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Water Solutions & Colligative Properties

Water Solutions & Colligative Properties. Definitions: solutions. A solution is a HOMOGENEOUS mixture of 2 or more substances mixed evenly at molecular level.. One part is regarded as the SOLUTE and the others as SOLVENT. Parts of a Solution.

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Water Solutions & Colligative Properties

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  1. Water Solutions& Colligative Properties

  2. Definitions:solutions A solution is a HOMOGENEOUSmixture of 2 or more substances mixed evenly at molecular level.. One part is regarded as the SOLUTEand the others as SOLVENT

  3. Parts of a Solution • SOLUTE –material being dissolved (usually the lesser amount) • SOLVENT– material doing the dissolving (usually the greater amount) • Solute + Solvent = Solution

  4. moles solute ( M ) = Molarity liters of solution Concentration of Solute The amount of solute in a solution is given by its concentration.

  5. 1.0 L of water was used to make 1.0 L of solution. Notice the water left over.

  6. moles solute m of solution = kilograms solvent Another Concentration Unit: Add MOLALITY, m

  7. Concentration Units x 100% mass of solute x 100% = mass of solution mass of solute mass of solute + mass of solvent % mass (Percent by Mass) The concentration of a solution is the amount of solute present in a given quantity of solvent or solution. % by mass =

  8. II. Types of Solutions Ionic Solutes Molecular Solutes Definition:Solubility measures the maximum amount of solute that can be dissolved in a solvent at a given temperature (measures maximum concentration)

  9. K+(aq) + MnO4-(aq) IONIC Solutes 1. Most are HIGHLY soluble EX.KMnO4 = a handful can be dissolved in a teaspoon of water. aqueous solutions. KMnO4 in water

  10. 2.Dissolves in Water as Ions can conduct electricity Water solvent molecules attach to the ions (H end to the Cl-, O end to the Na+) Water solvent holds the ions apart and keeps the ions from coming back together

  11. Hydration of IONS Na+1Cl-1H2O Na+1 Cl-1 H2O shape = + - The polar ends of water surround the charged ions in the solid, neutralizing the charges allowing ions to move freely.

  12. Fig 10-34 Olmsted Williams • Interaction that helps a solid ionic crystal dissolve in water. • The arrows indicate ion-dipole interactions.

  13. B. MolecularSolutes (covalent compounds) • Most are INSOLUBLE (not soluble/ can’t bedissolved) • They do not have + or – for water to surround

  14. B. MolecularSolutes(covalent compounds) 2. SOME are very soluble. a. Polar molecules with OH bonds. (alcohols & sugars b. Acids (Have “H” in front) water grabs “H” forming hydronium acid HOH + HCl  HOH + Cl-1 H+1 Examples include: sugar ethanol ethylene glycol

  15. moles of solute liters of solution moles of solute m = mass of solvent (kg) M = C. Concentration of solutions (Molarity and Molality) Molarity(M) Molality(m) 12.3

  16. Molarity (M) = • Molality (m) = • Molarity is a temperature-dependent scale because volume (and density) change with temperature. • Molality is a temperature-independent scale because the mass of a kilogram does not vary with temperature.

  17. Molarity (M) = moles of solute Liters of solution M = mole A L solution EX:1. 75.0 grams of calcium chloride are dissolved in enough water to make 750. mL of solution. What is the molarity of this solution? *Remember* 1L = 1000mL = 0.901 M

  18. Molality (m) = moles solute kg solvent m = mole A kg B *Remember* 1g = 1mL for H2O 1000g = 1 kg Ex: What is the molality of a solution if 4.8gNaCl is dissolved in 500 ml of H20? = 0.164 m

  19. Molarity & Dilution of Solution • M1V1 = M2V2 • MConVCon = MdiluteVdilute

  20. Electrolyte Particles (i = ?) 1. Identification of “swimmers” in an aqueous solution • IMPORTANT – the colligative properties of freezing point and boiling point are proportional to the number of particles present in the solution. • particles, i • CaCl2 Ca+2 (aq) + 2 Cl –1 (aq) Ionic :i = 3 • CH3OH4 CH3OH4 (aq) Covalent: i=1 • H2SO4 2 H+1 + SO4 -2 Acids: i = 3 • Al2(SO4)3i = 5

  21. Review Colligative Properties A property that depends on the concentration of solute particles but not the identity of the solute Vapor Pressure Reduction Boiling Point Elevation Freezing Point Depression

  22. Freezing of a solvent Solvent Particles start to freeze Frozen Solvent

  23. Structure of Ice

  24. Freezing of a Solution Water with solute added Particles begin to freeze Solid formed

  25. Freezing Points

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