Solutions: Solvents, Solutes, and Aqueous Solutions

1. Chapter 15“Solutions”

2. Solvents and Solutes • Solution - a homogenous mixture consisting of a solute dissolved in a solvent. • Solvent- the dissolving medium • Solute -the dissolved particles • Aqueous solution- a solution with water as the solvent.

3. Parts of a Solution: 1. Solute A solute is the dissolved substance in a solution. Salt in salt water Sugar in soda drinks Carbon dioxide in soda drinks 2. Solvent A solvent is the dissolving medium in a solution. Water in salt water Water in soda

4. Aqueous Solutions • Water dissolves ionic compounds and polar covalent molecules best. • The rule is: “like dissolves like” • Polar dissolves polar. • Nonpolar dissolves nonpolar. • Oil is nonpolar. • Oil and water don’t mix. • Salt is ionic- makes salt water.

5. Liquids • Miscible means that two liquids can dissolve in each other • water and antifreeze • water and ethanol • Partially miscible- slightly • water and ether • Immiscible means they can’t • oil and vinegar

6. The Solution Process • Called “solvation”. • Water breaks the + and - charged pieces apart and surrounds them. • In some ionic compounds, the attraction between ions is greater than the attraction exerted by water • Barium sulfate and calcium carbonate

7. H H H H O O O H H H H O O H H O O H H H H H H O H O H How Ionic solids dissolve in water These ions have been pulled away from the main crystal structure by water’s polarity. These ions have been surrounded by water, and are now dissolved!

8. Solids will dissolve if the attractive force of the water molecules is stronger than the attractive force of the crystal. • If not, the solids are insoluble. • Water doesn’t dissolve nonpolar molecules (like oil) because the water molecules can’t hold onto them. • The water molecules hold onto other water molecules, and separate from the nonpolar molecules. • Nonpolars? No repulsion between them

9. Electrolytes and Nonelectrolytes • Electrolytes- compounds that conduct an electric current in aqueous solution, or in the molten state • all ionic compounds are electrolytes because they dissociate into ions (they are also called “salts”) • barium sulfate- will conduct when molten, but is insoluble in water!

10. Electrolytes and Nonelectrolytes • Do not conduct? = Nonelectrolytes. • Most are molecular materials, because they do not have ions • Not all electrolytes conduct to the same degree • there are weak electrolytes, and strong electrolytes • depends on: degree of ionization

11. - + - - + + acetic acid salt sugar Electrolyte Conductivity Non- Electrolyte Weak Electrolyte Strong Electrolyte solute exists as ions and molecules solute exists as ions only solute exists as molecules only DISSOCIATION IONIZATION View animation online.

12. Electrolytes and Nonelectrolytes • Strong electrolytes exist as nearly 100 % ions • Weak electrolytes have only a fraction of the solute that exists as ions

13. Mixtures that are NOT Solutions • Suspensions: mixtures that slowly settle upon standing. • Particles of a suspension are greater in diameter than 1000 nm. • Can be separated by filtering • Colloids: heterogeneous mixtures with particles between the size of suspensions and true solutions (1-1000 nm)

14. Mixtures that are NOT Solutions • The colloid particles are the dispersedphase, and are spread throughout the dispersion medium • The first colloids were glues. Others include mixtures such as gelatin, paint, aerosol sprays, and smoke

15. Mixtures that are NOT Solutions • Many colloids are cloudy or milky in appearance when concentrated, but almost clear when dilute • do not settle out • can not be filtered out • Colloids exhibit the Tyndall effect- the scattering of visible light in all directions. • suspensions also show Tyndall effect

16. Colloids and suspensions scatter light, making a beam visible, due to their large particle size. Solutions do not scatter light, because of their small particle size. The Tyndall Effect colloid solution Which glass contains a colloid?

17. - Page 461 Note that you can easily see the “sunbeam”, probably due to the presence of fog in the forest

18. How Much? • Solubility- is the maximum amount of substance that will dissolve at a specific temperature (the units for solubility are: g solute/100 g solvent) • Saturated solution- Contains the maximum amount of solute dissolved. NaCl = 36.0 g/100 mL water • Unsaturated solution- Can still dissolve more solute (for example 28.0 g NaCl/100 mL) • Supersaturated- solution that is holding more than it theoretically can; a “seed crystal” will make it come out

19. Saturation and Equilibrium Saturation equilibrium established Solute is dissolving More solute is dissolving, but some is crystallizing

20. Concentration is... • a measure of the amount of solute dissolved in a given quantity of solvent • Aconcentrated solution has a large amount of solute • Adilute solution has a small amount of solute • These are qualitative descriptions • But, there are ways to express solution concentration quantitatively

21. Concentrated vs. Dilute

22. Molarity • Molarity = moles of solute liters of solution • Abbreviated with a capital M, such as 6.0 M • This is the most widely used concentration unit used in chemistry.

23. Molality • Molality = moles of solute kilograms of solvent • Abbreviated with a small case m, such as 6.0 m • This corrects volume–related concentration changes due to temperature.

24. Mole Fraction • Mole Fraction = moles of solutemoles solvent + moles solute X = nsolute nsolute+ nsolvent • This is can be thought of as a percent