實(shí)驗(yàn)報(bào)告-pH計(jì)測(cè)定溶液的pH值及磷酸的電位滴定

1、2018年12月2日2018年12月2日藥院2017級(jí)藥學(xué)一小班用pH計(jì)測(cè)定溶液的pH值及磷酸的電位滴定一、實(shí)驗(yàn)?zāi)康?、掌握用pH計(jì)測(cè)定溶液的pH值的方法及原理。2、通過(guò)實(shí)驗(yàn)學(xué)會(huì)pH計(jì)儀器的使用。3、掌握電位滴定的方法及確定終點(diǎn)的方法。4、學(xué)會(huì)用電位滴定法測(cè)定弱酸的pKa.二、實(shí)驗(yàn)原理1、直接電位法測(cè)定溶液的pH，常以pH玻璃電極作為指示電極，飽和甘汞電極作為參比電極，浸入待測(cè)液中組成原電池。（-）Ag|AgCl（s）,內(nèi)充液|玻璃膜|試液|KCl（飽和），HgCl（s）|Hg（+）pHs-25型酸度計(jì)使用復(fù)合電極，玻璃電極為負(fù)極，銀-氯化銀電極為正極（-）玻璃電極|待測(cè)溶液|銀-氯化銀（+）

2、在實(shí)際工作中，采用兩次測(cè)量法，pHs=pHs+（Ex-Es）/0.059實(shí)驗(yàn)操作要求：校準(zhǔn)一用一種標(biāo)準(zhǔn)緩沖液按pH計(jì)的使用方法校準(zhǔn)pH計(jì)檢驗(yàn)一用校準(zhǔn)好了的pH計(jì)測(cè)量另一種與校準(zhǔn)時(shí)所用緩沖溶液的pH相差3個(gè)單位左右的標(biāo)準(zhǔn)緩沖液，測(cè)量值與表中所列值相差不應(yīng)大于0.1pH單位測(cè)定一用校準(zhǔn)好了的pH計(jì)測(cè)定待測(cè)溶液的pH2、電位滴定對(duì)于容量滴定中的酸堿都能滴定，且對(duì)于一些突躍范圍小，無(wú)合適指示劑，溶液渾濁，有色的酸堿，都能滴定。此外它還可測(cè)弱酸弱堿的解離常數(shù)，還可用來(lái)尋找合適指示劑或校正指示劑的終點(diǎn)顏色變化。磷酸為多元酸，其pKa可用電位滴定法測(cè)定當(dāng)磷酸的第一個(gè)H+被滴定一半時(shí)，此時(shí)的pH即為第一步的解

3、離常數(shù)。三、實(shí)驗(yàn)步驟（一）1、用鄰苯二甲酸氫鉀pH=4.00，測(cè)定草酸三氫鉀及混合磷酸鹽的pH值2、用混合磷酸鹽定位pH=6.88,測(cè)定硼砂及鄰苯二甲酸氫鉀的pH值（二）1、實(shí)驗(yàn)操作（1）、打開(kāi)電腦上的軟件，用磷酸混合溶液及鄰苯二甲酸氫鉀標(biāo)準(zhǔn)溶液校準(zhǔn)pH計(jì)，保存校準(zhǔn)數(shù)據(jù)，接著設(shè)置滴定條件，準(zhǔn)備滴定。（2）、用10.0ml移液管吸取磷酸樣品溶液10.0ml置于100ml燒杯中，加蒸餾水20ml，放入轉(zhuǎn)子，調(diào)節(jié)轉(zhuǎn)速，放入復(fù)合電極以及氫氧化鈉滴液管。點(diǎn)擊開(kāi)始，儀器開(kāi)始滴定，并自動(dòng)記錄實(shí)驗(yàn)數(shù)據(jù)。滴定結(jié)束后，停止滴定，保存數(shù)據(jù)及滴定曲線。2、數(shù)據(jù)處理，做出一階微商曲線，算出磷酸濃度以及第一第二解離常數(shù)。

4、四、實(shí)驗(yàn)數(shù)據(jù)溶液pH值測(cè)定結(jié)果表鄰苯二甲酸氫鉀定位（pH=4）混合磷酸鹽定位（pH=6.88）次數(shù)123次數(shù)123草酸三氫鉀1.621.631.60鄰苯二甲酸氫鉀4.074.064.05混合磷酸鹽6.856.866.86硼砂9.239.249.25磷酸的電位滴定數(shù)據(jù)記錄體積（mL）pH值一次導(dǎo)數(shù)二次導(dǎo)數(shù)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由數(shù)據(jù)所繪制的滴定曲線求得平均濃度為1/2(0.1029+0.1073)=0.1051mol/l由數(shù)據(jù)查得pKa1=2.3pKa2=6.9五、實(shí)驗(yàn)結(jié)論在pH定位為4的情況下，測(cè)得草酸三氫鉀的pH為1.62,混合磷酸鹽