本方法適用于工業(yè)級、熒光粉級碳酸鋰中質(zhì)量分?jǐn)?shù)為0.0030%～0.20%的氯化物的測定。                                                                

2   原理                                                                

試料用硝酸分解，在微酸性溶液或乙醇溶液(3＋1)中，以二苯偶氮羰酰肼為指示劑，用硝酸汞標(biāo)準(zhǔn)滴定溶液滴定至紫紅色確定終點(diǎn)。以消耗硝酸汞標(biāo)準(zhǔn)滴定溶液的量計(jì)算氯化物的量。                                                                                                                                  

3   試劑                                                                                                                                 

3.1乙醇，3＋1。                                                                                                                                  

3.2硝酸，ρ1.42g/mL，優(yōu)級純。           &nbs

3.3硝酸，1+1，優(yōu)級純。                                                                                                                                  

3.4硝酸，3+47，優(yōu)級純。                                                                                                                                 

3.5氫氧化鈉溶液，200g/L。                                                                                                                                 

3.6氫氧化鈉溶液，40g/L。                                                                                                                                 &n

3.7氯化鈉標(biāo)準(zhǔn)貯存溶液，0.05moL/L：

稱取2.9220g預(yù)先在450～500℃灼燒1.5h并在干燥器中冷卻至室溫的氯化鈉(基準(zhǔn)試劑)，置于250mL燒杯中，加水溶解后，移入1000mL容量瓶中，以及稀釋至刻度，混勻。

3.8氯化鈉標(biāo)準(zhǔn)溶液，0.005moL/L：

移取25.00mL0.05moL/L氯化鈉標(biāo)準(zhǔn)貯存溶液，置于250mL容量瓶中，以水稀釋至刻度，混勻。                                                                 

3.9硝酸汞標(biāo)準(zhǔn)貯存溶液，0.05moL/L：

稱取8.57g硝酸汞[Hg(NO₃)₂·H₂O，優(yōu)級純]，置于250mL燒杯中。加入7mL硝酸(1+1)，用少量水溶解，必要時(shí)過濾，移入1000mL容量瓶中，以水稀釋至刻度，混勻。                                                                

注：或稱取5.43g氧化汞(優(yōu)級純)，置于250mL燒杯中，加入10mL硝酸(1+1)和少量水溶解，必要時(shí)過濾，移入1000mL容量瓶中，以水稀釋至刻度，混勻。                                                                                                                                 

3.10硝酸汞標(biāo)準(zhǔn)滴定溶液，0.005moL/L。

3.10.1配制：移取50.00mL0.05moL/L硝酸汞標(biāo)準(zhǔn)貯存溶液，置于500mL容量瓶中，補(bǔ)加5mL硝酸(1+1)，以水稀釋至于刻度，混勻。                                                                                                                                  

3.10.2標(biāo)定：移取三份5.00mL0.005moL/L氯化鈉標(biāo)準(zhǔn)溶液，分別置于250mL三角瓶中，加入40mL水和2～3滴1g/L溴酚藍(lán)指示劑，滴加硝酸(3+47)至溶液由藍(lán)色變?yōu)辄S色，再過量2～5滴，加入1mL 5g/L二苯偶氮羰酰肼指示劑，以硝酸汞標(biāo)準(zhǔn)滴定溶液，0.005moL/L滴定至溶液由黃色變?yōu)樽霞t色即為終點(diǎn)。平行標(biāo)定所消耗0.005moL/L硝酸汞標(biāo)準(zhǔn)滴定溶液體積的極差值不應(yīng)超過0.06mL，取其平均值。                                                                                                                               &n

注：如試料在乙醇介質(zhì)中滴定，則標(biāo)定也應(yīng)在相同介質(zhì)中進(jìn)行。                                                                                                                                  

隨同標(biāo)定做空白試驗(yàn)。                                                                                                                                  

按式(1)計(jì)算硝酸汞標(biāo)準(zhǔn)滴定溶液的實(shí)際濃度：

             （1）

式中：c—硝酸汞標(biāo)準(zhǔn)滴定溶液的實(shí)際濃度，moL/L；

c₁—氯化鈉標(biāo)準(zhǔn)溶液的濃度，moL/L；

V₁—氯化鈉標(biāo)準(zhǔn)溶液的體積，mL；

V—滴定氯化鈉標(biāo)準(zhǔn)溶液消耗硝酸汞標(biāo)準(zhǔn)滴定溶液的體積，mL；                                                                                                                                 

V

3.11溴酚藍(lán)指示劑，1g/L：用乙醇配制。

3.12二苯偶氮羰酰肼指示劑，5g/L：用乙醇配制。

4   儀器設(shè)備

10mL微量滴定管，精確至0.01mL。

5   操作步驟

5.1稱樣                                                                                                                                  

碳酸鋰預(yù)先在250～260℃烘2h，置于干燥器中冷卻至室溫。                                                                                                                                  

稱取3.000g試樣，精確至0.001g。                                                                                                                                 

獨(dú)立地進(jìn)行兩次測定，取其平均值。                                                                         

5.2空白試驗(yàn)                                                                                                                                 

隨同試料做空白試驗(yàn)。但加入與分解試料等量的酸，應(yīng)在低溫下蒸發(fā)至近干。                                                                                                                                  

5.3測定                                                                                                                                 

5.3.1將試料置于250mL三角瓶中，用少量水潤濕，加入6mL硝酸溶解。加水至約40mL(如試樣中氯質(zhì)量分?jǐn)?shù)小于0.008%時(shí)，加入30mL乙醇和4mL水)，加入2～3滴1g/L溴酚藍(lán)指示劑，用200g/L或40g/L氫氧化鈉溶液和調(diào)至藍(lán)色，再滴加硝酸(3+47)至恰呈黃色，并過量2～5滴。

5.3.2向試液(5.3.1)中加入1mL 5g/L二苯偶氮羰酰肼指示劑，用0.005moL/L硝酸汞標(biāo)準(zhǔn)滴定溶液滴定至試液由黃色變?yōu)樽霞t色即為終點(diǎn)。                                                                                                                                  

6   結(jié)果計(jì)算                &n

按下式(2)計(jì)算氯化物(以C1計(jì))的含量，以質(zhì)量分?jǐn)?shù)表示：

           （2）                                                                                            

式中： c—硝酸汞標(biāo)準(zhǔn)滴定溶液的實(shí)際濃度，moL/L；

V—滴定試液消耗硝酸汞標(biāo)準(zhǔn)滴定溶液的體積，mL；                                                                                                                                  

V₀—滴定空白溶液消耗硝酸汞標(biāo)準(zhǔn)滴定溶液的體積，mL；

m—試料的質(zhì)量，g；

0.03545—與1.00mL硝酸汞標(biāo)準(zhǔn)滴定溶液相當(dāng)?shù)穆然�物的質(zhì)量，g。

7   允許差

兩個(gè)測定值之間的的差值應(yīng)不大于下表所列允許差。

%

8   參考文獻(xiàn)

[1] 國家標(biāo)準(zhǔn)GB/T 11064.10-89