Glucose is called a reducing sugar. This is because the test for glucose involves chemicaly reducing an alkaline solution of copper sulphate to copper (I) oxide.
The test for glucose is called the Benedict's test. Simply add a few drops of Benedict's solution, which contains alkaline copper sulphate, to some glucose.
Add enough to turn the mixture blue.
Prepare a water bath by half filling a beaker with water and heating it on a tripod and gauze.
Heat the mixture in the boiling water bath.
The clear blue solution will gradually change colour, forming a cloudy orange or brick red precipitate of copper (I) oxide.
All 'single' sugars such as fructose are reducing sugars, as well as some 'double' sugars such as the milk sugar, lactose.
However ordinary table sugar (sucrose) is not. If sucrose is boiled with Benedict's solution it remains a clear blue colour.
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