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Solutions

Solutions. Acids, Bases, and Salts. Solutions. Solutions are made up of a solute and a solvent. The solute is homogeneously (evenly) dispersed in another substance called a solvent. Example: Solution: lemonade Solute: powder and sugar Solvent: Water. Sugar Dissolved in Water.

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Solutions

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  1. Solutions Acids, Bases, and Salts

  2. Solutions • Solutions are made up of a solute and a solvent. • The solute is homogeneously (evenly) dispersed in another substance called a solvent. • Example: Solution: lemonade Solute: powder and sugar Solvent: Water

  3. Sugar Dissolved in Water When the sugar (sucrose) dissolves, the molecules align with the poles of the polar water molecules.

  4. Solutes and Solvents • To tell which is a solute and solvent: • Solutes are generally in smaller quantities. • Water is the most common solvent (although in a few examples it could be the solute)

  5. A solution is made up of .20L of oxygen gas and 0.80L of nitrogen gas. Which is the solvent? • The oxygen • The nitrogen • Neither because they are both gases

  6. A metal alloy solution is made up of 0.8g silver and 0.1g of nickel. Which is the solute? • The silver • The nickel • Neither because they are both solids

  7. How do solutions form? • Solutions form between solutes and solvents because of attractive forces between the molecules. • General rule: “Like dissolves like”, which means that ionic compounds dissolve (are miscible) in other ionic (or polar) compounds. Also, covalent compounds which are nonpolar are miscible.

  8. Like Dissolves Like (Miscibility)

  9. Immiscible Liquids

  10. Solubility vs. Miscibility Soluble Miscible Two substances can be uniformly mixed in any relative quantity (no definite solute or solvent) Ex. Methanol and water are miscible (can mix in any relative quantity) • One substance in lesser quantity (solute) is dissolved in the solution in greater quantity (solvent) • Ex. Sugar is soluble in water (water is not soluble in sugar)

  11. Electrolytes • Anelectrolyteis a substance that dissociates when dissolved in water. (Nonelectrolytes do not dissociate.) • These compounds conduct electricity based on this dissociation. • To dissociate means to separate into ions in solution. • Acids, bases, and salts (ionic compounds) are all electrolytes.

  12. Strong vs. Weak Electrolytes • Strong electrolytes fully dissociate in water. (ex. Ionic compounds, strong acids, strong bases) • Weak electrolytes only partly dissociate in water. (ex. Weak acids and weak bases) • Nonelectrolytes do not dissociate in water. (nonpolar covalent compounds)

  13. Classify the following substance: KBr • Strong electrolyte • Weak electrolyte • Nonelectrolye

  14. Classify the following substance: Acetic Acid (vinegar) • Strong electrolyte • Weak electrolyte • Nonelectrolye

  15. Classify the following substance: BH3 • Strong electrolyte • Weak electrolyte • Nonelectrolye

  16. Classify the following substance: HCl (hydrochloric acid) • Strong electrolyte • Weak electrolyte • Nonelectrolye

  17. Write an equation for the dissociation of magnesium nitrate in water.

  18. Write an equation for the dissociation of the weak acid, HF, in water.

  19. Saturated Solutions • When a solvent contains the maximum amount of solute, it is a saturated solution. • Therefore, if you add any more solute, it will not dissolve. • If you can still dissolve more solute, the solution is unsaturated.

  20. Effect of Temperature on Solubility • For most solids, solubility increases with temperature. • Temperature and solubility are therefore directly proportional. • At higher temperature, the molecules move faster and can therefore dissolve more solute.

  21. Supersaturated Solutions • Supersaturated Solutions – dissolve more than the accepted value of solute by heating the solution. When the solution cools, the solute will stay dissolved and the solution will be supersaturated.

