實驗三 沉澱滴定法 結報.docx - 實驗三...

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實驗三 沉澱滴定法 結報 化學 107 C34034067 鄭羽閎 A 1 1 數據處理: AgNO 3 溶液及 KSCN 溶液配置》 AgNO 3(aq) 0.8484 g / 250 mL → [AgNO 3 ] = 0.8484 / 169.88 / 0.25 = 0.01998 M KSCN (aq) 0.1945 g / 100 mL 理論得 [KSCN] = 0.1945 / 97.18/ 0.1 = 0.02001M 未知氯化物重量 0.1820 g / 250 mL 《用 AgNO 3 標定 KSCN 濃度》 #1 AgNO 3 體積 15.0 mL 耗去 KSCN 15.3 mL → #1 [KSCN] = 0.01998 × 15.0 ÷ 15.3 = 0.01959 M #2 AgNO 3 體積 15.0 mL 耗去 KSCN 15.5 mL →#2 [KSCN] = 0.01998 × 15.0 ÷ 15.5 = 0.01934 M [KSCN] 平均 = 0.01947 M 《分析未知物》 方法 Volhard method Mohr method Fajans method 滴定體積 AgNO 3 (ml) KSCN(ml) AgNO 3 (ml) AgNO 3 (ml) 未知氯化物 (25ml) 20 8 12.1 12 20 7.8 12.3 12.1 平均體積 20 7.9 12.2 12.05 (1) Volhard method [0.01998 × 20 0.01947 × 7.9] × 10 -3 = 2.458 × 10 -4 mole (2)Mohr method 12.2 × 0.01998 × 10 -3 = 2.436 × 10 -4 mole (3)Fajans method 12.05 × 0.01998 × 10 -3 = 2.408 × 10 -4 mole 平均 = 2.434× 10 -4 mole 未知物分子量 = 0.1820× ( 25 ÷ 250 ) ÷ ( 2.434 × 10 -4 ) = 74.774 g / mol 2 問題與討論: 1. 說明 Volhard 法、 Mohr 法、 Fajans 法的分析原理,並比較其優、缺點。 Volhard 法》 以過量的 AgNO 3 aq 加入含有鹵素陰離子 (X - ) 的分析物中,使其產生 AgX (s) 沉澱,再用 KSCN 的標準液來滴定過量(即剩餘的)的 Ag + ,如下面反應式: Ag + + SCN - → AgSCN (s) 然後再加入鐵明礬 ( Fe 3+ ) 指示劑,而過量的 SCN - ,會與 Fe 3+ 反應形成
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Fe(SCN) 2+ 的紅色錯離子 ( 赤血鹽 ) ,此時即達到滴定終點。 優點: (1) 由於 Volhard 法須在強酸環境下進行,所以溶液中的部分弱酸離子 形成,就不會對實驗生成干擾。 ( 在中性溶液中,部分酸性離子會
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