양이온 정성분석. 양이온 계통분석

양이온 정성분석. 양이온 계통분석

Qualitative analysis of cations

 

 

 

시료 용액에,

6 M HCl을 가한 다음, 침전물을 거른다.

---> 양이온 제1족 침전 분리

---> AgCl, PbCl2, Hg2Cl2

 

Ag^+(aq) + Cl^-(aq) → AgCl(s)

Pb^2+(aq) + 2Cl^-(aq) → PbCl2(s)

Hg2^2+(aq) + 2Cl^-(aq) → Hg2Cl2(s)

 

> 만약 시료 용액에 Ag^+, Pb^2+, Hg2^2+ 이온이 없으면,

이 단계에서 침전이 발생하지 않는다.

> 즉, 이 단계에서 침전이 발생한다는 것은

시료 용액에 Ag^+, Pb^2+, Hg2^2+ 이온이

전부 또는 일부가 존재한다는 것이다.

 

 

 

침전물을 거르고 남은 용액에,

H2S + 0.2 M HCl을 가한 다음, 침전물을 거른다.

---> 양이온 제2족 침전 분리

---> CuS, CdS, Bi2S3, PbS, HgS, As2S3, Sb2S3, SnS2

 

 

 

침전물을 거르고 남은 용액에,

pH = 8인 (NH4)2S를 가한 다음, 침전물을 거른다.

---> 양이온 제3족 침전 분리

---> Al(OH)3, Fe(OH)3, Cr(OH)3, ZnS, NiS, MnS, CoS

 

 

 

침전물을 거르고 남은 용액에,

(NH4)2HPO4 + NH3를 가한 다음, 침전물을 거른다.

---> 양이온 제4족 침전 분리

---> Ca3(PO4)2, Sr3(PO4)2, Ba3(PO4)2, MgNH4PO4

 

 

 

침전물을 거르고 남은 용액

---> 양이온 제5족

---> 알칼리 금속 이온과 NH4^+

 

 

 

 

 

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Group 1. Insoluble chlorides

> Of the common metal ions, only Ag^+, Hg2^2+, and Pb^2+ form insoluble chlorides. When HCl is added to a mixture of cations, therefore, only AgCl, Hg2Cl2, and PbCl2 precipitate, leaving the other cations in solution.

 

 

 

Group 2. Acid-insoluble sulfides

> After any insoluble chlorides have been removed, the remaining solution, now acidic from HCl treatment, is treated with H2S. Since H2S is a weak acid compared to HCl, its role here is to act as a source for small amounts of sulfide. Only the most insoluble metal sulfides - CuS, Bi2S3, CdS, PbS, HgS, As2S3, Sb2S3, and SnS2 – precipitate.

 

 

 

Group 3. Base-insoluble sulfides and hydroxides

> After the solution is filtered to remove any acid-insoluble sulfides, it is made slightly basic, and (NH4)2S is added. In basic solutions the concentration of S^2- is higher than in acidic solutions. Under these conditions, the ion products for many of the more soluble sulfides exceed their Ksp values and thus precipitation occurs. The metal ions precipitated at this stage are Al^3+, Cr^3+, Fe^3+, Zn^2+, Ni^2+, Co^2+, and Mn^2+.

 

 

 

Group 4. Insoluble phosphates

> At this point, the solution contains only metal ions from groups 1A and 2A of the periodic table. Adding (NH4)2HPO4 to a basic solution precipitates the group 2A elements Mg^2+, Ca^2+, Sr^2+, and Ba^2+ because these metals form insoluble phosphates.

 

 

 

Group 5. The alkali metal ions and NH4^+

> The ions that remain after removing the insoluble phosphates are tested for individually. A flame test can be used to determine the presence of K^+, for example, because the flame turns a characteristic violet color if K^+ is present.

 

 

 

 

[ 자료 https://web.williams.edu/wp-etc/chemistry/epeacock/EPL_CHEM_153/153-LABMAN_PDF_05/2-3-qualanalysis.pdf ] Qualitative Analysis of Metal Ions in Solution

 

[ 관련 글 https://byjus.com/chemistry/systematic-analysis-of-cations/ ] systematic analysis of cations

 

 

 

[키워드] 양이온 정성분석 기준, 분리분석 기준, 양이온 분석 기준, 양이온 분리 기준, 양이온 정성분석 사전