环境监测做高锰酸盐指数应该注意哪些事？

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  cyf加油呦 2019-04-23 17:26:24

  <p><span style="position:relative;line-height:2em;font-size:16px;font-family:Microsoft YaHei;color: rgb(51, 51, 51);PingFang SC&quot;, &quot;Lantinghei SC&quot;, &quot;Microsoft YaHei&quot;, arial, 宋体, sans-serif, tahoma; background-color: rgb(255, 255, 255);" data-x-flag="17_26">高锰酸盐指数表示水体水质受有机污染物和还原性无机物质污染程度的一个综合指标，它是在一定条件下，以高锰酸钾为氧化剂，处理水样时所消耗的高锰酸钾的量，以氧的mg/L表示。酸性法测定高锰酸盐指数时的误差主要来源于高锰酸钾溶液的不稳定性，浓度标定不准确引入的误差和测定条件的酸度、温度控制不当以及副反应发生引入的误差。因此，要消除误差，获得一个相对的准确测定值，必须要解决好以下几个问题：</span><br style="content: &quot;&quot;; display: block; width: 705px; height: 0px; margin: 15px 0px; color: rgb(51, 51, 51); font-family: &quot;PingFang SC&quot;, &quot;Lantinghei SC&quot;, &quot;Microsoft YaHei&quot;, arial, 宋体, sans-serif, tahoma; white-space: normal; background-color: rgb(255, 255, 255);"/><span style="position:relative;line-height:2em;font-size:16px;font-family:Microsoft YaHei;color: rgb(51, 51, 51);PingFang SC&quot;, &quot;Lantinghei SC&quot;, &quot;Microsoft YaHei&quot;, arial, 宋体, sans-serif, tahoma; background-color: rgb(255, 255, 255);" data-x-flag="17_26">1配制较稳定的高锰酸钾溶液</span><br style="content: &quot;&quot;; display: block; width: 705px; height: 0px; margin: 15px 0px; color: rgb(51, 51, 51); font-family: &quot;PingFang SC&quot;, &quot;Lantinghei SC&quot;, &quot;Microsoft YaHei&quot;, arial, 宋体, sans-serif, tahoma; white-space: normal; background-color: rgb(255, 255, 255);"/><span style="position:relative;line-height:2em;font-size:16px;font-family:Microsoft YaHei;color: rgb(51, 51, 51);PingFang SC&quot;, &quot;Lantinghei SC&quot;, &quot;Microsoft YaHei&quot;, arial, 宋体, sans-serif, tahoma; background-color: rgb(255, 255, 255);" data-x-flag="17_26">纯的高锰酸钾溶液是相当稳定的，但因市售的高锰酸钾试剂常含有二氧化锰和其它杂质，如硫酸盐、氯化物和硝酸盐等，并且受蒸馏水中常含有微量还原性物质的影响，它们可与MnO4-反应而析出MnO(OH)2沉淀，MnO2和MnO(OH)2又能促进高锰酸钾溶液的分解，此外，由于KMnO4溶液能自行分解，其分解方程式如下：</span><br style="content: &quot;&quot;; display: block; width: 705px; height: 0px; margin: 15px 0px; color: rgb(51, 51, 51); font-family: &quot;PingFang SC&quot;, &quot;Lantinghei SC&quot;, &quot;Microsoft YaHei&quot;, arial, 宋体, sans-serif, tahoma; white-space: normal; background-color: rgb(255, 255, 255);"/><span style="position:relative;line-height:2em;font-size:16px;font-family:Microsoft YaHei;color: rgb(51, 51, 51);PingFang SC&quot;, &quot;Lantinghei SC&quot;, &quot;Microsoft YaHei&quot;, arial, 宋体, sans-serif, tahoma; background-color: rgb(255, 255, 255);" data-x-flag="17_26">4KMnO4+2H2O==4MnO2+4KOH+3O2↑</span><br style="content: &quot;&quot;; display: block; width: 705px; height: 0px; margin: 15px 0px; color: rgb(51, 51, 51); font-family: &quot;PingFang SC&quot;, &quot;Lantinghei SC&quot;, &quot;Microsoft YaHei&quot;, arial, 宋体, sans-serif, tahoma; white-space: normal; background-color: rgb(255, 255, 255);"/><span style="position:relative;line-height:2em;font-size:16px;font-family:Microsoft YaHei;color: rgb(51, 51, 51);PingFang SC&quot;, &quot;Lantinghei SC&quot;, &quot;Microsoft YaHei&quot;, arial, 宋体, sans-serif, tahoma; background-color: rgb(255, 255, 255);" data-x-flag="17_26">分解的速度因溶液的PH值而不同，一般在中性溶液中分解很慢，在碱性和酸性溶液中分解较快，同时有Mn2+和MnO2的存在下能加速其分解，见光分解的速度更快。