X Unit 14 Solutions & Acids and Bases

Transcription

1 1 X Unit 14 Solutions & Acids and Bases I. Solutions All solutions are composed of two parts: the and the. o Solute o Solvent A solution may exist as a solid, liquid, or gas depending on the state of the solvent. Examples: Type of Solution Example Solute Solvent Appears as: Gas in Liquid Liquid Solid in Solid Gas in Gas Liquid in Liquid Solid in Liquid Solid Gas Liquid Liquid o Aqueous Solution any solution where is the II. Solubility o Soluble o Insoluble

2 2 o Immiscible two liquids that are in each other o Miscible two liquids that are in each other o Solvation a process that occurs when an ionic solute dissolves in a solvent Like Dissolves Like Like Dissolves Like Solvents of a specific polarity or type will dissolve solute of similar polarities or types! Examples: Solubility o Solubility the maximum amount of solute that will dissolve in a given quantity of solvent at a specific temperature and pressure to produce a saturated solution o Units for solubility = o Example: At 20 C, NaNO3 has a solubility of 74 g NaNO3 / 100 g of H2O Saturation o contains the maximum amount of dissolved solute o contains less than the maximum amount of dissolved solute o contains more solute than can theoretically be dissolved at a given temperature

3 3 III. Solubility Curves The solubility of a solid generally with increasing temperature. (The higher the temperature, the amount of solute that will be dissolved in the solvent). Example #1: a) What is the solubility of KClO3 at 70 C? b) At what temperature are the solubilities of CaCl2 and NaNO3 the same? c) How many grams of K2Cr2O7 would be needed to make 200 grams of a saturated solution at 30 C? d) Which compound is most soluble at 20 C? *** affects solubility. For a solid, the higher the temperature, the more solute will dissolve. For a gas, the opposite is true.

4 4 IV. Concentration o Concentration Concentration Description Formula massof solute Percent by mass percent bymass 100 massof solution volumeof solute Percent by volume percent byvolume 100 volumeof solution Molarity molesof solute Molarity(M) litersof solution Example #2: An aquarium contains 3.6 grams of NaCl per grams of water. What is the percent by mass of NaCl in the solution? Example #3: What is the percent by volume of ethanol in a solution that contains 35 ml of ethanol dissolved in 115 ml of water?

5 5 Molarity Molarity (M) = o Molarity = moles of solute dissolved in 1 liter of solution. Example: o M is read as when next to a number. 4 M HCl = Example #4: What is the molarity of a solution that contains 0.65 moles of CuCl2 in 500 ml of water? Example #5: What is the molarity of a solution that contains 5.10 grams of glucose (C6H12O6) in ml of solution?

6 6 Preparing Molar Solutions (How to make a solution with a specific molarity) 1. Convert moles of solute to grams and measure the amount out. 2. Add solvent so that the total volume of the solution is 1 L. 3. For any volume other than 1 L, we must adjust the amount of solute needed by multiplying it by the fraction of a liter of solution we need. Example #6: How many grams of CaCl2 would be dissolved in 1.0 L of water to make a 0.10 M solution of CaCl2? Example #7: How many grams of NaOH are in 250 ml of a 3.0 M NaOH solution? V. Dilutions Dilutions are used to of a solution.

7 7 Steps to Performing a Dilution 1. Calculate how many ml of the original (stock) solution to start with 2. Measure out the volume of stock solution (using a graduated cylinder or a pipet) and place in appropriately sized volumetric flask 3. Add water to the mark on flask Example #8: What volume, in milliliters, of 2.0 M CaCl2 is needed to make 0.50 L of M CaCl2 solution? Example #9: What volume of water would you add to ml of a 6.77 M solution of nitric acid (HNO3) in order to get a 1.50 M solution? VI. Colligative Properties Colligative means. o Depends only on the of dissolved particles, not on the of the dissolved particles. o Examples of colligative properties:

8 8 Electrolytes o Soluble ionic compounds o When they dissolve in solution, they dissociate completely into ions. o Conduct o Example: NaCl (aq) Boiling Point Elevation o Boiling occurs when equals o The boiling point of a is than the boiling point of the. o Dissolving substances increases the boiling point of a solvent. Freezing Point Depression o Freezing point of a is lower than the freezing point of the. o Dissolving substances lowers the freezing point of a solvent. o Example: ***Example: Antifreeze (ethylene glycol in water) prevents car s radiator from boiling over in the summer (raises boiling point of water) & prevents car s radiator from freezing in the winter (lowers freezing point of water) END OF PART CONTINUE TO PART 2 (Acids & Bases)

9 9 VII. Acids & Bases Properties of Acids o Physical Properties Taste sour o Chemical Properties o Litmus Indicator o Ions in Solution Turns litmus paper Properties of Bases o Physical Properties o Chemical Properties Taste bitter Slippery (like soap) o Litmus Indicator o Ions in Solution Turns litmus paper

10 10 Arrhenius Model of Acids & Bases ACIDS: BASES: Ex.) Ex.) Bronsted-Lowry Acids & Bases For every acid, there must be a base! ACID = BASE = HCl (aq) + NH3 (aq) NH4 + (aq) + Cl - (aq) Conjugate Pairs o Conjugate pair = Ex.) NH3/NH4 + is a conjugate pair o Every acid has a conjugate base, formed when H + is from the acid. o Every base has a conjugate acid, formed when H + is to the base.

11 11 Example #10: Identify the conjugate pair of each compound HCl in water NaOH in water NH3 in water Types of Acids Acids can contain 1 or more hydrogens that are acidic. (Not all hydrogens are acidic). Ex.) vinegar, CH3COOH Example: Identify the following acids as monoprotic (1 acidic hydrogen) or polyprotic (multiple acidic hydrogens) HNO3 H3PO4 HClO4 H2SO4 HC2H3O2 HClO Strengths of Acids Strong acids o 100% dissociation o Strong acids: o Everything else is a weak acid!! Weak Acids o Equilibrium occurs (molecules break apart and then recombine) o Not all H + ions separate ( )

12 12 Strengths of Bases Strong bases o 100% dissociation o Generally Group 1 & 2 hydroxides (Ex: ) o Everything else is a weak base!! Weak Bases o Equilibrium occurs (breaks apart and then recombines) o Not VIII. ph o ph tells the or of a solution o Based on measuring the [H + ] a.k.a. [H3O + ]

13 13 ph Equations: Example #12: What is the ph and poh for a solution with an H + concentration, [H + ], of 3.0 x 10-6 M? Example #13: What is the [H + ] and [OH - ] of blood with a ph of 7.40? IX. Neutralization Reactions o Neutralization reaction Acid + Base Water + Salt o any ionic compound formed as a result of an acid-base reaction

14 14 Acid-Base Titration o Titration = Lab technique which allows you to get moles of acid and base EXACTLY equal to another o Complete o Allows you to calculate the concentration of an unknown acid or base o Defintions: o the substance of known concentration used to determine the unknown concentration of the other substance. o substance that changes color at a certain ph is added to tell us when the neutralization is complete. Common indicator = phenolpthalein o ph at which amount of acid = amount of base o End point Point at which the volume of titrant added makes the amount of acid and base are equal and the indicator changes color