Solutions

1. Solutions Aqueous Solutions

2. Review • How do ionic and molecular compounds differ? • The molecules in molecular compounds are electrically neutral, covalently bonded groups of atoms that behave as a unit. Ionic compounds are huge collections of cations and anions.

3. Reivew • What is a cation? • A positive ion • What is an anion? • A negative ion • Why are ionic compounds generally soluble in water? • The cations and anions are attraced to the charged end of polar H2O molecules.

4. Solvents and Solutes • Aqueous solution: • A solution in which the solvent is water • Solvent: • The dissolving medium in a solution • Solute: • The dissolved particles in a solution

5. Solvents and Solutes • What are some of the properties of solutions? • They are stable (they don’t settle out over time) • Particles/ion are less than 0.1 nanometers in diameter • They cannot be separated by filtration

6. The Solution Process • Solvation: • A process that occurs when an ionic solute dissolves • In solution, the ions are surrounded by solvent molecules • What is meant by “like dissolves like?” • This refers to the polarity of the compounds

8. Electrolytes and Nonelectrolytes • Electrolytes: • A compound that conducts an electrical current in aqueous solution or in the molten state • All ionic compounds are electrolytes, but most covalent compounds are not • Some polar covalent compounds form polyatomic ions when dissolved in water • These compounds are electrolytes

9. Electrolytes and Nonelectrolytes • Nonelectrolytes: • A compound that does not conduct an electric current in aqueous solution or in the molten state • Weak electrolytes: • A solution in which only a fraction of the solute exists as ions. • Strong electrolytes: • A solution in which a large portion of the solute exists as ions.

10. Water of Hydration • Water of hydration: • Water molecules that are an integral part of a crystalline structure • Written as (ionic formula unit)·#H2O • The # tells you how many water molecules per ionic formula unit • If the water is there it is called a hydrate. If the water is not there (when it usually is) it is called the anhydrate. The two forms often have different colors.

11. Water of Hydration • Effloresce: • To lose the water of hydration • Hydroscopic: • A term describing compounds that remove water from the air • Dessicant: • A hydroscopic substance used as a drying agent • Deliquescent: • A term describing a substance that removes enough water from the air to form a solution

12. Water of Hydration • You can use the formula of a a hydrate to calculate its percent by mass water.

13. Water of Hydration • Example: Calculate the percent mass of water in Epsom salt, MgSO4·7H2O

14. Heterogeneous Aqueous Solutions • What is a heterogeneous mixture? • One with different parts, like sand in water

15. Suspensions • Suspensions: • A mixture from which some of particles settle out slowly upon standing • Muddy water • The particles are about 100 nm in diameter and can be filtered out

16. Colloids • Colloid: • A mixture whose particles are intermediate in size between those of a suspension and a solution • These cannot be filtered • Jello is a colliod.

17. Colloids • Dispersed phase: • The particles in a colloid • Usually between 0.1 nm and 100 nm in diameter • Dispersing medium: • The substance a colloid is made in

18. Colloids • Tyndall effect: • Scattering of light by particles in a colloid or suspension, which causes the beam to become visible • Brownian motion: • The chaotic movement of colloidal particles, caused by collision with particles of the dispersing medium

19. Colloids • Emulsions: • Colloids of liquids in liquids (like shaking oil and vinegar to mix them together) • Adding an emulsifier makes the emulsion stable • Add flour to oil and water to make gravy • Add parmesan cheese to butter and cream to make Alfredo sauce • Add egg yolk to oil and vinegar to make mayonnaise