因此，必须正确地配制和保存高锰酸钾溶液。</span><br style="content: &quot;&quot;; display: block; width: 705px; height: 0px; margin: 15px 0px; color: rgb(51, 51, 51); font-family: &quot;PingFang SC&quot;, &quot;Lantinghei SC&quot;, &quot;Microsoft YaHei&quot;, arial, 宋体, sans-serif, tahoma; white-space: normal; background-color: rgb(255, 255, 255);"/><span style="position:relative;line-height:2em;font-size:16px;font-family:Microsoft YaHei;color: rgb(51, 51, 51);PingFang SC&quot;, &quot;Lantinghei SC&quot;, &quot;Microsoft YaHei&quot;, arial, 宋体, sans-serif, tahoma; background-color: rgb(255, 255, 255);" data-x-flag="17_26">为了配制较稳定的KMnO4溶液，常采用下列措施：</span><br style="content: &quot;&quot;; display: block; width: 705px; height: 0px; margin: 15px 0px; color: rgb(51, 51, 51); font-family: &quot;PingFang SC&quot;, &quot;Lantinghei SC&quot;, &quot;Microsoft YaHei&quot;, arial, 宋体, sans-serif, tahoma; white-space: normal; background-color: rgb(255, 255, 255);"/><span style="position:relative;line-height:2em;font-size:16px;font-family:Microsoft YaHei;color: rgb(51, 51, 51);PingFang SC&quot;, &quot;Lantinghei SC&quot;, &quot;Microsoft YaHei&quot;, arial, 宋体, sans-serif, tahoma; background-color: rgb(255, 255, 255);" data-x-flag="17_26">（1）称取少多于理论量的KMnO4，溶解在规定体积的蒸馏水中，例如配制C（ KMnO4）=0.1mol/LKMnO4溶液1L，一般称取3.3～3.5g固体KMnO4。</span><br style="content: &quot;&quot;; display: block; width: 705px; height: 0px; margin: 15px 0px; color: rgb(51, 51, 51); font-family: &quot;PingFang SC&quot;, &quot;Lantinghei SC&quot;, &quot;Microsoft YaHei&quot;, arial, 宋体, sans-serif, tahoma; white-space: normal; background-color: rgb(255, 255, 255);"/><span style="position:relative;line-height:2em;font-size:16px;font-family:Microsoft YaHei;color: rgb(51, 51, 51);PingFang SC&quot;, &quot;Lantinghei SC&quot;, &quot;Microsoft YaHei&quot;, arial, 宋体, sans-serif, tahoma; background-color: rgb(255, 255, 255);" data-x-flag="17_26">（2）将配制好的KMnO4溶液加热至沸腾并维持微沸状态约1h，然后放置2～3d，使溶液中可能存在的还原性物质完全养花。</span><br style="content: &quot;&quot;; display: block; width: 705px; height: 0px; margin: 15px 0px; color: rgb(51, 51, 51); font-family: &quot;PingFang SC&quot;, &quot;Lantinghei SC&quot;, &quot;Microsoft YaHei&quot;, arial, 宋体, sans-serif, tahoma; white-space: normal; background-color: rgb(255, 255, 255);"/><span style="position:relative;line-height:2em;font-size:16px;font-family:Microsoft YaHei;color: rgb(51, 51, 51);PingFang SC&quot;, &quot;Lantinghei SC&quot;, &quot;Microsoft YaHei&quot;, arial, 宋体, sans-serif, tahoma; background-color: rgb(255, 255, 255);" data-x-flag="17_26">（3）用微孔玻璃漏斗过滤，除去析出的沉淀。</span><br style="content: &quot;&quot;; display: block; width: 705px; height: 0px; margin: 15px 0px; color: rgb(51, 51, 51); font-family: &quot;PingFang SC&quot;, &quot;Lantinghei SC&quot;, &quot;Microsoft YaHei&quot;, arial, 宋体, sans-serif, tahoma; white-space: normal; background-color: rgb(255, 255, 255);"/><span style="position:relative;line-height:2em;font-size:16px;font-family:Microsoft YaHei;color: rgb(51, 51, 51);PingFang SC&quot;, &quot;Lantinghei SC&quot;, &quot;Microsoft YaHei&quot;, arial, 宋体, sans-serif, tahoma; background-color: rgb(255, 255, 255);" data-x-flag="17_26">（4）将过滤后的KMnO4溶液储存于棕色试剂瓶中并存放于暗处，以待标定。