CHMY 143 Chapter 13 PDF

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Dr. Goodman's Lecture over Chapter 13 about Solutions from 2/15/20....

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CHMY 143 | January 15,2020 | Lecture 2 Energetics of Solution Formation - Endothermic v. exothermic reactions (how they form) Quantifying Solutions - Molarity, Mass Percent, Mole Fraction Reading Sections - 13.3-13.5 pgs. 544-557 - 31,35,37,41,45,47,49,51,55,57,61 Energy and Dissolution

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Positive is consuming energy (endothermic) Negative is releasing energy (exothermic) Can begin to make predictions on endothermic/exothermic

Like Dissolves Like - Referring polarity in molecules - Look and formula and structure

iClicker Question: - Which of the following liquids would you expect to be soluble in liquid hexane (C6H13)?

CHMY 143 | January 15,2020 | Lecture 2 a. b. c. d.

Propane (C3H8) - the formula is the most similar Hydrogen Chloride (HCl) Water (H2O) Ammonia (NH3)

Energetics of Making a Solution - Regardless of the phases of the solute and solvent, solubility will depend on the energy - The sign of �Hsoln (enthalpy of solution) will tell us if making our solution is an exothermic or endothermic process - Positive = system gained/absorbed energy = endothermic - Negative = system lost energy = exothermic (initial higher than final)

Energetics of Making a Solution - Can calculate �Hsoln from the lattice energy (�Hlattice, which reflects the energy of solutesolute interactions) and the heat of hydration (�Hhydration, which reflects the energy of both solute-solute and solvent-solute interactions)

Energetics of Solutions - Heat of hydration (�Hhydration) is the energy released or absorbed when a solute dissolves in H2O - Formal definition: energy change when 1 mol of gaseous ions

CHMY 143 | January 15,2020 | Lecture 2

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are dissolved in H2O Lattice Energy (�Hlattice) is the energy associated with the formation of a crystalline lattice of oppositely charged ions.

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iClicker

CHMY 143 | January 15,2020 | Lecture 2

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ANSWER: C

Effect of Temperature and Pressure on Solubility - As temperature increases, solubility of a solid generally increases - The solubility of a solid is not typically affected by pressure changes - For a gas, increasing temperature decreases solubility - And gas solubility increases with increasing pressure Henry’s Law - The solubility of a gas (Sgas) is directly proportional to its partial pressure, (Pgas) - Sgas = kHPgas - kH is called the Henry’s Law Constant

Announcements - HW 1 is open (Due Tuesday because of the Monday holiday)

CHMY 143 | January 15,2020 | Lecture 2 -

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Make sure you are going through D2L to register for Mastering Chemistry (you should not need a course ID) Don’t forget to register your iClickers (link available in D2L) 1st Exam is 2 ½ weeks from today (1/15)

Quantitative Side of Solutions - We can show the amount of solute dissolved in a solvent as the concentration - Concentration is the amount of solute dissolved per unit volume - Weak coffee has a lower concentration (dilute) and is fainter in color than strong coffee (concentrated) - Most often we use the units of moles of solute per liter of solution. This is called the molarity. - Molarity = moles of solute/liters of solution - Unit for molarity is M - ‘Liters of solution’ will change the temperature (which means molarity will change with temperature) - There are three things that are typically asked when working with solutions: - Find M if given mol (or gram) and V (in L) - Find V (in L) if given mol (or gram) and M - Find mol (or gram) if given M and V (in L) - Example: what is the molarity of a 2.0 L solution that contains 162 g Na3PO4?

Molality - What do we use to express concentration when temperature changes? - Need a unit that is unchanging with temperature - M = mol solute/kg solvent - Molality - Both mol solute and mass of solvent do not change with changing temperature - Oftentimes, molality is close to Molarity… but they are not the same Other ways to report concentration - Mole fraction - The moles of one compound relative to the total number of moles

CHMY 143 | January 15,2020 | Lecture 2

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% composition by mass - Similar to mole fraction but now mass based

- Sum of all masses must = 100% - 5% NaCl solution is common for contact lens solutions - Parts per million (ppm) - Equivalent to calculating mg/kg - Example: The highest recorded mercury concentration in tuna was 1.4 ppm. How many grams would be in an 11oz (1 oz. approx 28.35g) steak of this tuna?...