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Module 1: Practical chemistry for exams›PAG 12.2 - Investigating the copper content of brass screws

PAG 12.2 - Investigating the copper content of brass screws

An overview of PAG 12.2 - Investigating the copper content of brass screws
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In OCR Chemistry Required Practical 12 (PAG 12.2), the copper composition of a brass screw/bolt is identified based around a redox titration using sodium thiosulfate solution and its reaction with iodine.

For this reaction to work several steps are carried out, the associated equations can be found below.

  • Dissolving the brass item will form copper ions:

  • Reaction of copper and iodide ions occur when potassium iodide is added and elemental iodine is formed:

  • The iodine is titrated with sodium thiosulfate with a starch indicator:

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In OCR PAG 12.2: Investigating the copper content of brass screws, there are several important safety requirements to be aware of (beyond normal lab practice such as wearing goggles).

  • Fumes will be produced when dissolving the screws – carry this out in a fume cupboard.
  • Concentrated nitric acid causes severe skin burns – wear chemical-resistant gloves.
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Experimental method for OCR Chemistry Required Practical 12 (PAG 12.2)

The image depicts a nine-step experimental method for preparing and purifying a chemical compound. Step 1: Accurate weighing of a solid using a balance and a weighing boat. Step 2: Dissolving the solid in water within a beaker. Step 3: Transferring the solution to a volumetric flask using a funnel, then diluting to the mark with water. Step 4: Preparing a reaction mixture in a conical flask with a stopper, including a labeled addition of a liquid reactant via a pipette. Step 5: Repeated weighing of a weighing bottle to ensure accurate mass. Step 6: Addition of the solution from a burette to the conical flask, with a visible meniscus alignment. Step 7: Tabulation of experimental results, including initial and final readings. Step 8: Final titration setup with a labeled burette reading. Step 9: Observation of color change upon completion of the titration process, indicating the endpoint. Each step includes detailed illustrations and annotations such as '250 ml conical flask,' 'funnel,' 'pipette,' and 'meniscus.'
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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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Calculate moles of thiosulfate using:

Use and to work back to the moles and mass of overall,

Calculate the percentage of copper in the brass using:

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