  22. You add a given amount of sugar to a solution and all of it dissolves. Describe the solution. • Unsaturated • Saturated • Supersaturated • Unable to be determined

  23. You add a given amount of sugar to a solution and some it is left at the bottom of the beaker. The solution is: • Unsaturated • Saturated • Supersaturated • Unable to be determined

  24. You add a given amount of sugar to a solution and some it is left at the bottom of the beaker. You heat the solution and the rest dissolves. The solution is: • Unsaturated • Saturated • Supersaturated • Unable to be determined

  25. Beaker A has 2 g of solute dissolved while Beaker B has 1 g of solute dissolved. Which solution is more concentrated? • Beaker A • Beaker B • Unable to be determined

  26. Concentration • Concentration describes the amount of solute dissolved in a solution per unit solvent. • Molarity – most common concentration measurement in chemistry • Others used: Molality, normality, percent composition, ppm (parts per million), ppb (parts per billion)

  27. Molarity • Molarity (M) - ratio of the moles of solute per L of solution

  28. Molarity as a Conversion Factor

  29. Dilutions • Dilutions – used by adding solvent to make a less concentrated (more dilute) solution. • Dilution Equation: M1 V1 = M2 V2 • M = Molarity • V = Volume

  30. Volume (mL) Volume (L) of gas at STP 1000mL = 1 L Volume (L) 22.4L = 1 mol Molarity Molar Mass 6.02 x 1023 Atoms or Molecules Mass (g) Moles of A Mole Ratio Molar Mass 6.02 x 1023 Atoms or Molecules Mass (g) Moles of B Molarity 22.4L = 1 mol Volume (L) 1000mL = 1 L Volume (L) of gas at STP Volume (mL)

  31. Acids, Bases, and Salts

  32. Acids and Bases Acids, bases, and salts make up compounds known as electrolytes. Arrhenius acids – substances that ionize in water to produce the hydrogen ion, H+. Arrhenius bases – substances that ionize in water to produce the hydroxide ion, OH-.

  33. HCl(g) → H+(aq) + Cl-(aq) NaOH(cr) → Na+(aq) + OH-(aq) Dissociation – already formed ions separate Ionization – neutral molecules react with water to form charged ions

  34. Bronsted-Lowry Theory Bronsted acid – proton donor Bronsted base – proton acceptor HCl(g) + H2O(l) → H3O+(aq) + Cl-(aq) Conjugate base – particle that remains after a proton has been released by the acid Conjugate acid – particle that remains after a proton has been accepted by the base

  35. Conjugate Acids and Bases • The strength of conjugate acids and bases are inversely proportional.

  36. Conjugate pairs Every acid or base has a conjugate pair. Acid + base → conjugate base + conjugate acid

  37. HCl(g) + H2O(l) → H3O+(aq) + Cl-(aq) • In the reactants, which acts as the acid (proton donor) and which acts as the base (proton acceptor)? • What is the conjugate acid of the base? • What is the conjugate base of the acid?

  38. Strength of Acids and Bases Strength of acids and bases depends on how completely they ionize in water - the strongest acids and bases fully ionize in water while weak acids and bases only ionize slightly

  39. Strong acids (Know these)– HCl, HBr, HI are all strong, while all other binary acids are weak As a rule, all acids with at least two more oxygens than hydrogens are strong (H2SO4, HNO3,HClO4) Strong bases – Hydroxides of the Groups I and II elements except for Be are all strong.

  40. Kw • Kw for water is based on the equation: • 2H2O (l) -> OH- (aq) + H3O+ (aq) • Kw= [OH-][H3O+] = 10-14 • Therefore, if you know either hydroxide or hydronium concentrations, you can solve for the other.

  41. pH scale pH is the measure of the concentration of hydronium ion in a water solution pH = -log[H30+] Scale goes from 0 to 14. 0 to 7 is acidic, 7 is neutral, 7 to 14 is basic

  42. pH – log based • Every increase of 1 on the pH scale changes the concentration by a power of 10. • How much stronger is a substance with a pH of 4 vs a pH of 6?

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