Concentrated sulphuric acid H₂SO₄ is a dehyrating agent. It will extract water from any compound or any mixture. We say that it has great affinity for water molecules. The test tube on the right shows blue hydrated copper sulphate crystals. Each formula unit is CuSO₄.5H₂O. When water is extracted from the latter, it turns white to becomes white anhydrous copper sulphate, as shown on the upper portion of the the test tube on the left.

CuSO₄.5H₂O → CuSO₄ + 5H₂O

Note that the 5H₂O in the hydrated blue crystal is known as the water of crystallisation.

The simplest of sugar is called glucose C₆H₁₂O₆ When water is extracted from glucose, black carbon (C) is left behind as shown by the right test tube.  

C₆H₁₂O₆ → 6C + 6H₂O
Black carbon is extracted by conc H₂SO₄