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<h2 style="text-indent:21.0pt;"><span style="font-size:14.0pt;font-family:仿宋_GB2312;">1</span><span style="font-size:14.0pt;">、原理</span></h2>
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<p style="text-indent:21.0pt;"><span style="font-size:14.0pt;">水样中加入硫酸锰和碱性碘化钙，水中溶解氧将低价锰氧化成高价锰，生成四价锰的氢氧化物棕色沉淀、加酸后，氢氧化物沉淀溶解并与碘离子反应而释出游离碘，以淀粉作指示剂，用硫代硫酸钠滴定释出碘，可计算溶解氧的含量。</span></p>
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<h2 style="text-indent:21.0pt;"><span style="font-size:14.0pt;font-family:仿宋_GB2312;">2</span><span style="font-size:14.0pt;">、仪器</span></h2>
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<p style="text-indent:21.0pt;"><span style="font-size:14.0pt;font-family:仿宋_GB2312;">250-300ml</span><span style="font-size: font-family:仿宋_GB2312;">溶解氧瓶。</span></p>
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<h2 style="text-indent:21.0pt;"><span style="font-size:14.0pt;font-family:仿宋_GB2312;">3</span><span style="font-size:14.0pt;">、试剂</span></h2>
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<p style="text-indent:21.0pt;"><span style="font-size:14.0pt;">⑴<span><span> </span></span>硫酸锰溶液：称取<span>480g</span>硫酸锰（<span>MnSO4</span>·<span>4H2O</span>）或<span>364g</span>（<span> MnSO4</span>·<span>H2O</span>）溶于水，用水稀释至<span>1000ml</span>。此溶液加至酸化过的碘化钾溶液中，遇淀粉不得产生蓝色。</span></p>
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<p style="text-indent:21.0pt;"><span style="font-size:14.0pt;">⑵<span><span> </span></span>碱性碘化钾溶液：称取<span>500g</span>碘化钾（或<span>135gNal</span>）溶于<span>200ml</span>水中，待氢氧化钠溶液冷却后，将两溶液合并，混匀，用水稀释至<span>1000ml</span>。如有沉淀，则放置过夜后，倾出上清液，贮于棕色瓶中。用橡皮塞塞紧，避光保存。此溶液酸化后，遇淀粉不应产生蓝色。</span></p>
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<p style="text-indent:21.0pt;"><span style="font-size:14.0pt;">⑶<span><span> </span>1+5</span>硫酸溶液。</span></p>
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<p style="text-indent:21.0pt;"><span style="font-size:14.0pt;">⑷<span><span> </span>1%</span>（<span>m/V</span>）淀粉溶液：称取<span>1g</span>可溶笥淀粉，用少量水调成糊状，再用刚煮沸的水冲稀至<span>100ml</span>，冷却后，加入<span>0.1g</span>水杨酸或<span> 0.4g</span>氯化锌防腐。</span></p>
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<p style="text-indent:21.0pt;"><span style="font-size:14.0pt;">⑸<span><span> </span>0.20500mol(1/6K2Cr2O7)</span>重铬酸钾标准溶液：称取于<span>105~110<span><span>℃</span></span><span>烘干2</span></span>小时并冷却为重铬酸钾<span>1.2258g</span>，溶于水，移入<span>1000ml</span>容量瓶中，用水稀释至标线，摇匀。</span></p>
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<p style="text-indent:21.0pt;"><span style="font-size:14.0pt;">⑹<span><span> </span></span>：称取<span>6.2g</span>硫代硫酸钠（<span>Na2S2O3</span>·<span>5H2O</span>）溶于煮沸放冷的水中，加入<span>0.2g</span>碳酸钠，用水稀释至<span>1000ml</span>。贮于棕色瓶中，使用前用<span>0.02501mol/L</span>重铬酸钾标准溶液标定，标定方法如下：</span></p>
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<p style="text-indent:21.0pt;"><span style="font-size:14.0pt;">在<span>250ml</span>碘量瓶中，加入<span>100ml</span>水和<span>1g</span>碘化钾，加入<span> 10ml0.02500mol/L</span>重铬酸钾标准溶液、<span>5ml1+5</span>硫酸溶液密塞，摇匀。于暗处静置<span>5min</span>后，用待标定的硫代硫酸钠溶液滴定至溶液呈淡黄色，加入<span>1ml</span>淀粉溶液，继续滴定至蓝色刚好褪去为止，记录用量。</span></p>
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<p style="none"><span style="font-size:14.0pt;font-family:仿宋_GB2312;">式中，<span>M</span>——硫代硫酸钠溶液的浓度（<span>mol/L</span>）；<span>V</span>——滴定时消耗硫代硫酸钠溶液的体积（<span>ml</span>）。</span></p>
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<p style="text-indent:21.0pt;"><span style="font-size:14.0pt;">⑺<span><span> </span></span>硫酸，ρ<span>=1.84</span>。</span></p>
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<h2 style="text-indent:21.0pt;"><span style="font-size:14.0pt;font-family:仿宋_GB2312;">4</span><span style="font-size:14.0pt;">、步骤</span></h2>
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<p style="text-indent:21.0pt;"><span style="font-size:14.0pt;font-family:仿宋_GB2312;">1</span><span style="font-size:14.0pt;font-family:仿宋_GB2312;">、溶解氧的固定</span></p>
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<p style="text-indent:21.0pt;"><span style="font-size:14.0pt;">用吸管插入溶解氧瓶的液面下，加入<span>1ml</span>硫酸锰溶液、<span>2ml</span>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。</span></p>
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<p style="text-indent:21.0pt;"><span style="font-size:14.0pt;font-family:仿宋_GB2312;">2</span><span style="font-size:14.0pt;font-family:仿宋_GB2312;">、析出碘</span></p>
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<p style="text-indent:21.0pt;"><span style="font-size:14.0pt;">轻轻打开瓶塞，立即用吸管插入液面下加入<span>2.0ml</span>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<span>5min</span>。</span></p>
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<p style="text-indent:21.0pt;"><span style="font-size:14.0pt;font-family:仿宋_GB2312;">3</span><span style="font-size:14.0pt;font-family:仿宋_GB2312;">、滴定</span></p>
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<p style="text-indent:21.0pt;"><span style="font-size:14.0pt;">吸取<span>100ml</span>上述溶液于<span>250ml</span>锥形瓶中，用硫代硫酸钠溶液滴定至溶液呈淡黄色，加入<span>1ml</span>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。</span></p>
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<p style="text-indent:21.0pt;"><span style="font-size:14.0pt;font-family:仿宋_GB2312;">4</span><span style="font-size:14.0pt;font-family:仿宋_GB2312;">、计算</span></p>
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<span style="font-size:14.0pt;font-family:仿宋_GB2312;">式中，<span>M</span>——硫代硫酸钠溶液浓度（<span>mol/L</span>）；<span>V</span>——滴定时消耗硫代硫酸钠溶液体积（<span>ml</span>）。</span>
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