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<h2 style="text-indent:21.0pt;"><span style="font-size:14.0pt;font-family:仿宋_GB2312;">方法原理</span></h2>
<p style="text-indent:21.0pt;"><span style="font-size:14.0pt;">以玻璃电极为指示电级，饱和甘汞电极为参比电级组成电池，在<span>25</span>℃理想条件下，氢离子活度变化<span>10</span>倍，使电动势偏移<span>59.15mv</span>。许多<span>pH</span>计上有温度补偿装置，以使校正温度差异，用于常规水样监测可准确和再现至<span>0.1pH</span>单位，较精密的仪器可准确到<span>0.10pH</span>。为了提高测定的准确度，较准仪器时应选用的标准缓冲溶液的<span>pH</span>值应与水样的<span>pH</span>值接近。</span></p>
<h2 style="text-indent:21.0pt;"><span style="font-size:14.0pt;">仪器</span></h2>
<p style="margin-left:37.2pt;text-indent:-16.2pt;"><span style="font-size: "><span>1、<span> </span></span></span><span style="font-size:14.0pt;font-family:仿宋_GB2312;">各种型号的<span>pH</span>计或离子活度计。</span></p>
<p style="margin-left:37.2pt;text-indent:-16.2pt;"><span style="font-size: "><span>2、<span> </span></span></span><span style="font-size:14.0pt;font-family:仿宋_GB2312;">玻璃电极。</span></p>
<p style="margin-left:37.2pt;text-indent:-16.2pt;"><span style="font-size: "><span>3、<span> </span></span></span><span style="font-size:14.0pt;font-family:仿宋_GB2312;">甘汞电极或银<span>-</span>氯化银电极。</span></p>
<p style="margin-left:37.2pt;text-indent:-16.2pt;"><span style="font-size: "><span>4、<span> </span></span></span><span style="font-size:14.0pt;font-family:仿宋_GB2312;">磁力搅拌器。</span></p>
<p style="margin-left:37.2pt;text-indent:-16.2pt;"><span style="font-size: "><span>5、<span> </span></span></span><span style="font-size:14.0pt;">50ml</span><span style="font-size:14.0pt;font-family: 仿宋_GB2312">烧杯，最好是聚乙烯或聚四氟乙烯烧杯。</span></p>
<h2 style="margin-left:21.0pt;"><span style="font-size:14.0pt;">试剂</span></h2>
<p style="text-indent:21.0pt;"><span style="font-size:14.0pt;">用于校准仪器的标准缓冲溶液<span><span> </span></span>数量称取试剂，溶于水中，在容量瓶内定容至<span>1000ml</span>。水的电导率应低于<span>2</span>ч<span>S/cm</span>，临用前煮沸数分钟，赶除二氧化碳，冷却，取<span>50ml</span>冷却的水，加<span>1</span>滴饱和和氯化钾溶液，如<span>pH</span>在<span>6-7</span>之间即可用于配制各种标准缓冲溶液。</span></p>
<p align="center" style="text-align:center;"><span style="font-size:14.0pt;font-family:仿宋_GB2312;"> </span></p>
<p align="center" style="text-align:center;"><span style="font-size:14.0pt;font-family:仿宋_GB2312;">表<span>3<span> </span>pH</span>标准溶液的配制</span></p>
| <p align="center" style="text-align:center;"><span style="font-size:14.0pt;font-family:仿宋_GB2312;">标<span><span> </span></span>准<span><span> </span></span>物<span><span> </span></span>质</span></p> | <p align="center" style="text-align:center;"><span style="font-size:14.0pt;font-family:仿宋_GB2312;">pH</span></p> <p align="center" style="text-align:center;"><span style="font-size:14.0pt;font-family:仿宋_GB2312;">（<span>25</span>℃）</span></p> | <p align="center" style="text-align:center;"><span style="font-size:14.0pt;font-family:仿宋_GB2312;">每<span>1000ml</span>水溶液中所含试剂的</span></p> <p align="center" style="text-align:center;"><span style="font-size:14.0pt;font-family:仿宋_GB2312;">质量（<span>25</span>℃）</span></p> |
