1. Chapter 13 Section 4 Solutions: Physical Properties of Solutions Ridgewood High School scasatelli@ridgewood.k12.nj.us

2. A Water Molecule Water is a unique tri-atomic compound  Consists of two hydrogen atoms and one oxygen atom Found through out the planet in different forms  Ice, snow, rain, vapor Water is a polar molecule

3. Properties of A Water Molecule High surface tension Low vapor pressure High specific heat capacity High heat of vaporization High boiling point Water molecules are attracted to one another by hydrogen bond interactions

4. Water’s Surface Properties Surface of water is similar to skin Surface Tension: that is explained by water’s ability to form hydrogen bonds.  Water molecules at the surface tend to be drawn into the body of the liquid.  The inward force or pull that trends to minimize the surface area of the liquid is called SURFACE TENSION

5. Surface Tension The higher the surface tension the more spherical is the drop of liquid. A liquid that has high surface tension has high intermolecular forces between the molecules.

6. Surfactant Surfactant: a technique used to decrease a liquids surface tension.  A surfactant is a wetting agent such as soap or detergent  The soap or detergent molecules interfere with the hydrogen bonding between water molecules.  Result: water does not bead, but instead collapses and flattens out.

7. Water’s Vapor Pressure Vapor pressure of a liquid is caused by molecules that escape the surface of the liquid and enter the gas phase. Water molecules are held tightly together by hydrogen bonds, therefore the tendency for these water molecules to escape is low. What would happen if this was not a property of water?

8. Specific Heat Capacity It takes 4.18J of heat energy to raise the temperature of 1g of water 1 degree C.  Above is the specific heat capacity of water  Because of hydrogen bonding the specific heat capacity of water is higher than most other substances.  Waters high specific heat capacity helps moderate air temperature around large bodies of water.

9. 17.2 Water Vapor and Ice Why does solid water float in liquid water?

10. Evaporation/Vaporization Water absorbs a large amount of heat as it evaporates or vaporizes Heat of Vaporization: is the amount of energy needed to convert 1g of a substance from a liquid to a gas at the boiling point.  An extensive network of hydrogen bonds tightly holds the molecules in liquid water together.  These bonds must be broken before water changes from the liquid to the vapor state.

11. Condensation The reverse of vaporization is condensation. When 1g of steam at 100°C condenses to 1g of liquid water at 100°C, 2.26kJ of heat is given off. Heat of condensation is equal to the heat of vaporization

12. Ice and Solid Liquids H 2 O Characteristics Water cools it contracts slightly and it’s density gradually increases until temp is 4°C. Below 4° C, however, the density of water starts to decrease. Ice forms at 0°C, has about 10% greater volume and a lower density. Ice therefore floats. Normal Liquids Liquid cools, slightly contracts. Density increases because its volume decreases while its mass stays constant. Cooling continues, the liquid becomes solid The density of a solid is normally greater then its corresponding liquid, the solid sinks in its own liquid.

13. Liquid and Solid H 2 O

14. 17.3 Aqueous Solutions Aqueous Solution: water samples containing dissolved substances. Solution: made up of solvent and solute  Solvent: the dissolving medium  Solute: the dissolved particles

15. Water as a Solvent Substances that dissolve the best in water are:  Ionic compounds  Polar covalent compounds Non-polar covalent molecules do not dissolve in water  Methane  Oil  grease

16. The Solution Process Water molecules are in continuous motion because of their kinetic energy. When a crystal of sodium chloride is placed in water, the water molecules collide with it. Solvation: the process that occurs when a solute dissolves.  The negatively and positively charged ions become solvated, they become surrounded by solvent molecules.

17. The Rule “Like dissolves Like” Both oil and gasoline are composed of non- polar molecules.  They form a solution, because there are no repulsive forces between them. RULE: polar solvents dissolve ionic compounds and polar molecules; non-polar solvents dissolves non-polar compounds

18. Conductivity Conductivity: substances that can conduct electricity  Based on if the particles are charged and if the particles are moving.  Is solid NaCl conductive? NO…solid NaCl is not conductive because the ions Na + and Cl - cannot move in the solid state.  Is aqueous NaCl condcutive? YES…aqueous NaCl is conductive because the particles are charged and are moving.

