Resolving Dissolving p. 119

Entry Task Look at your data from the Particular Properties Lab. Why do you think that all of the substances that were very soluble in water were also strong conductors?

Resolving Dissolving Create a new title/thread “Resolving Dissolving” and date:11/12/13 Cool! Learning Target: I can explain why some substances dissolve in water and others do not. Update your Table of Contents!

Resolving Dissolving Read the intro on p. 119 Put your work under Process & Procedure p. 119 Read “Solvation Process” p Take notes Remember to include a summary at the end! Do P&P #2 on page 122!

Resolving Dissolving All matter demonstrates electrical properties Means that all matter is made up of plus and minus charges But… not all matter demonstrates electrical properties in the same way! Why do certain substances dissolve in water? Because they have similar electrical properties

Resolving Dissolving From particular properties, the salts (hard crystalline solids with high melting points and high conductivity in solution) dissolve in water. They dissolve in water because they have similar electrical properties. Oils and wax have low melting points and do not conduct electricity. They do not dissolve in water because they have different electrical properties.

Resolving Dissolving Ions are charged particles. Solids made of ions are called ionic compounds.

Resolving Dissolving Solid sodium chloride is made up of ions. Positive Sodium Ions (Na + ) and negative Cloride Ions (Cl - ) Because the ions have opposite charges, they are attracted to each other. This attraction keeps them locked in place – the structure is called a crystal lattice. Since the ions in a solid are not free to move around, a solid ionic compound cannot conduct electricity.

Resolving Dissolving Ionic compounds can dissolve in water because water is polar Water has a dipole (a positive end and a negative end in the same molecule). The negative end of a water molecule will attract Na + The positive end of a water molecule will attract Cl - This attraction is enough to pull the ions free from the crystal lattice.

Resolving Dissolving Once the ions are free of the crystal lattice, they are surrounded by water molecules. The process of water interacting with ions and dissolving an ionic compound is called solvation. The ions (charged particles) can move freely, which is why ionic compounds can conduct electricity in solution

Resolving Dissolving General rule: substances with similar electrical properties to water molecules will dissolve in water. “Like dissolves like”

Resolving Dissolving Why doesn’t baby oil and wax dissolve in water? Because they have different electrical properties than water! There are no dipoles in wax or baby oil (no sections of plus and minus charge). These are non-polar molecules. Baby oil and wax are covalent molecules The plus and minus charges are equally distributed over the whole molecule, so there are no dipoles.

Resolving Dissolving Ionic compounds: Polar molecules: Non-polar molecules:

Resolving Dissolving P&P #2: Why does paraffin (wax) NOT dissolve in water?

Resolving Dissolving Read “Other Polar Covalent Molecules” p Take notes Remember to include a summary at the end! Do R&C #1-3 on page !