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SURVEY OF CHEMISTRY I CHEM 1151 CHAPTER 7

SURVEY OF CHEMISTRY I CHEM 1151 CHAPTER 7. DR. AUGUSTINE OFORI AGYEMAN Assistant professor of chemistry Department of natural sciences Clayton state university. CHAPTER 7 SOLUTIONS AND COLLOIDS. SOLUTION. - A homogeneous mixture of two or more substances Solvent

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SURVEY OF CHEMISTRY I CHEM 1151 CHAPTER 7

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  1. SURVEY OF CHEMISTRY I CHEM 1151 CHAPTER 7 DR. AUGUSTINE OFORI AGYEMAN Assistant professor of chemistry Department of natural sciences Clayton state university

  2. CHAPTER 7 SOLUTIONS AND COLLOIDS

  3. SOLUTION - A homogeneous mixture of two or more substances Solvent - The substance present in the greatest quantity Solute - The other substance(s) dissolved in the solvent

  4. SOLUTION - Solutions can exist in any of the physical states Solid Solution - dental fillings, metal alloys (steel), polymers Liquid Solution - sugar in water, salt in water, wine, vinegar Gas Solution - air (O2, Ar, etc. in N2), - NOx, SO2, CO2 in the atmosphere

  5. SOLUBILITY - A measure of how much of a solute can be dissolved in a solvent at a given temperature - Units: grams/100 mL Example Solubility of sugar in water at 20 oC is 204 g/100 mL H2O Three factors that affect solubility - Temperature - Pressure - Polarity

  6. SOLUBILITY Unsaturated Solution - More solute can still be dissolved at a given temperature Saturated Solution - No more solute can be dissolved at a given temperature Supersaturated Solution - Too much solute has temporarily been dissolved (more than solute solubility) Precipitate - Solute (solid) that falls out of solution

  7. PROPERTIES OF SOLUTIONS - A solution contains a solvent and one or more solutes - The ratio of solute to solvent may vary in a solution - Solution properties change with solute to solvent ratio - The dissolved solutes are present as individual particles (ions, atoms, or molecules) - Solutes remain uniformly distributed throughout the solution - Solutes are separated by physical means (evaporation, distillation)

  8. AQUEOUS SOLUTION - A solution in which water (H2O) is the solvent NaCl solution: solvent is H2O and solute is NaCl Hydrophilic - Substances that dissolve in water - Water loving (NaCl) - Usually polar substances Hydrophobic - Substances that do not dissolve well in water - Water fearing (hydrocarbons) - Usually nonpolar substances

  9. AQUEOUS SOLUTION - Ions make aqueous solutions good conductors of electricity - Solution conductivity indicates the presence of ions

  10. AQUEOUS SOLUTION Ionic Compounds - Form ions in aqueous solution (dissociate into component ions) Example - NaCl solution contains Na+ and Cl- ions NaCl(aq) → Na+(aq) + Cl-(aq) - Each ion is surrounded by water molecules - Good conductor of electricity

  11. AQUEOUS SOLUTION Solvation Process - Ions in aqueous solution are surrounded by the H2O molecules - The O atom in each H2O molecule has partial negative charge (δ-) - Attract positive ions - The H atoms have partial positive charge (δ+) - Attract negative ions - Cations and anions are prevented from recombining - Ions disperse uniformly throughout the solution (homogeneous)

  12. AQUEOUS SOLUTION Molecular Compounds - Most molecular compounds do not form ions in aqueous solution - The molecules disperse throughout the solution - Molecules are surrounded by H2O molecules Example - Sucrose solution contains neutral sucrose molecules - Each molecule is surrounded by water molecules - Poor conductor of electricity - A few molecular compounds form ions in aqueous solution - HCl dissociates into H+(aq) and Cl-(aq) - HNO3 dissociates into H+(aq) and NO3-(aq)

  13. NONAQUEOUS SOLUTION - A solution in which another substance other than water is the solvent Examples Alcohol petroleum ether Pentane Carbon tetrachloride

  14. RATE OF DISSOLUTION The rate at which solutes dissolve can be increased by - Grinding or crushing solute particles (size reduction) - Heating - Stirring or agitation

  15. CONCENTRATION OF SOLUTIONS - The amount of solute dissolved in a given quantity of solvent or solution Percent Concentration - Percent by mass [mass-mass percent, %(m/m)] mass of solution = mass of solute + mass of solvent

  16. CONCENTRATION OF SOLUTIONS A sugar solution is made by dissolving 5.8 g of sugar in 82.5 g of water. Calculate the percent by mass concentration of sugar.

  17. CONCENTRATION OF SOLUTIONS - The amount of solute dissolved in a given quantity of solvent or solution Percent Concentration - Percent by volume [volume-volume percent, %(v/v)] volume of solution ≠ volume of solvent + volume of solute - Due differences in bond lengths and angles

  18. CONCENTRATION OF SOLUTIONS Calculate the volume percent of solute if 345 mL of ethyl alcohol is dissolved in enough water to produce 1257 mL of solution

  19. CONCENTRATION OF SOLUTIONS - The amount of solute dissolved in a given quantity of solvent or solution Percent Concentration - Mass-volume percent [%(m/v)] - Units are specified because they do not cancel

  20. CONCENTRATION OF SOLUTIONS The concentration of a solution of NaCl is 0.92 %(m/v) used to dissolve drugs for intravenous use. What is the amount, in grams, of NaCl needed to prepare 41.50 mL of the solution? g solute = [%(m/v)] x [volume of solution (mL)]/[100 %] = [(0.92 % g/mL) x (41.50 mL)]/(100 %) = 0.38 g