</span><br style="content: &quot;&quot;; display: block; width: 705px; height: 0px; margin: 15px 0px; color: rgb(51, 51, 51); font-family: &quot;PingFang SC&quot;, &quot;Lantinghei SC&quot;, &quot;Microsoft YaHei&quot;, arial, 宋体, sans-serif, tahoma; white-space: normal; background-color: rgb(255, 255, 255);"/><span style="position:relative;line-height:2em;font-size:16px;font-family:Microsoft YaHei;color: rgb(51, 51, 51);PingFang SC&quot;, &quot;Lantinghei SC&quot;, &quot;Microsoft YaHei&quot;, arial, 宋体, sans-serif, tahoma; background-color: rgb(255, 255, 255);" data-x-flag="17_26">2 准确标定KMnO4溶液的浓度</span><br style="content: &quot;&quot;; display: block; width: 705px; height: 0px; margin: 15px 0px; color: rgb(51, 51, 51); font-family: &quot;PingFang SC&quot;, &quot;Lantinghei SC&quot;, &quot;Microsoft YaHei&quot;, arial, 宋体, sans-serif, tahoma; white-space: normal; background-color: rgb(255, 255, 255);"/><span style="position:relative;line-height:2em;font-size:16px;font-family:Microsoft YaHei;color: rgb(51, 51, 51);PingFang SC&quot;, &quot;Lantinghei SC&quot;, &quot;Microsoft YaHei&quot;, arial, 宋体, sans-serif, tahoma; background-color: rgb(255, 255, 255);" data-x-flag="17_26">标定KMnO4溶液的基准物质较多，如Na2C2O4、As2O3 、 H2C2O4•2H2O 和纯铁丝等，其中以Na2C2O4较为常用。因为它易于提纯，性质稳定，不含结晶水。其标定方法是将Na2C2O4在105～110℃烘干约2h以后，冷却至室温即可使用。在H2SO4酸性溶液中MnO4-与C2O42-的反应：</span><br style="content: &quot;&quot;; display: block; width: 705px; height: 0px; margin: 15px 0px; color: rgb(51, 51, 51); font-family: &quot;PingFang SC&quot;, &quot;Lantinghei SC&quot;, &quot;Microsoft YaHei&quot;, arial, 宋体, sans-serif, tahoma; white-space: normal; background-color: rgb(255, 255, 255);"/><span style="position:relative;line-height:2em;font-size:16px;font-family:Microsoft YaHei;color: rgb(51, 51, 51);PingFang SC&quot;, &quot;Lantinghei SC&quot;, &quot;Microsoft YaHei&quot;, arial, 宋体, sans-serif, tahoma; background-color: rgb(255, 255, 255);" data-x-flag="17_26">2MnO4-+5C2O42-+16H+==2Mn2++10CO2↑+8H2O</span><br style="content: &quot;&quot;; display: block; width: 705px; height: 0px; margin: 15px 0px; color: rgb(51, 51, 51); font-family: &quot;PingFang SC&quot;, &quot;Lantinghei SC&quot;, &quot;Microsoft YaHei&quot;, arial, 宋体, sans-serif, tahoma; white-space: normal; background-color: rgb(255, 255, 255);"/><span style="position:relative;line-height:2em;font-size:16px;font-family:Microsoft YaHei;color: rgb(51, 51, 51);PingFang SC&quot;, &quot;Lantinghei SC&quot;, &quot;Microsoft YaHei&quot;, arial, 宋体, sans-serif, tahoma; background-color: rgb(255, 255, 255);" data-x-flag="17_26">为了能使此反应定量的迅速进行，应控制好以下条件：</span><br style="content: &quot;&quot;; display: block; width: 705px; height: 0px; margin: 15px 0px; color: rgb(51, 51, 51); font-family: &quot;PingFang SC&quot;, &quot;Lantinghei SC&quot;, &quot;Microsoft YaHei&quot;, arial, 宋体, sans-serif, tahoma; white-space: normal; background-color: rgb(255, 255, 255);"/><span style="position:relative;line-height:2em;font-size:16px;font-family:Microsoft YaHei;color: rgb(51, 51, 51);PingFang SC&quot;, &quot;Lantinghei SC&quot;, &quot;Microsoft YaHei&quot;, arial, 宋体, sans-serif, tahoma; background-color: rgb(255, 255, 255);" data-x-flag="17_26">（1）温度控制：反应温度70～80℃。