| <p><span style="font-size:14.0pt;font-family:仿宋_GB2312;">基本标准</span></p> | <p><span style="font-size:14.0pt;font-family:仿宋_GB2312;"> </span></p> | <p><span style="font-size:14.0pt;font-family:仿宋_GB2312;"> </span></p> |
| <p><span style="font-size:14.0pt;font-family:仿宋_GB2312;">酒石酸氢钾（<span>25</span>℃饱和）</span></p> | <p><span style="font-size:14.0pt;font-family:仿宋_GB2312;">3.557</span></p> | <p><span style="font-size:14.0pt;font-family:仿宋_GB2312;">6.4gKHC4H4O3</span><span style="font-size:14.0pt;font-family:仿宋_GB2312;">⑴</span></p> |
| <p><span style="font-size:14.0pt;font-family:仿宋_GB2312;">柠檬酸二氢钾</span></p> | <p><span style="font-size:14.0pt;font-family:仿宋_GB2312;">3.776</span></p> | <p><span style="font-size:14.0pt;font-family:仿宋_GB2312;">11.41gKH2C8H5O7</span></p> |
| <p><span style="font-size:14.0pt;font-family:仿宋_GB2312;">邻苯二甲酸氢甲</span></p> | <p><span style="font-size:14.0pt;font-family:仿宋_GB2312;">4.008</span></p> | <p><span style="font-size:14.0pt;font-family:仿宋_GB2312;">10.12gKHC8H4O4</span></p> |
| <p><span style="font-size:14.0pt;font-family:仿宋_GB2312;">磷酸二氢钾<span>+</span>磷酸氢二钠</span></p> | <p><span style="font-size:14.0pt;font-family:仿宋_GB2312;">6.865</span></p> | <p><span style="font-size:14.0pt;font-family:仿宋_GB2312;">3.388gKH2PO4</span><span style="font-size:14.0pt;font-family:仿宋_GB2312;">⑵</span><span style="font-size:14.0pt;font-family:仿宋_GB2312;">+3.533gNa2HPO4</span></p> |
| <p><span style="font-size:14.0pt;font-family:仿宋_GB2312;">磷酸二氢钾<span>+</span>磷酸氢二钠</span></p> | <p><span style="font-size:14.0pt;font-family:仿宋_GB2312;">7.413</span></p> | <p><span style="font-size:14.0pt;font-family:仿宋_GB2312;">1.179gKH2PO4</span><span style="font-size:14.0pt;font-family:仿宋_GB2312;">⑵</span><span style="font-size:14.0pt;font-family:仿宋_GB2312;">+4.302gNa2HPO4(2,3)</span></p> |
| <p><span style="font-size:14.0pt;font-family:仿宋_GB2312;">四硼酸钠</span></p> | <p><span style="font-size:14.0pt;font-family:仿宋_GB2312;">9.180</span></p> | <p><span style="font-size:14.0pt;font-family:仿宋_GB2312;">3.80gNa2B4O7</span><span style="font-size:14.0pt;font-family:仿宋_GB2312;">·<span>10H2O(3)</span></span></p> |
| <p><span style="font-size:14.0pt;font-family:仿宋_GB2312;">碳酸氢钠<span>+</span>碳酸钠</span></p> | <p><span style="font-size:14.0pt;font-family:仿宋_GB2312;">10.012</span></p> | <p><span style="font-size:14.0pt;font-family:仿宋_GB2312;">2.92gNaHCO3+2.640gNa2CO3</span></p> |
| <p><span style="font-size:14.0pt;font-family:仿宋_GB2312;">辅助标准</span></p> | <p><span style="font-size:14.0pt;font-family:仿宋_GB2312;"> </span></p> | <p><span style="font-size:14.0pt;font-family:仿宋_GB2312;"> </span></p> |
| <p><span style="font-size:14.0pt;font-family:仿宋_GB2312;">二水合四草酸钾</span></p> | <p><span style="font-size:14.0pt;font-family:仿宋_GB2312;">1.679</span></p> | <p><span style="font-size:14.0pt;font-family:仿宋_GB2312;">12.61gKH3C4O3</span><span style="font-size:14.0pt;font-family:仿宋_GB2312;">·<span>2H2O</span>⑷</span></p> |
