Задача по идентификации неизвестных веществ

Определение таинственных порошков по физическим и химическим свойствам

Qualitative Analysis Intermediate (High School) 75 мин ~$10,00

Цель

Применить несколько качественных тестов для идентификации неизвестных белых порошков, развивая навыки системного аналитического мышления.

Предпосылки

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.

Предупреждения по безопасности

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

Требуемые СИЗ

goggles gloves lab_coat

Материалы

  • 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

Оборудование

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

Процедура

1

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

10 мин
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 мин
3

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

5 мин
4

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

10 мин
5

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

5 мин
6

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

15 мин 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 мин Use tongs to handle hot dish
8

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

10 мин

Ожидаемые результаты

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.

Уборка

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

Детали

Категория
Qualitative Analysis
Сложность
Intermediate (High School)
Продолжительность
75 мин
Прим. стоимость
$10,00
Шаги
8
Материалы
6

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Frequently Asked Questions

What is the objective of Задача по идентификации неизвестных веществ?
Применить несколько качественных тестов для идентификации неизвестных белых порошков, развивая навыки системного аналитического мышления.
How difficult is Задача по идентификации неизвестных веществ?
This experiment is rated as Intermediate (High School). It takes approximately 75 minutes to complete.
What safety precautions are needed for Задача по идентификации неизвестных веществ?
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 Задача по идентификации неизвестных веществ?
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 Задача по идентификации неизвестных веществ?
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.