Download - Water
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 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)
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.
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.
Which of the following will dissolve in water?
Hydrochloric acid Sodium iodide Ammonia Magnesium sulfate Methane Gasoline Grease
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.
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.
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.
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.
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.
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.
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 = mCpt
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)