| <p><span style="font-size:14.0pt;font-family:仿宋_GB2312;">氢氧化钙（<span>25</span>℃饱和）</span></p> | <p><span style="font-size:14.0pt;font-family:仿宋_GB2312;">12.454</span></p> | <p><span style="font-size:14.0pt;font-family:仿宋_GB2312;">1.5gCa(OH)2</span><span style="font-size:14.0pt;font-family:仿宋_GB2312;">⑴</span></p> |
<p><span style="font-size:14.0pt;font-family:仿宋_GB2312;">注：⑴近似溶解度；⑵在<span>110~130<span><span>℃</span></span><span>烘干2</span></span>小时；⑶用新煮沸过并冷却的无二氧化碳水；</span></p>
<p style="text-indent:21.0pt;"><span style="font-size:14.0pt;">⑷烘干温度不可超出<span>60</span>℃。</span></p>
<h2 style="text-indent:21.0pt;"><span style="font-size:14.0pt;">步骤</span></h2>
<p style="text-indent:21.0pt;"><span style="font-size:14.0pt;font-family:仿宋_GB2312;">1</span><span style="font-size: ">、按照仪器使用说明书准备。</span></p>
<p style="text-indent:21.0pt;"><span style="font-size:14.0pt;font-family:仿宋_GB2312;">2</span><span style="font-size: ">、将水样与标准溶液调到同一温度，记录测定温度，把仪器温度补偿旋钮调至该温度处。选用与水样<span>pH</span>值相差不超过<span>2</span>个<span>pH</span>单位的标准溶液校准仪器。从第一个标准溶液中取出两个电极，彻底冲洗，并用滤纸吸干。再浸入第<span>2</span>个标准溶液中，共<span>pH</span>值约与前一个相差<span>3</span>个<span>pH</span>单位。如测定值与第二个标准溶液<span>pH</span>值之差大于<span>0.1pH</span>值时，就要检查仪器、电极或标准溶液是否有问题。当三者无异常情况时方可测定水样。</span></p>
<p style="text-indent:21.0pt;"><span style="font-size:14.0pt;font-family:仿宋_GB2312;">3</span><span style="font-size: ">、水样测定：先用水仔细冲洗两个电极，再用水样冲洗，然后将电极浸入水样水中，小心搅拌或摇动使其均匀，待读数稳定后记录<span>pH</span>值。</span></p>
<h2 style="text-indent:21.0pt;"><span style="font-size:14.0pt;">注意事项</span></h2>
<p style="text-indent:21.0pt;"><span style="font-size:14.0pt;font-family:仿宋_GB2312;">1</span><span style="font-size: ">、玻璃电极在使用前应在蒸馏水中浸泡<span>24</span>小时以上。用毕，冲洗干净，浸泡在水中。</span></p>
<p style="text-indent:21.0pt;"><span style="font-size:14.0pt;font-family:仿宋_GB2312;">2</span><span style="font-size: ">、测定时，玻璃电极在球泡应全部浸入溶液中，使它稍高于甘汞电极的陶瓷芯端，以免搅拌时碰破。</span></p>
<p style="text-indent:21.0pt;"><span style="font-size:14.0pt;font-family:仿宋_GB2312;">3</span><span style="font-size: ">、玻璃电极的内电极与球泡之间以及甘汞电极的内电极与陶瓷芯之间不可存在气泡，以防断路。</span></p>
<p style="text-indent:21.0pt;"><span style="font-size:14.0pt;font-family:仿宋_GB2312;">4</span><span style="font-size: ">、甘汞电极的饱和和氯化钾液面必须高于汞体，并应有适量氯化钾晶体存在，以保证氯化钾溶液的饱和。使用前必须先拔掉上孔胶塞。</span></p>
<p style="text-indent:21.0pt;"><span style="font-size:14.0pt;font-family:仿宋_GB2312;">5</span><span style="font-size: ">、为防止空气中二氧化碳溶入或水样水二氧化碳逸失，测定前不宜提前打开水样瓶塞。</span></p>
<p style="text-indent:21.0pt;"><span style="font-size:14.0pt;font-family:仿宋_GB2312;">6</span><span style="font-size: ">、玻璃电极球泡受污染时，可用稀盐酸溶解无盐结垢，用丙酮除去油污（但不能用无水乙醇）。按上述方法处理的电极应在水中浸泡一昼夜再使用。</span></p>
<span style="font-size:14.0pt;font-family:仿宋_GB2312;" new"="" times=""> 7</span><span style="font-size:14.0pt;font-family:仿宋_GB2312;">、注意电极的出厂日期，存放时间过长的电极性能将变劣。</span>
