实验报告-pH计测定溶液的pH值及磷酸的电位滴定

1、2018年12月2日2018年12月2日药院2017级药学一小班用pH计测定溶液的pH值及磷酸的电位滴定一、实验目的1、掌握用pH计测定溶液的pH值的方法及原理。2、通过实验学会pH计仪器的使用。3、掌握电位滴定的方法及确定终点的方法。4、学会用电位滴定法测定弱酸的pKa.二、实验原理1、直接电位法测定溶液的pH，常以pH玻璃电极作为指示电极，饱和甘汞电极作为参比电极，浸入待测液中组成原电池。（-）Ag|AgCl（s）,内充液|玻璃膜|试液|KCl（饱和），HgCl（s）|Hg（+）pHs-25型酸度计使用复合电极，玻璃电极为负极，银-氯化银电极为正极（-）玻璃电极|待测溶液|银-氯化银（+）

2、在实际工作中，采用两次测量法，pHs=pHs+（Ex-Es）/0.059实验操作要求：校准一用一种标准缓冲液按pH计的使用方法校准pH计检验一用校准好了的pH计测量另一种与校准时所用缓冲溶液的pH相差3个单位左右的标准缓冲液，测量值与表中所列值相差不应大于0.1pH单位测定一用校准好了的pH计测定待测溶液的pH2、电位滴定对于容量滴定中的酸碱都能滴定，且对于一些突跃范围小，无合适指示剂，溶液浑浊，有色的酸碱，都能滴定。此外它还可测弱酸弱碱的解离常数，还可用来寻找合适指示剂或校正指示剂的终点颜色变化。磷酸为多元酸，其pKa可用电位滴定法测定当磷酸的第一个H+被滴定一半时，此时的pH即为第一步的解

3、离常数。三、实验步骤（一）1、用邻苯二甲酸氢钾pH=4.00，测定草酸三氢钾及混合磷酸盐的pH值2、用混合磷酸盐定位pH=6.88,测定硼砂及邻苯二甲酸氢钾的pH值（二）1、实验操作（1）、打开电脑上的软件，用磷酸混合溶液及邻苯二甲酸氢钾标准溶液校准pH计，保存校准数据，接着设置滴定条件，准备滴定。（2）、用10.0ml移液管吸取磷酸样品溶液10.0ml置于100ml烧杯中，加蒸馏水20ml，放入转子，调节转速，放入复合电极以及氢氧化钠滴液管。点击开始，仪器开始滴定，并自动记录实验数据。滴定结束后，停止滴定，保存数据及滴定曲线。2、数据处理，做出一阶微商曲线，算出磷酸浓度以及第一第二解离常数。

4、四、实验数据溶液pH值测定结果表邻苯二甲酸氢钾定位（pH=4）混合磷酸盐定位（pH=6.88）次数123次数123草酸三氢钾1.621.631.60邻苯二甲酸氢钾4.074.064.05混合磷酸盐6.856.866.86硼砂9.239.249.25磷酸的电位滴定数据记录体积（mL）pH值一次导数二次导数0.001.84.002.20.0844.602.2-0.025-5.3625.142.30.1853.8755.742.40.1623.5516.242.40.1662.6716.882.50.069-2.9957.532.60.2211.7508.272.80.132-3.1468.923.

5、00.235-2.4089.323.10.5071.9329.423.20.361-5.5859.523.20.6523.7339.623.30.6783.6329.723.40.8366.8299.823.40.9852.2469.873.50.852-2.6719.913.51.1145.2819.963.60.966-2.99510.013.6-0.092-21.26610.063.71.42130.42310.113.82.02412.13110.163.81.075-19.08110.213.92.42727.20510.264.13.38019.17210.314.45.49742

6、.58310.364.52.954-51.15310.414.85.43349.86810.464.92.843-52.10410.515.13.87820.81110.565.21.286-52.14410.615.32.67928.03510.665.41.691-19.89010.715.51.176-10.35010.765.4-0.431-32.34510.815.51.35435.91610.865.62.17316.48110.915.71.412-15.31810.965.7-0.201-32.43611.015.70.83120.75011.215.90.64211.3411

7、1.416.00.6169.30811.606.10.2491.33511.806.10.4073.12612.006.20.3755.21012.206.30.1190.16212.406.30.201-5.96912.656.40.4680.60712.856.40.1923.46013.006.50.297-4.65413.206.50.035-4.74513.396.60.220-1.33513.646.60.2944.51213.846.60.3284.43114.046.70.3043.15714.246.70.2153.31814.396.70.086-3.33914.596.8

8、0.074-4.06714.746.80.2924.61314.946.80.2313.72315.236.90.2582.93415.436.90.1833.08615.636.90.2673.21715.837.00.1572.16516.037.00.2603.35916.237.10.4205.94916.437.10.2503.42016.637.10.2723.38916.877.20.344-1.11317.027.20.1515.70617.227.20.2713.62217.427.20.2334.38117.627.30.3364.31017.827.30.2635.160

9、18.027.40.5125.64518.227.40.3563.71318.417.40.3454.24918.617.50.2422.63018.817.50.6175.93919.017.60.2875.45319.167.60.259-1.36619.317.70.3761.34619.567.70.4393.31819.717.80.160-5.29119.917.90.014-7.49720.108.00.037-6.69820.158.00.73213.98220.208.11.1648.70120.258.10.957-4.15820.308.10.385-11.51320.3

10、58.20.5633.57120.408.20.543-0.39520.458.20.339-4.09720.508.21.06314.54920.558.31.2473.71320.608.30.749-10.01620.658.41.2119.29820.708.51.6478.76220.758.62.34614.06320.808.71.527-16.47120.858.71.115-8.28620.908.7-0.882-40.18620.958.93.70292.22921.009.14.84923.06721.059.46.16426.45721.109.62.529-73.12

11、721.159.73.91627.90321.209.81.734-43.88921.259.91.520-4.32021.3510.02.32659.32721.4010.23.32820.14321.5010.30.652-46.80221.6010.4-0.024-16.89621.7010.51.5569.01421.7910.60.524-16.45121.8910.60.322-4.55321.9410.70.83910.40122.0410.80.572-10.69422.1910.80.9248.23522.2910.90.006-9.05522.3910.90.6016.991由数据所绘制的滴定曲线求得平均浓度为1/2(0.1029+0.1073)=0.1051mol/l由数据查得pKa1=2.3pKa2=6.9五、实验结论在pH定位为4的情况下，测得草酸三氢钾的pH为1.62,混合磷酸盐