Crystals of copper sulfate appears blue as it contains 5 molecules of water. Its chemical formula is CuSO4.5H2O Sodium carbonate is also known as washing soda, it contains 10 molecules of water. Its chemical formula is Na2CO3⋅10H2O Gypsum is also known as calcium sulfate. It contains 2 molecules of water. Its chemical formula is CaSO4⋅2H2O