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Water

Water. Aqueous Systems and Solutions. Water. Simple, triatomic molecule Polar covalent bonds Polar molecule Hydrogen bond(F-H, O-H, N-H) High surface tension Low vapor pressure High specific heat High heat of vaporization High boiling point. Surface Properties. High surface tension

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Water

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  1. Water Aqueous Systems and Solutions

  2. Water • Simple, triatomic molecule • Polar covalent bonds • Polar molecule • Hydrogen bond(F-H, O-H, N-H) • High surface tension • Low vapor pressure • High specific heat • High heat of vaporization • High boiling point

  3. Surface Properties • High surface tension • Cohesive forces caused by hydrogen bonding • The inward force or pull which tends to minimize the surface area of a liquid is surface tension. • Allow some objects to float(needles,bugs) • May be decreased by use of a wetting agent such as soap or detergent(surfactant)

  4. Aqueous Solutions • Water is not found pure because it is one of the best solvents known. • In a solution the dissolving medium is the solvent and the dissolved particles are the solute. • True solutions have several properties: • Homogeneous • Do not settle • Particles are ionic or molecular • They cannot be filtered.

  5. Solvation • In some ionic compounds the attractive forces within the crystals are stronger than the attractive forces exerted by the solvent. That kind of solid does not dissolve well. (insoluble) • The general rule is like dissolves like but IMF play a role also.

  6. Which of the following will dissolve in water? • Hydrochloric acid • Sodium iodide • Ammonia • Magnesium sulfate • Methane • Gasoline • Grease

  7. Water of Hydration • The water in a crystal is called the water of hydration or water of crystallization. • Copper (II) sulfate pentahydrate is an example. • Water can be driven from the crystals by gentle heating. • If the hydrate has a vapor pressure higher than atmospheric pressure then the crystal will effloresce or lose its water of hydration. • If the compound has a very low vapor pressure then it will remove moisture from the air. It is deliquescent.

  8. Water of Hydration • If they only draw small quantities of water from the air, they are hygroscopic. • Hygroscopic substances are used to dry materials and are called dessicants.

  9. Suspensions and Colloids • Suspensions are mixtures from which some particles will settle upon standing. • Its particles are larger(>100 nm) than those of a true solution(<1 nm) • Its particles can be trapped by filtration. • Colloids are mixtures containing particles (1 nm-100 nm) that are intermediate in size. • They are usually milky or cloudy. • They cannot be filtered nor will they settle. • They exhibit the Tyndall Effect, which is the scattering of visible light in all directions.

  10. Suspensions and Colloids • The chaotic movement of colloidal particles is called Brownian motion. • For a summary of solutions, colloids, and suspensions see page 363. • Emulsions are colloidal dispersions of liquids in liquids. Soaps and detergents are emulsifying agents.

  11. Electrolytes and Nonelectrolytes • Electrolytes are substances which conduct electric current. • These substances may be aqueous or molten. • Electrolytes may be strong or weak. A strong electrolyte has many ions in solution.

  12. Factors Affecting Rate of Dissolution • Surface area of solute • Agitation • Heating

  13. Solubility • Defined as the number of grams of solute per 100g of solvent at a given temperature • Saturated solution – a solution that contains as much solute as possible at that temperature. • Unsaturated solution – a solution that contains less solute than the maximum at that temperature. • Supersaturated solution – a solution that contains more than the maximum at that temperature.

  14. Heat Capacity of Water • 1 calorie per gram per oC. • Quantity of energy needed to raise 1.00 g of a substance 1 oC • Cp • q = mCpDt

  15. Vaporization of Water • Heat of vaporization of water = 540 cal/g. • Quantity of energy needed to vaporize 1.00 gram of substance at its normal boiling point. • Compare water(540cal/g, gfm = 18, 100oC), ammonia(327 cal/g, gfm = 17, -33oC), and methane(122 cal/g, gfm = 16, bp)

  16. Ice • Water has its greatest density at 4oC. • Phase diagrams show transitions of substances very concisely.

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