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Practical chemistry for exams›CP 7 - Analysis of some inorganic and organic unknowns

CP 7 - Analysis of some inorganic and organic unknowns

An overview of CP 7 - Analysis of some inorganic and organic unknowns
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In Edexcel Core Practical 7: Identify unknown organic liquids and inorganic solids, a series of tests to identify unknown organic liquids (A, B, C) and inorganic solids (X, Y, Z) is carried out.

The tests will help in identifying the unknown substances through chemical reactions and observable results.

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In Edexcel core practical 7: Identify unknown organic liquids and inorganic solids, there are several important safety requirements to be aware of (beyond normal lab practice such as wearing goggles).

  • Unknown organic liquids must be treated as harmful and flammable.
  • Unknown inorganic solids must be regarded as harmful.
  • Potassium dichromate(VI) is corrosive, oxidising, and carcinogenic.
  • Potassium manganate(VII) is an oxidising agent.
  • Ethanol is flammable.
  • Silver nitrate solution is corrosive.
  • Chlorine water is toxic.
  • Dilute ammonia produces an irritating gas.
  • 0.1 mol* dm–3 barium chloride solution is *harmful.
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The image depicts a series of experimental steps for testing organic liquids as part of the Edexcel Core Practical. Each step includes instructions and illustrations of test tubes labeled X, Y, and Z with corresponding chemical reagents. Step 1: Add 10 drops of each liquid to separate test tubes. Add 1 cm³ of bromine water to each test tube and shake. Test tubes are vertically aligned with labels 'Bromine water' and 'Chemical samples' below. Step 2: Add 10 drops of each liquid to separate test tubes. Add 1 cm³ of acidic potassium dichromate to each tube and warm in a 60°C water bath for 5 minutes. Test tubes are shown above a water bath labeled 'Acidified potassium dichromate.' Step 3: Add 10 drops of each liquid to separate test tubes. Add 1 cm³ of Fehling’s solution to each tube, heat, and record observations. Test tubes are shown above a water bath labeled 'Fehling’s solution.' Step 4: Add 10 drops of each liquid to separate test tubes. Add 1 cm³ of ethanol and 1 cm³ of dilute sodium hydroxide. Warm in a water bath for 5 minutes, then add dilute nitric acid and 5 drops of silver nitrate solution. Test tubes are shown above a water bath with labels 'Ethanol,' 'Dilute sodium hydroxide,' 'Dilute nitric acid,' and 'Silver nitrate solution.' Step 5: Record your results in a table. The table has columns for 'Tube,' 'Bromine water,' 'Fehling’s solution,' and 'Acidified potassium dichromate.'
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The image is a six-step experimental method diagram titled 'EXPERIMENTAL METHOD EDEXCEL CORE PRACTICAL 7 - INORGANIC SOLIDS'. Step 1: Perform flame tests. A nichrome wire loop is cleaned by dipping in concentrated hydrochloric acid, then dipped into an unknown solid and placed in a blue Bunsen burner flame. Step 2: Prepare solutions for testing. Dissolve a spatula of each solid in 10 cm³ distilled water and split into three portions. Step 3: Silver nitrate test. Add 5 cm³ dilute nitric acid to the first portion, then 10 drops of silver nitrate solution, and dilute ammonia solution. Step 4: Barium chloride test. Add 5 cm³ dilute nitric acid to the second portion, followed by 10 drops of barium chloride solution. Step 5: Chlorine water test. Add 2 cm³ of chlorine water to the third portion. Step 6: Record results in a table. A table labeled 'Observations' with columns for 'Flame test', 'Reaction with dilute nitric acid followed by silver nitrate and dilute ammonia solution', 'Reaction with barium chloride solution', and 'Reaction with chlorine water'.
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Wearing the appropriate personal protective equipment is essential to avoid direct contact with harmful chemicals and to ensure safety throughout the experiment.

A simple illustration of a pair of goggles and gloves.
Do

Wear goggles and gloves when handling any chemicals, particularly concentrated acids, ammonia, and metal salts, as they can be corrosive or irritating to the skin and eyes.

A person wearing no goggles or gloves whilst handling chemicals.
Don't

Skip protective equipment just because ‘it’s only a few drops’.

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It is crucial to use clean and dry glassware when performing analytical tests.

Five test tubes arranged in a row, with varying heights and shapes.
Do

Ensure all glassware is clean and dry before use to avoid contamination and ensure accurate results.

A test tube with a white body and brownish stains or markings on its surface.
Don't

Reuse glassware that has not been properly cleaned and dried, as this could lead to inaccurate readings or unintended chemical reactions.

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Proper disposal of chemicals is essential to avoid environmental damage and ensure safe laboratory practices. Always follow disposal guidelines.

A diagram showing a chemically compatible container with screw-on cap labeled 'HAZARDOUS WASTE' placed inside a secondary container. There are labels indicating 'Labelling according to the local and national regulations'.
Do

Dispose of chemicals safely after testing by placing them in the designated waste containers. Always follow your teacher’s instructions for disposal.

A funnel pouring blue liquid into a drain.
Don't

Pour chemicals down the drain unless specifically directed to do so, as some chemicals may cause harmful reactions in the plumbing or be harmful to aquatic organisms.

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Results can be compared with positive test results for organic and inorganic ions to identify those present.

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