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Solubility. Polar Molecules and Solubility . Learning Goals. Students will understand that physical properties such as the polarity of molecules are related to a compound’s solubility. Students will be able to predict the solubility of compounds in water. Success Criteria.
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Solubility Polar Molecules and Solubility
Learning Goals • Students will understand that physical properties such as the polarity of molecules are related to a compound’s solubility. • Students will be able to predict the solubility of compounds in water
Success Criteria • Students will understand how intramolecular and intermolecular forces affect
Review: Polar Molecules • Compounds with covalent bonds usually form non-polar molecules since neither atom gains a positive or negative charge. • There is a small electronegativity difference between the atoms. • In some molecules, there are polar bonds, but the atom is symmetrical leading to an overall non-polar molecule.
Water (H2O) is the classic polar molecule. Oxygen has a higher electronegativity (3.5) than hydrogen (2.1). The electronegativity difference is 1.4 and a polar covalent bond forms. This means that the oxygen atom gains a negative charge and the hydrogen gains a positive charge. Water is a polar molecule. • A similar effect is seen in Hydrofluoric Acid, but carbon tetrachloride is symmetrical and is therefore non-polar! Water (H2O)
Which Molecules are Polar? • HCl • NH3 • BF3 • CCl4 • CH3Cl
Solutions - terminology • Solutions are homogenous mixturesof substances composed of at least one solute and one solvent • Homogenous mixture is a uniform mixture of only one phase • Solute is a substance that is dissolved in a solvent (e.g. NaCl) • Solvent is the medium in which a solute is dissolved; often the liquid component of a solution (e.g. water) • An aqueous solution is a solute dissolved in water (e.g. NH3(aq))
Solutions - terminology • Electrolyteis a compound that, in aqueous solution, conducts electricity • Nonelectrolyte is a compound that, in aqueous solution, does not conduct electricity • Acid is a substance that, in aqueous solution, turns blue litmus paper red • Base is a substance that, in aqueous solution, turns red litmus paper blue • Neutral is a substance that, in aqueous solution, has no effect on either red of blue litmus paper; neither acidic or basic
Solubility • Polar molecules only dissolve into polar liquids. For example, salt dissolves into water. • Salt (NaCl) is ionic and water is a polar molecule (polar covalent bonds)
Solubility • Non-polar molecules only dissolve into non-polar liquids • Grease dissolves in gasoline • Oil paint dissolves in paint thinner
Solubility • A solution is a homogeneous mixture of two substances. It is composed of a solvent (the substance that does the dissolving) and a solute (the substance that gets dissolved). • For example Kool Aid is a solution with the drink crystals being the solute and water being the solvent.
Solubility • Water dissolves Sodium Chloride, the polar water molecules surround the NaCl crystals and rip it apart! This causes the Ionic Crystal (NaCl) to Dissociate or Separate in Na+ ion and a Cl- ion. • In cases where water is the solvent, the solution is considered to be an aqueous solution. • Polar solutions conduct electricity. We call these solutions electrolytes.
Intermolecular Forces • Students will review concepts such as electronegativity, properties of matter and bonding. • Students will understand that intramolecular forces such as covalent bonding, polar covalent bonding and ionic bonding affect the solubility of a substance • Student will learn the terminology related solutions.
Predicting High and Low Solubilities (pp. 275-277) Highest Solubility - Acetic Acid and Methanol • Molecules are polar • Formation of hydrogen bonds with water molecules High Solubility - Dimethyl ether • Molecule is polar • Presence of oxygen atom means some hydrogen bonding with O-H ends of water molecules Slightly Soluble - Carbon dioxide and Oxygen • Should be non-polar, but oxygen presence means that there is a possibility of some hydrogen bonding with water molecules. Insoluble - Propane and Tetrachloromethane • Nonpolar molecules • Little or no solubility in water, cannot participate in dipole-dipole forces and hydrogen bonding
Miscibility • When a solute and a solventdo not mix, the solute is said to be insoluble. The solute and solvent are immiscible. • When the solvent and solute do mix they are soluble and miscible.
Miscibility • Why is it important to know about polar and non-polar molecules? • Polar molecules dissolve into other polar molecules • Non-polar molecules dissolve into other non-polar molecules but often not as easily! • BUT polar molecules do not dissolve non-polar molecules – they form mixtures. • LIKE DISSOLVES LIKE!
Miscibility • Oil and water do not mix. They are immiscible. (Oil is insoluble in water). Oil is non-polar and water is polar. • Salt dissolves in water. They are miscible. (Salt is soluble in water). • Both salt (NaCl) and water are polar molecules.
Colloids • Colloids are mixtures that look a lot like solutions. They are very fine particles that are non-polar and mix into other non-polar compounds and sometimes water. Whipped Cream Milk Mayonnaise Solid stick deodourant Jello