19. Conductivity: Electrolytes Where have you heard the term electrolytes? What are electrolytes?  Electrolytes are substances that dissolve in liquid solvents and provide ions that conduct electricity.  Your body requires salts…after strenuous activity those salts need to be replenished.

20. Electrolytes and Nonelectrolytes Electrolytes: compounds that conduct an electric current in aqueous solution or the molten state.  All ionic compounds are electrolytes.  Electrolytes conduct electricity in solution and in the molten state. Nonelectrolytes: compounds that do not conduct an electric current in either aqueous solution or the molten state.  Some very polar molecules are nonelectrolyltes until it is dissolved in water.

21. Weak and Strong Electrolytes Weak Electrolyte: only a fraction of the solute exists as ions. Strong Electrolyte: almost all the solute exists as separate ions. Table 17.3 in Text book

22. Electrolytes: Strong and Weak Strong Electrolytes  Compounds that completely dissociate in solution  Meaning…the ions are completely seperated in solution…Na + Cl - ions in water.  Strong conductors of electricity Weak Electrolytes  Do not completely dissociate in solution.  Weak conductors of electricity.

23. Water of Hydration Water molecules are an integral part of the crystal structure of many substances. Water of Hydration or water crystallization: is water in a crystal  A compound that contains water of hydration is called a hydrate.  They contain fixed quantities of water and have definite compositions.  Table 17.4 textbook-common hydrates

24. Water of Hydration Forces holding the water molecules in hydrates are not strong  Water is easily lost and regained Hydrates have an estimated vapor pressure.  If hydrate has a vapor pressure higher than that of the water vapor in air, the hydrate will effloresce by losing the water of hydration.  Hygroscopic: are hydrated salts that have a low vapor pressure that remove moisture from the air.

25. Desiccants and Deliquescent Desiccants: are hygroscopic substances that are used as drying agents.  Ex: silica gel Deliquescent: these compounds remove sufficient water from the air to dissolve completely and form solutions.  Ex: sodium hydroxide  Deliquescence occurs when the solution formed has a lower vapor pressure than that of the water in the air.

26. 17.4: Heterogeneous Aqueous Systems Suspensions: mixtures from which particles settle out upon standing  A suspension differs from a solution because the component particles of a suspension are much larger. Suspension particle size 100nm Solution particle size 1nm  Suspensions are heterogeneous because at least two substances can be clearly identified.

27. Heterogeneous Aqueous Systems Collids: are heterogeneous mixtures containing particles that are intermediate in size between those of suspensions and true solutions.  Range in size from 1nm to 100nm.  The particles spread throughout the dispersion medium, which can be a solid, liquid or gas.  Ex: Glue, gelatin desserts, paint, aerosol sprays and smoke.  Table 17.5

28. Tyndall Effect Tyndall Effect: is the scattering of visible light in all directions.  Colloidal particles exhibit this effect  A beam of light passes through a colloid like a sunbeam in a dusty room.  Suspensions also exhibit the Tyndall Effect

29. Brownian Motion Brownian Motion: chaotic movement of colloidal particles  Caused by collisions of water molecules of the medium with the small, dispersed colloidal particles.  Collisions prevented the particles from settling at the bottom.  Particles can also become charged, all the particles in a particular colloidal system will have the same charge The repulsion of like-charged particles prevents the particles also from settling at the bottom

30. Brownian Motion

31. Emulsions Emulsions: they are colloidal dispersions of liquids in liquids. Emulsifying agents allow the formation of colloidal dispersions between liquids that do not ordinarily mix.  An emulsifying agent is important for formation of an emulsion and for maintaining the emulsion’s stability  Ex: oil and grease are not soluble in water, they will form colloids when soap or detergent is added to the water.  Soap and detergent act as an emulsifying agent