  21. CONCENTRATION OF SOLUTIONS Molarity (M: molar) - The number of moles of solute per liter of solution - A solution of 1.00 M (read as 1.00 molar) contains 1.00 mole of solute per liter of solution

  22. CONCENTRATION OF SOLUTIONS • Calculate the molarity of a solution made by dissolving 2.56 g • of NaCl in enough water to make 2.00 L of solution • - Calculate moles of NaCl using grams and molar mass • Convert volume of solution to liters • - Calculate molarity using moles and liters

  23. CONCENTRATION OF SOLUTIONS After dissolving 1.56 g of NaOH in a certain volume of water, the resulting solution had a concentration of 1.60 M. Calculate the volume of the resulting NaOH solution - Convert grams NaOH to moles using molar mass - Calculate volume (L) using moles and molarity

  24. CONCENTRATION OF SOLUTIONS Mole Fraction - Fraction of moles of a component of solution

  25. CONCENTRATION OF SOLUTIONS Given that the total moles of an aqueous solution of NaCl and other solutes is 1.75 mol. Calculate the mole fraction of NaCl if the solution contains 4.56 g NaCl.

  26. DILUTION Consider a stock solution of concentration M1 and volume V1 If water is added to dilute to a new concentration M2 and volume V2 moles before dilution = moles after dilution M1V1 = M2V2 Calculate the volume of 3.50 M HCl needed to prepare 500.0 mL of 0.100 M HCl (3.50 M)(V1) = (0.100 M)(500.0 mL) V1 = 14.3 mL

  27. CHEMICAL ANALYSIS • Calculate the concentration of NaOH solution if 24.50 mL of this • base is needed to neutralize 12.00 mL of 0.225 M HCl solution • - Write balanced equation and determine mole ratio • - Calculate moles of HCl (convert mL to L) • - Determine moles of NaOH • Calculate molarity of NaOH

  28. CHEMICAL ANALYSIS NaOH + HCl → NaCl + H2O 1 mole NaOH : 1 mole HCl Volume HCl = 12.00 mL = 0.01200 L mole HCl = 0.225 M x 0.01200 mL = 0.00270 mol = mole NaOH

  29. CHEMICAL ANALYSIS • How many grams of KOH are needed to neutralize 25.00 mL of • 0.250 M H2SO4 solution • - Write balanced equation and determine mole ratio • - Calculate moles of H2SO4 • - Determine moles of KOH • - Calculate grams of KOH using molar mass

  30. CHEMICAL ANALYSIS 2KOH + H2SO4 → K2SO4 + 2H2O 2 mole KOH : 1 mole H2SO4 mole H2SO4 = 0.250 M x 0.02500 L = 0.00625 mol Mole KOH = 2 x 0.00625 mol = 0.0125 mol

  31. ELECTROLYTES - Substances whose aqueous solutions contain ions NaCl(aq) → Na+(aq) + Cl-(aq) - Two categories: strong and weak electrolytes Strong Electrolytes - Solutes that completely or nearly completely ionize when dissolved in water Salts: NaCl, NH4Cl, KBr, NaNO3 Strong acids: HCl, HNO3, H2SO4 Strong Bases: NaOH, KOH, Ca(OH)2

  32. ELECTROLYTES - Substances whose aqueous solutions contain ions NaCl(aq) → Na+(aq) + Cl-(aq) - Two categories: strong and weak electrolytes Weak Electrolytes - Only a small fraction of solutes ionize when dissolved in water (exhibit a small degree of ionization) Weak acids: acetic acid (HC2H3O2), citric acid (C6H8O7) Weak bases: ammonia (NH3) methylamine, cocaine, morphine

  33. ELECTROLYTES - Single arrow is used to represent ionization of strong electrolytes H2SO4(aq) → H+(aq) + HSO4-(aq) - Ions have no tendency of recombining to form H2SO4 - Double arrow is used to represent ionization of weak electrolytes HC2H3O2(aq) ↔ H+(aq) + C2H3O2-(aq) - This implies reaction occurs in both directions - Chemical equilibrium is when there is a balance in both directions

  34. NONELECTROLYTES - Substances whose aqueous solutions do not contain ions Examples Many molecular compounds Sucrose (C12H22O11) ethanol (C2H5OH)

  35. COLLIGATIVE PROPERTIES - Physical properties of a solvent changes when a solute is added - Four physical properties change based on the amount of solute added but not the solute’s chemical identity - These are known as the Colligative Properties - Vapor-pressure lowering - Boiling-point elevation - Freezing-point depression - Osmotic pressure

  36. COLLIGATIVE PROPERTIES Osmolarity (osmol) = (M) x (i) i = number of particles produced from the dissociation of one formula unit of solute - The number of particles present determines the osmotic pressure - NaCl dissociates in solution to produce 2 particles (Na+ and Cl-) - Glucose does not dissociate - The osmotic pressure of NaCl is twice that of glucose - Solutions with higher osmotic pressure take up more water than solutions with lower osmotic pressure

  37. COLLOIDAL DISPERSION - A substance is dispersed in another substance but not dissolved (typically cloudy) - Dispersed particles are intermediate in size between those of a true solution and an ordinary heterogeneous mixture - Dispersed phase is used in place of solute - Dispersing medium is used in place of solvent Examples Blood, milk, smoke, fog, cheese, shaving cream

  38. COLLOIDAL DISPERSION - The dispersed phase do not settle out under the influence of gravity and cannot be filtered out with filter paper - Difficult to distinguish with the naked eye but scatters a beam of light (Tyndall effect)

  39. DIALYSIS - The passage of ions and small molecules through semipermeable membranes - The semipermeable membrane is known as the dialyzing membrane - The membrane holds back colloid particles and large molecules but allows solvent, hydrated ions, and small molecules to pass through - This technique is used to clean blood of people with kidney malfunction

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