低于此温度或室温下反应速度极慢，温度超过90℃，H2C2O4部分分解导致标定结果偏高。</span><br style="content: &quot;&quot;; display: block; width: 705px; height: 0px; margin: 15px 0px; color: rgb(51, 51, 51); font-family: &quot;PingFang SC&quot;, &quot;Lantinghei SC&quot;, &quot;Microsoft YaHei&quot;, arial, 宋体, sans-serif, tahoma; white-space: normal; background-color: rgb(255, 255, 255);"/><span style="position:relative;line-height:2em;font-size:16px;font-family:Microsoft YaHei;color: rgb(51, 51, 51);PingFang SC&quot;, &quot;Lantinghei SC&quot;, &quot;Microsoft YaHei&quot;, arial, 宋体, sans-serif, tahoma; background-color: rgb(255, 255, 255);" data-x-flag="17_26">（2）酸度控制： 滴定应在一定酸度的H2SO4介质中进行，一般滴定开始时，溶液应为0.5～1mol/L左右，滴定终了时应为0.2～0.5mol/L左右。酸度过低，MnO4-会部分被还原成MnO2；酸度过高会促进H2C2O4分解。</span><br style="content: &quot;&quot;; display: block; width: 705px; height: 0px; margin: 15px 0px; color: rgb(51, 51, 51); font-family: &quot;PingFang SC&quot;, &quot;Lantinghei SC&quot;, &quot;Microsoft YaHei&quot;, arial, 宋体, sans-serif, tahoma; white-space: normal; background-color: rgb(255, 255, 255);"/><span style="position:relative;line-height:2em;font-size:16px;font-family:Microsoft YaHei;color: rgb(51, 51, 51);PingFang SC&quot;, &quot;Lantinghei SC&quot;, &quot;Microsoft YaHei&quot;, arial, 宋体, sans-serif, tahoma; background-color: rgb(255, 255, 255);" data-x-flag="17_26">（3）滴定速度 滴定时应待diyi滴KMnO4红色褪去之后再滴入第二滴，因为滴定反应速度极慢，只有滴入KMnO4反应生成Mn2+作为催化剂时，滴定才逐渐加快。否则再热的酸性溶液中，滴入的KMnO4来不及和C2O42-反应而发生分解：</span><br style="content: &quot;&quot;; display: block; width: 705px; height: 0px; margin: 15px 0px; color: rgb(51, 51, 51); font-family: &quot;PingFang SC&quot;, &quot;Lantinghei SC&quot;, &quot;Microsoft YaHei&quot;, arial, 宋体, sans-serif, tahoma; white-space: normal; background-color: rgb(255, 255, 255);"/><span style="position:relative;line-height:2em;font-size:16px;font-family:Microsoft YaHei;color: rgb(51, 51, 51);PingFang SC&quot;, &quot;Lantinghei SC&quot;, &quot;Microsoft YaHei&quot;, arial, 宋体, sans-serif, tahoma; background-color: rgb(255, 255, 255);" data-x-flag="17_26">4MnO4-+12H+==4Mn2++5O2↑+6H2O</span><br style="content: &quot;&quot;; display: block; width: 705px; height: 0px; margin: 15px 0px; color: rgb(51, 51, 51); font-family: &quot;PingFang SC&quot;, &quot;Lantinghei SC&quot;, &quot;Microsoft YaHei&quot;, arial, 宋体, sans-serif, tahoma; white-space: normal; background-color: rgb(255, 255, 255);"/><span style="position:relative;line-height:2em;font-size:16px;font-family:Microsoft YaHei;color: rgb(51, 51, 51);PingFang SC&quot;, &quot;Lantinghei SC&quot;, &quot;Microsoft YaHei&quot;, arial, 宋体, sans-serif, tahoma; background-color: rgb(255, 255, 255);" data-x-flag="17_26">导致标定结果偏低。