金属イオンのホウ砂ビーズ試験

ホウ砂融合で形成される着色ガラスビーズで遷移金属を同定する

Qualitative Analysis Intermediate (High School) 45 分 ~$8.00

目的

遷移金属イオンがホウ砂（四ホウ酸ナトリウム）のガラスビーズに融合したときに生じる特徴的な色を利用して遷移金属イオンを同定する。

背景

The borax bead test is an elegant method for identifying transition metal ions. When borax (Na₂B₄O₇·10H₂O) is heated, it loses water and forms a clear glassy bead of sodium metaborate. When a metal salt is dissolved into this bead, the metal ions become trapped in the glass matrix, producing characteristic colors. The color often differs between the oxidizing flame (outer cone) and reducing flame (inner cone), providing additional diagnostic information.

安全上の警告

  • Molten borax beads are extremely hot
  • Chromium compounds are irritants — avoid dust inhalation
  • Do not touch hot beads — let cool on a watch glass
  • Cobalt compounds are toxic if ingested

必要なPPE

goggles gloves lab_coat

材料

  • Borax (Na₂B₄O₇·10H₂O) (5 g)
    Powdered
  • Metal salt samples (0.5 g each)
    CuSO₄, CoCl₂, NiCl₂, FeCl₃, MnCl₂, Cr₂O₃
  • Unknown metal salt (0.5 g)

器具

Platinum wire loop (or nichrome alternative) Bunsen burner Forceps Watch glasses (7)

手順

1

Make a small loop at the end of the platinum wire. Heat the loop in the hottest part of the flame until red-hot.

2 分 Wire is very hot
2

Dip the hot wire into powdered borax. Return to the flame and heat until a clear, transparent glass bead forms. Repeat dipping and heating if needed to build up the bead.

5 分
3

Touch the hot bead to a tiny amount of CuSO₄ powder. Return to the oxidizing flame (outer cone). Observe the color (should be blue-green).

5 分
4

Now heat the same bead in the reducing flame (inner cone, blue). The color may change to red (metallic copper).

3 分
5

Make fresh beads and repeat for each metal salt. Record colors in both oxidizing and reducing flames, both hot and cold.

20 分
6

Test the unknown salt and match the bead colors to your reference chart.

10 分

予想される結果

Cu: blue-green (oxidizing), red (reducing). Co: deep blue (both). Ni: gray-brown (oxidizing), gray (reducing). Fe: yellow-brown (oxidizing), green (reducing). Mn: violet (oxidizing), colorless (reducing). Cr: green (both, darker in reducing).

後片付け

Allow all beads to cool completely. Dispose of transition metal waste appropriately. Clean the platinum wire by fusing with fresh borax until clear.

詳細

カテゴリ
Qualitative Analysis
難易度
Intermediate (High School)
所要時間
45 分
推定費用
$8.00
ステップ数
6
材料
3

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Frequently Asked Questions

What is the objective of 金属イオンのホウ砂ビーズ試験?
遷移金属イオンがホウ砂（四ホウ酸ナトリウム）のガラスビーズに融合したときに生じる特徴的な色を利用して遷移金属イオンを同定する。
How difficult is 金属イオンのホウ砂ビーズ試験?
This experiment is rated as Intermediate (High School). It takes approximately 45 minutes to complete.
What safety precautions are needed for 金属イオンのホウ砂ビーズ試験?
Key safety precautions include: Molten borax beads are extremely hot; Chromium compounds are irritants — avoid dust inhalation; Do not touch hot beads — let cool on a watch glass.
What materials are needed for 金属イオンのホウ砂ビーズ試験?
The main materials required are: Borax (Na₂B₄O₇·10H₂O), Metal salt samples, Unknown metal salt.
What results should I expect from 金属イオンのホウ砂ビーズ試験?
Cu: blue-green (oxidizing), red (reducing). Co: deep blue (both). Ni: gray-brown (oxidizing), gray (reducing). Fe: yellow-brown (oxidizing), green (reducing). Mn: violet (oxidizing), colorless (reducing). Cr: green (both, darker in reducing).