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Unit 4: Solutions & Solubility. 6.1/6.2 Defining and Explaining Solutions. Solutions: a definition. a type of mixture m ixtures can be separated by non-chemical means such as filtration, heating, or centrifugation a homogeneous mixture t he mixture is the same all the way through
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Unit 4: Solutions & Solubility 6.1/6.2 Defining and Explaining Solutions
Solutions: a definition • a type of mixture • mixtures can be separated by non-chemical means such as filtration, heating, or centrifugation • a homogeneous mixture • the mixture is the same all the way through • does not settle out if left to sit, whereas most heterogeneous mixtures do
The Parts of a Solution • Solute = a substance that is dissolved in a solvent (e.g. salt, NaCl, in saltwater) • Solvent = the medium in which a solute is dissolved; often the liquid component of a solution (e.g. water, in saltwater) • in a solution, there is more solvent than solute
Classifying Solutions • Types of Solutions: • Electrical Conductivity • Electrolyte • Nonelectrolyte • The state of their solute and solvent • gas solute in gas solvent (eg. air) • Solid solute in liquid solvent (eg. saltwater) • pH (Acid, Base or Neither) • Acidic • Basic • Neutral
Conductivity • Electrolyte = a compound that, in an aqueous solution (water is the solvent), conducts electricity • Mostly ionic compounds • Nonelectrolyte = a compound that, in an aqueous solution, does not conduct electricity • Mostly molecular compounds
pH • Acid = a substance that, in aqueous solution, turns litmus paper red (pH is less than 7) • Base = a substance that in an aqueous solution, turns litmus paper blue (pH is greater than 7) • Neutral = a substance that, in aqueous solution, has no effect on either red or blue litmus paper; neither acidic nor basic (pH = 7)
Unit 4: Solutions & Solubility 6.2 Explaining Solutions
Explaining Solutions • Why do only some chemicals dissolve in water? Why are some chemicals mutually attracted to one another? Recall: • Intermolecular Forces = an attraction between molecules
Polarity and Solubility • Polar substances dissolve in polar solvents • Polar solute molecules are surrounded and suspended in solution by polar solvent molecules (see handout) • Non-polar substances dissolve in non-polar solvents • In other words: • like-polarity substances dissolve in each other (“like dissolves like”)
Explaining Non-aqueous Mixtures • London Dispersion forces are weak intermolecular forces responsible for non-polar substances dissolving in non-polar solvents
Recall: Hydrogen Bonding • a relatively strong dipole-dipole force between a solute with N, O, or F lone pairs or with a H-N, H-O, or H-F bond and water • when multiple hydrogen bonds between solute and solvent is possible, we would expect an especially high solubility (see handout)
Ionic Compounds in Water • More ionic compounds dissolve in water than in any other known solvent… • Ionic compounds dissociate into individual aqueous ions (see handout) • Dissociation = the separation of ions that occurs when an ionic compound dissolves in water (see handout)
Predicting Solubility: Group Activity • Rank the molecular compounds from greatest to least solubility in water and explain your prediction. • Hint: examine the Lewis structures carefully and consider the type of intermolecular bond (LF, D-D or H-B) that it forms with water. • Also, consider the possibility of multiple hydrogen bonds.
Homework: • Read pg. 268 - 279 • Do #3, 5 on pg. 277 • Do #7, 9 – 11 on pg. 279
