutch Demonstration Researcher and Training Centre for Water Treatment,2、测定方法的选择,碘量法 修正法碘量法 膜电极法,Sino-Dutch Demonstration Researcher and Training Centre for Water Treatment,2、测定方法的选择,碘量法 修正法碘量法 膜电极法,根据分子氧透过薄膜的扩散速率来测定水中溶解氧。方法简便、快速,干扰少,可用于现场测定。,Sino-Dutch Demonstration Researcher and Training Centre for Water Treatment,二、试验目的,(1)熟悉碘量法测定水中溶解氧的原理及过程(2)掌握滴定管的使用(3)熟练掌握滴定终点的控制,Sino-Dutch Demonstration Researcher and Training Centre for Water Treatment,三、碘量法原理,(白色沉淀),(棕色沉淀),Sino-Dutch Demonstration Researcher and Training Centre for Water Treatment,四、试验步骤,1、取样水样常采集到溶解氧瓶中,注意不要在瓶中留有气泡。,Sino-Dutch Demonstration Researcher and Training Centre for Water Treatment,四、试验步骤,1、取样水样常采集到溶解氧瓶中,注意不要在瓶中留有气泡。,2、固定将吸管插入液面下,加入1ml硫酸锰溶液、2ml碱性碘化钾溶液,盖好瓶塞,颠倒混合数次,静置。待棕色沉淀物降至瓶内一半时,再颠倒混合一次,待沉淀物下降到瓶底。一般在取样现场固定。,Sino-Dutch Demonstration Researcher and Training Centre for Water Treatment,3、析出碘轻轻打开瓶塞,立即用吸管插入液面下加入2.0 ml硫酸。小心盖好瓶塞,颠倒混合摇匀,至沉淀物全部溶解为止,放置暗处5min。4、滴定 吸取100.0ml上述溶液于250ml锥形瓶中用硫代硫酸钠溶液滴定至溶液呈淡黄色,加入1ml淀粉溶液,继续滴定至蓝色刚好褪去为止,记录硫代硫酸钠溶液用量。,Sino-Dutch Demonstration Researcher and Training Centre for Water Treatment,5、计算式中:M硫代硫酸钠溶液浓度(mol/L);V滴定时消耗硫代硫酸钠溶液体积(ml)。,Sino-Dutch Demonstration Researcher and Training Centre for Water Treatment,6、标定硫代硫酸钠,硫代硫酸钠不稳定,在放置过程中Na2S2O3浓度会发生改变,故每次用时应进行标定,以确定其当前浓度。,Sino-Dutch Demonstration Researcher and Training Centre for Water Treatment,6、标定硫代硫酸钠250ml碘量瓶+100ml蒸馏水+1g KI+10.00ml,0.025mol/l重铬酸钾 5ml(15)硫酸 用Na2S2O3滴定到淡黄色 1ml淀粉溶液继续滴定至蓝色刚好褪去为止,记录硫代硫酸钠溶液用量。,摇匀,放置暗处5min,Sino-Dutch Demonstration Researcher and Training Centre for Water Treatment,计算:式中,V滴定时消耗硫代硫酸钠溶液体积(ml),Sino-Dutch Demonstration Researcher and Training Centre for Water Treatment,五、注意事项,(1)如果水样中含有氧化性物质,应预先于水样中加入硫代硫酸钠去除:用两个溶解氧瓶各取一瓶水样,在其中一瓶加入5ml 1+5硫酸和1g碘化钾,摇匀,此时游离出碘。以淀粉作指示剂,用硫代硫酸钠溶液滴定至蓝色刚褪,记下用量。于另一瓶水样中,加入同样量的硫代硫酸钠溶液,摇匀后,按操作步骤测定。(2)如果水样呈强酸性或强碱性,可用氢氧化钠或硫酸溶液调至中性后测定。,Sino-Dutch Demonstration Researcher and Training Centre for Water Treatment,六、思考题,(1)取水样时溶解氧瓶内为什么不能含有气泡?(2)加硫酸时为什么要插入液面以下?(3)当碘析出时为什么把溶解氧瓶放置暗处5min?,