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Unit 4: Solutions & Solubility 6.1/6.2 Defining and Explaining Solutions.

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Presentation on theme: "Unit 4: Solutions & Solubility 6.1/6.2 Defining and Explaining Solutions."— Presentation transcript:

1 Unit 4: Solutions & Solubility 6.1/6.2 Defining and Explaining Solutions

2 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

3 Homogenous vs. Heterogeneous

4 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

5 Solutions

6 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

7 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

8 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)

9 Unit 4: Solutions & Solubility 6.2 Explaining Solutions

10 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

11 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”)

12 Explaining Non-aqueous Mixtures  London Dispersion forces are weak intermolecular forces responsible for non- polar substances dissolving in non-polar solvents

13 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)

14 Hydrogen Bonds between water molecules

15 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)

16 Ionic Compounds in Water


18 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.

19 Homework:  Read pg  Do #3, 5 on pg. 277  Do #7, 9 – 11 on pg. 279

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