</span><br style="content: &quot;&quot;; display: block; width: 705px; height: 0px; margin: 15px 0px; color: rgb(51, 51, 51); font-family: &quot;PingFang SC&quot;, &quot;Lantinghei SC&quot;, &quot;Microsoft YaHei&quot;, arial, 宋体, sans-serif, tahoma; white-space: normal; background-color: rgb(255, 255, 255);"/><span style="position:relative;line-height:2em;font-size:16px;font-family:Microsoft YaHei;color: rgb(51, 51, 51);PingFang SC&quot;, &quot;Lantinghei SC&quot;, &quot;Microsoft YaHei&quot;, arial, 宋体, sans-serif, tahoma; background-color: rgb(255, 255, 255);" data-x-flag="17_26">（4）滴定终点 KMnO4终点不太稳定，这是由于空气中还原性气体及尘埃等杂质使MnO4-缓慢分解，粉红色消失，所以经半分钟不退色即可认为已经到达滴定终点。</span><br style="content: &quot;&quot;; display: block; width: 705px; height: 0px; margin: 15px 0px; color: rgb(51, 51, 51); font-family: &quot;PingFang SC&quot;, &quot;Lantinghei SC&quot;, &quot;Microsoft YaHei&quot;, arial, 宋体, sans-serif, tahoma; white-space: normal; background-color: rgb(255, 255, 255);"/><span style="position:relative;line-height:2em;font-size:16px;font-family:Microsoft YaHei;color: rgb(51, 51, 51);PingFang SC&quot;, &quot;Lantinghei SC&quot;, &quot;Microsoft YaHei&quot;, arial, 宋体, sans-serif, tahoma; background-color: rgb(255, 255, 255);" data-x-flag="17_26">3 严格控制测定条件</span><br style="content: &quot;&quot;; display: block; width: 705px; height: 0px; margin: 15px 0px; color: rgb(51, 51, 51); font-family: &quot;PingFang SC&quot;, &quot;Lantinghei SC&quot;, &quot;Microsoft YaHei&quot;, arial, 宋体, sans-serif, tahoma; white-space: normal; background-color: rgb(255, 255, 255);"/><span style="position:relative;line-height:2em;font-size:16px;font-family:Microsoft YaHei;color: rgb(51, 51, 51);PingFang SC&quot;, &quot;Lantinghei SC&quot;, &quot;Microsoft YaHei&quot;, arial, 宋体, sans-serif, tahoma; background-color: rgb(255, 255, 255);" data-x-flag="17_26">高锰酸盐指数是一个相对的条件性指标，是在一定条件下的测定结果。其测定结果与溶液的酸度、高锰酸盐浓度、加热温度和时间有关。因此，测定时必须严格遵守操作规定，使结果具可比性。操作步骤应按《水和废水分析方法》（第4版）的规定进行。应注意以下几个问题：</span><br style="content: &quot;&quot;; display: block; width: 705px; height: 0px; margin: 15px 0px; color: rgb(51, 51, 51); font-family: &quot;PingFang SC&quot;, &quot;Lantinghei SC&quot;, &quot;Microsoft YaHei&quot;, arial, 宋体, sans-serif, tahoma; white-space: normal; background-color: rgb(255, 255, 255);"/><span style="position:relative;line-height:2em;font-size:16px;font-family:Microsoft YaHei;color: rgb(51, 51, 51);PingFang SC&quot;, &quot;Lantinghei SC&quot;, &quot;Microsoft YaHei&quot;, arial, 宋体, sans-serif, tahoma; background-color: rgb(255, 255, 255);" data-x-flag="17_26">(1) 应先标定好0.1mol/L KMnO4(1/5KMnO4)准确浓度，再根据稀释公式把浓度调节到0.01000—0.009600mol/L范围内，以减小误差。</span><br style="content: &quot;&quot;; display: block; width: 705px; height: 0px; margin: 15px 0px; color: rgb(51, 51, 51); font-family: &quot;PingFang SC&quot;, &quot;Lantinghei SC&quot;, &quot;Microsoft YaHei&quot;, arial, 宋体, sans-serif, tahoma; white-space: normal; background-color: rgb(255, 255, 255);"/><span style="position:relative;line-height:2em;font-size:16px;font-family:Microsoft YaHei;color: rgb(51, 51, 51);PingFang SC&quot;, &quot;Lantinghei SC&quot;, &quot;Microsoft YaHei&quot;, arial, 宋体, sans-serif, tahoma; background-color: rgb(255, 255, 255);" data-x-flag="17_26">(2) 加入10.00ml的0.01mol/LKMnO4和0.01mol/LNa2C2O4时均应用A级胖肚移液管，这样既快又准。</span></p>

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