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Chapter 17. Water. Section 17.1. Water is a very polar molecule. The oxygen is electronegative. The hydrogens are electropositive. Water molecules are attracted to each other by Hydrogen bonds. The results of these bonds are that water has a: High surface tension

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Chapter 17

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Chapter 17

Chapter 17


Section 17 1

Section 17.1

  • Water is a very polar molecule.

    • The oxygen is electronegative.

    • The hydrogens are electropositive.

  • Water molecules are attracted to each other by Hydrogen bonds. The results of these bonds are that water has a:

    • High surface tension

    • High specific heat capacity

    • High heat of vaporization

    • High boiling point.

Why does water form a ball on a sheet of paper

Why does water form a ball on a sheet of paper?

  • Hydrogen bonds!

  • Water has a high surface tension:

    • The inward force or pull that tends to minimize the surface area of a liquid.

  • You can decrease the surface tension by adding a surfactant:

    • A wetting agent such as soap or detergent.

      • These detergents interfere with the hydrogen bonding.

Why does water have a low vapor pressure

Why does water have a low vapor pressure?

  • Hydrogen Bonds!

  • The water molecules hold onto each other so that water doesn’t escape into the gaseous phase.

Why does water have a high specific heat capacity

Why does water have a high specific heat capacity?

  • Hydrogen Bonds!!

  • It takes 4.18 J (1 cal) to raise 1 g of water 1˚C.

    • Do metals have a higher or lower heat capacity?

      • Lower

  • Why does this factor help to moderate?

    • Our temperatures – summer – relatively mild and winter relatively mild.

Section 17 2

Section 17.2

  • Heat of Vaporization:

    • Amount of energy needed to convert 1 g of a substance from a liquid to a gas at the boiling point.

  • Condensation:

    • Going from a gas to a liquid – the amount of energy removed in order to convert 1 g of a substance from a gas to a liquid at the boiling point.

  • Molecular compounds that have low molecular mass are usually gas or liquids at room temperature and have low boiling points. (NH3 boils at -33˚C)

    • Water, a molecular compound with low molar mass, is high (boils at 100˚C). Why?

What happens when a liquid cools

What happens when a liquid cools?

  • The molecules move closer and closer, the density increases, and eventually the liquid turns to a solid and sinks.

  • Water behaves like this for only so long. At 4˚C, water is the densest it will be. Below this temperature water is actually decreasing in density.

  • When water reaches 0˚C, water turns to a solid and floats.

    • Why?

      • When ice forms, the hydrogen bonds make the molecules form a honeycomb type of structure. This makes it less dense.

  • What would happen if ice were to become more dense than liquid water in real life?

Section 17 3

Section 17.3

  • Aqueous solutions:

    • Water samples containing diessolved substances.

    • Solvent:

      • Dissolving medium

    • Solute:

      • Dissolved particles

    • Substances that dissolve readily in water:

      • Ionic compounds

      • Polar covalent molecules

      • Nonpolar covalent molecules don’t (oil, grease)

    • Solvation:

      • The process that occurs when a solute dissolves.

Like dissolves like

“Like Dissolves Like”

+ =

- =

H2O =

This occurs until all of the solid chunk have been “carried off”,

dissolved, by the dissolving medium.

Chapter 17

  • Electrolytes:

    • Compounds that conduct an electric current in aqueous solutions or the molten state.

      • Ex: ionic compounds

    • Strong Electrolytes:

      • Almost all of the solute exists as separate ions and conducts a strong current.

    • Weak Electrolytes:

      • Only a fraction of the solute exists as ions and conducts a weak current.

  • Nonelectrolytes:

    • Compounds that do not conduct an electric current in either the aqueous or molten states.

      • Ex: molecular compounds

Electrolyte vs nonelectrolyte

Electrolyte vs. Nonelectrolyte

Electrolytes conduct electricity

Non-electrolytes do not

Chapter 17

  • Water of hydration:

    • The water in a crystal or water of crystallization.

      • A compound containing water of hydration is a hydrate.

        • Ex: copper (II) sulfate pentahydrate

          • CuSO4ּ5H2O

  • Effloresce:

    • If a hydrate has a vapor pressure higher than that of the water vapor in the air, the hydrate will effloresce by loosing the water of hydration.

      • For simplicity sakes: if its humid, water stays with the compound and if it’s dry, the water evaporates.

    • Example: CuSO4ּ5H2O has a vapor pressure of 1.0 kPa. The water vapor at room temperature is ~1.3 kPa. Will the compound effloresce?

      • No, the vapor pressure is too high.

Drying agents

Drying Agents

  • Some compounds have a low vapor pressure and remove water from the air.

  • Hygroscopic:

    • Salts and other compounds that remove moisture from the air.

      • CaCl2

    • Hygroscopic substances are used as drying agents or desiccants.

      • Ex.: silica gel

    • Deliquescent compounds:

      • Remove sufficient water from the air to dissolve completely and form solutions.

        • Ex: NaOH and Damp Rid

Section 17 4

Section 17.4

  • Suspensions:

    • Mixtures from which particles settle out upon standing.

      • Ex.: sandy water

    • The particles are bigger than in solutions (100 x bigger)

    • Exhibits Tyndall Effect:

      • Scattering of light in all directions

    • Heterogeneous mixtures – 2 substances clearly identified.



  • Colloids:

    • Heterogeneous mixtures containing particles that are intermediate in size. They are between those of suspensions and true solutions. (between 1nm and 100nm)

    • Particles are the dispersed phase.

    • Spread throughout the dispersion medium. (they can be solids, liquids, or gases)

      • Ex.: glue, jello, paint, aerosol sprays, smoke, fog

Colloid cont

Colloid cont.

  • Cloudy or milky appearance when concentrated, but when dilute appear clear.

  • Exhibit the Tyndall Effect

  • Particles exhibit Brownian Motion:

    • Chaotic movement of colloidal particles

      • These movements are the result of bumping into water molecules and keeps them from settling out.

      • Ex: bumper cars

Tyndall effect

Tyndall Effect

Comparison table for solutions colloids and suspensions

Comparison Table for solutions, colloids and suspensions.



  • Emulsions:

    • Colloidal dispersions of a liquid in a liquid.

      • i.e. particles group together because of the same charge.

      • Ex.: oil in water

        • The soap and detergents are emulsifying agents (they cause an emulsion to form)


Polar end

Attracted to the water

Non polar end

Attracted to



Palmitic acid – used in making soaps

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