ANDREW LAMBERT PHOTOGRAPHY / SCIENCE PHOTO LIBRARY ANDREW LAMBERT PHOTOGRAPHY / SCIENCE PHOTO LIBRARY
Benedict's test for sugars. The test tubes contain sugar solutions of different strengths. From left to right: pure water, 0.1% sugar, 0.3%, 1% and 3%. A positive test results in an orange precipitate, which is seen in varying densities in the tubes. Benedict's reagent is a solution of copper (II) sulphate (CuSO4), tartaric acid and sodium hydroxide. In the presence of sugars, the copper sulphate is reduced to insoluble orange copper (I) oxide. Not all sugars give the positive result: sucrose, for instance, does not.
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