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A-Level Biology OCR A

Solution Benedict's Method Qualitative Sugar Tested Reaction Brick

Benedict's test uses Benedict's solution (alkaline copper(II) sulfate) to detect reducing sugars. The mixture is heated (80+°C), and a positive result yields a brick-red precipitate (Cu+), while a negative result remains blue.

La prueba de Benedict utiliza solución de Benedict (sulfato de cobre(II) alcalino) para detectar azúcares reductores. Se calienta la mezcla (80+°C), y un resultado positivo da un precipitado rojo ladrillo (Cu+), mientras que un resultado negativo mantiene el color azul.

Front What are the chemical used in the Benedict's test? Outline the method & the appearance of a negative/positive result.
Back Benedict's test

Substances used
  • Qualitative Benedict's solution (alkaline solution of copper(II)sulfate)
  • Solution you are testing (reducing/non-reducing sugar)


Method
  • Sugar being tested must be in solution so that reducing sugar molecules can expose their aldehyde group in linear form
  • Add qualitative benedicts solution in equal volume to sample being tested - reactants will be in excess so reaction will be complete
  • Heat mixture to 80+ deg C - catalysing reaction

Results
  • Brick red precipitate - Cu2+ ions reduced to Cu+ - brick red color - positive result
  • No color change - solution stays blue - negative result

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