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. - 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 SOLUTION

4. - 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 (O 2, Ar, etc. in N 2 ), - NO x, SO 2, CO 2 in the atmosphere SOLUTION

5. - 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 o C is 204 g/100 mL H 2 O Three factors that affect solubility - Temperature - Pressure - Polarity SOLUBILITY

6. 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 SOLUBILITY

7. - 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) PROPERTIES OF SOLUTIONS

8. - A solution in which water (H 2 O) is the solvent NaCl solution: solvent is H 2 O 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 AQUEOUS SOLUTION

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

10. 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 AQUEOUS SOLUTION

11. Solvation Process - Ions in aqueous solution are surrounded by the H 2 O molecules - The O atom in each H 2 O 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) AQUEOUS SOLUTION

12. Molecular Compounds - Most molecular compounds do not form ions in aqueous solution - The molecules disperse throughout the solution - Molecules are surrounded by H 2 O 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) - HNO 3 dissociates into H + (aq) and NO 3 - (aq) AQUEOUS SOLUTION

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

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

15. - 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 CONCENTRATION OF SOLUTIONS

16. 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. CONCENTRATION OF SOLUTIONS

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

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

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

20. 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 CONCENTRATION OF SOLUTIONS

21. 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 CONCENTRATION OF SOLUTIONS

22. 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 CONCENTRATION OF SOLUTIONS

23. 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 CONCENTRATION OF SOLUTIONS

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

25. 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. CONCENTRATION OF SOLUTIONS

26. DILUTION Consider a stock solution of concentration M 1 and volume V 1 If water is added to dilute to a new concentration M 2 and volume V 2 moles before dilution = moles after dilution M 1 V 1 = M 2 V 2 Calculate the volume of 3.50 M HCl needed to prepare 500.0 mL of 0.100 M HCl (3.50 M)(V 1 ) = (0.100 M)(500.0 mL) V 1 = 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. NaOH + HCl → NaCl + H 2 O 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 CHEMICAL ANALYSIS

29. How many grams of KOH are needed to neutralize 25.00 mL of 0.250 M H 2 SO 4 solution - Write balanced equation and determine mole ratio - Calculate moles of H 2 SO 4 - Determine moles of KOH - Calculate grams of KOH using molar mass CHEMICAL ANALYSIS

30. 2KOH + H 2 SO 4 → K 2 SO 4 + 2H 2 O 2 mole KOH : 1 mole H 2 SO 4 mole H 2 SO 4 = 0.250 M x 0.02500 L = 0.00625 mol Mole KOH = 2 x 0.00625 mol = 0.0125 mol CHEMICAL ANALYSIS

31. - 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, NH 4 Cl, KBr, NaNO 3 Strong acids: HCl, HNO 3, H 2 SO 4 Strong Bases: NaOH, KOH, Ca(OH) 2 ELECTROLYTES

32. - 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 (HC 2 H 3 O 2 ), citric acid (C 6 H 8 O 7 ) Weak bases: ammonia (NH 3 ) methylamine, cocaine, morphine ELECTROLYTES

33. - Single arrow is used to represent ionization of strong electrolytes H 2 SO 4 (aq) → H + (aq) + HSO 4 - (aq) - Ions have no tendency of recombining to form H 2 SO 4 - Double arrow is used to represent ionization of weak electrolytes HC 2 H 3 O 2 (aq) ↔ H + (aq) + C 2 H 3 O 2 - (aq) - This implies reaction occurs in both directions - Chemical equilibrium is when there is a balance in both directions ELECTROLYTES

34. NONELECTROLYTES - Substances whose aqueous solutions do not contain ions Examples Many molecular compounds Sucrose (C 12 H 22 O 11 ) ethanol (C 2 H 5 OH)

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. 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 COLLIGATIVE PROPERTIES

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. - 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) COLLOIDAL DISPERSION

39. - 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 DIALYSIS