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PROPERTIES ASSOCIATED WITH WATER

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Presentation on theme: "PROPERTIES ASSOCIATED WITH WATER"— Presentation transcript:

1 PROPERTIES ASSOCIATED WITH WATER
HYDRATES: Solids that contain water molecules as part of their crystalline structure. The water in the hydrate is known as the water of hydration or the water of crystallization. HYGROSCOPIC: A substance is hygroscopic if it readily absorbs water from the atmosphere and forms a hydrate. DELIQUESCENT: A substance is deliquescent if it absorbs water from the air until it forms a solution. DESICCANTS: Compounds that absorb water and are used as drying agents. EFFLORESCENCE: The process by which crystalline materials spontaneously lose water when exposed to air.

2 Example: BaCl2•2H20 is called barium chloride dihydrate.
HYDRATES Hydrates formulas: are expressed by writing the anhydrous formula (without water) for the compound and then adding a dot followed by the number of water molecules present. Example: BaCl2•2H2O this formula tells that each formula unit contains one barium ion, two chloride ions and two water molecules. Naming Hydrates: first name the compound exclusive of the water, then add the term hydrate, with proper prefix, representing the number of water molecules in the formula. Example: BaCl2•2H20 is called barium chloride dihydrate.

3 BaCl2•2H2O(s)  BaCl2(s) + 2H2O(g)
HYDRATES Water molecules in hydrates are bonded by electrostatic forces between polar water molecule and the positive or negative ions of the compound. These forces are not as strong a covalent or ionic chemical bonds. As a result water of crystallization can be removed by moderate heating of the compound ºC BaCl2•2H2O(s)  BaCl2(s) + 2H2O(g) When a solution of copper (II) sulfate (CuSO4) is allowed to evaporate, beautiful blue crystals containing 5 moles water per 1 mole CuSO4 are formed. This formula for this hydrate is CuSO4•5H20 called copper (II) sulfate pentahydrate. When CuSO4•5H2O is heated, water is lost,a pale green-white powder , anhydrous CuSO4 is formed ºC CuSO4•5H2O(s)  CuSO4(s) + 5H2O(g) When water is added to anhydrous copper (II) sulfate, the reaction is reversed and the compound turns blue again. The formation of the hydrate is noticeably exothermic.

4 PRACTICE PROBLEMS See empirical Formula
Magnesium carbonate, MgCO3, forms a hydrate containing 39.1 % water of hydration. Calculate & name the formula of this hydrate. 2. A 25.0 g sample of a hydrate of FePO4 was heated until all the water was driven off. The mass of anhydrous sample is 16.9 g. What is the formula & name of the hydrate? MgCO3 . 3 H2O Magnesium carbonate trihydrate FePO4 . 4 H2O Iron(III) phosphate tetrahydrate


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