未知物质鉴定挑战

用物理和化学性质鉴定神秘粉末

Qualitative Analysis Intermediate (High School) 75 分钟 ~$10.00

目标

对未知白色粉末应用多种定性测试，培养系统分析思维能力。

背景

This integrative experiment challenges students to identify unknown white powders from a set of possibilities (NaCl, NaHCO₃, CaCO₃, cornstarch, sugar, baking powder) using a battery of physical and chemical tests. Students must design their own testing sequence, demonstrating understanding of solubility, acid reactivity, flame tests, and indicator tests.

安全警告

  • Do not taste any unknown samples
  • Wear goggles when heating or adding acid to unknowns
  • Some unknowns may react vigorously with acid

所需PPE

goggles gloves lab_coat

材料

  • Unknown powders (3–5 samples) (2 g each)
    Labeled A, B, C, etc.
  • Dilute HCl (1M) (10 mL)
    For acid reactivity test
  • Distilled water (100 mL)
    For solubility test
  • Iodine solution (5 mL)
    Starch test
  • Universal indicator (5 mL)
    pH test
  • Cobalt chloride paper (5 strips)
    Water of crystallization test

设备

Test tubes (10) Bunsen burner Nichrome wire loop Spatula Magnifying glass Evaporating dish

步骤

1

Observe each unknown's physical appearance under magnifying glass: crystal shape, texture, color. Record observations.

10 分钟
2

Solubility test: Add 0.5 g of each unknown to 5 mL distilled water. Stir and observe if it dissolves, partially dissolves, or is insoluble.

10 分钟
3

pH test: Add 2 drops of universal indicator to the dissolved/suspended samples. Record the pH.

5 分钟
4

Acid reactivity: Add 5 drops of dilute HCl to a small amount of each dry unknown. Record any effervescence (CO₂ evolution).

10 分钟
5

Iodine test: Add 2 drops of iodine solution to each unknown dissolved in water. Record color change.

5 分钟
6

Flame test: Using a clean nichrome wire, test each unknown in the Bunsen burner flame.

15 分钟 Keep face away from flame
7

Heat test: Gently heat a small amount of each unknown in an evaporating dish. Observe melting, charring, or gas evolution.

10 分钟 Use tongs to handle hot dish
8

Compile all results and cross-reference to identify each unknown. Write your reasoning.

10 分钟

预期结果

NaCl: soluble, neutral pH, no acid reaction, yellow flame. NaHCO₃: soluble, basic pH, effervesces with acid. CaCO₃: insoluble, effervesces with acid, orange-red flame. Cornstarch: insoluble, positive iodine test. Sugar: soluble, chars on heating.

清理

Dispose of acid-reacted solutions in waste container. Clean all test tubes and glassware. Return unused unknown samples.

详情

类别
Qualitative Analysis
难度
Intermediate (High School)
时长
75 分钟
预估费用
$10.00
步骤数
8
材料
6

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Frequently Asked Questions

What is the objective of 未知物质鉴定挑战?
对未知白色粉末应用多种定性测试，培养系统分析思维能力。
How difficult is 未知物质鉴定挑战?
This experiment is rated as Intermediate (High School). It takes approximately 75 minutes to complete.
What safety precautions are needed for 未知物质鉴定挑战?
Key safety precautions include: Do not taste any unknown samples; Wear goggles when heating or adding acid to unknowns; Some unknowns may react vigorously with acid.
What materials are needed for 未知物质鉴定挑战?
The main materials required are: Unknown powders (3–5 samples), Dilute HCl (1M), Distilled water, Iodine solution, Universal indicator.
What results should I expect from 未知物质鉴定挑战?
NaCl: soluble, neutral pH, no acid reaction, yellow flame. NaHCO₃: soluble, basic pH, effervesces with acid. CaCO₃: insoluble, effervesces with acid, orange-red flame. Cornstarch: insoluble, positive iodine test. Sugar: soluble, chars on heating.