Unit 9 -- Solutions Lundquist -- 2016

Unit 9.1 Solutions and Solubility Curves

Solutions Mixture of substances (2+) State of matter depends on the solvent Solute: substance that is dissolved Solvent: substance that does the dissolving

9.1 Note Quiz Questions 1. 2.

All about attraction!

Properties of solutions Homogeneous Cannot be filtered Transparent Can be separated by evaporating the solvent

9.1 Note Quiz Questions 3.

Solubility Soluble – if a substance can be dissolved in the solvent AKA: Miscible Insoluble – if a substance can not be dissolved in the solvent (< 1% ) AKA immiscible Solubility -- How much solvent can be dissolved in a solute at a given temp and pressure

Like Dissolves Like! Polar compounds dissolve polar compounds Water is the universal solvent because of its polarity Non-polar compounds dissolve non-polar compounds Benzene can dissolve plastic because both are non-polar

Solvation

9.1 Note Quiz Questions 4. 5.

Rate of solubility Since solubility occurs when molecules collide, increasing the rate of collisions will increase how much quickly the solute dissolves Stirring Increasing solute surface area Increasing temperature Since the molecules of solvent have to move between the molecules of solute energy is absorbed (endothermic process)

Factors that effect solubility Temperature Effects solid solubility mainly Direct relationship with solubility Pressure Effects gaseous solubility mainly Solubility increases as pressure around the solute increases Soda is bottled at a higher pressure, when opened it begins to effuse out.

Solubility curves Graph assumes a 100g sample of water, if you had 200g just double the values Different phases dissolve differently Solids Higher solubility at higher temp. (+) slopes Gases Higher solubility at lower temps (-) slopes

Solubility curves -think of it like a party Saturated – on the line “We’re out of seats, no one can come in till someone leaves.” Unsaturated – below the line Coach L’s usual party itinerary “We got room come on it!” To calculate how much more can fit in find out how much under the line you are on the Y-axis Supersaturated – above the line “I’ve hired a bouncer!” Excess is precipitate Solid falls out of solution To calculate: find how much you are over on the Y-axis and subtract till you get to the line

p. 14 KNO3 at 70oC NaCl at 100oC NH4Cl at 90oC In 50mL H2O NaCl at 100oC In 200mL H2O NH4Cl at 90oC Which is most soluble at 15oC?

p. 14 70g NaNO3 at 30oC 50g NH4Cl at 50oC 3. What is the solubility of KCl at 5oC

Do p. 13 -15 use note p. 4

9.1 Note Quiz 6. 7.

9.1 Note Quiz Questions 9. 8.

9.1 Note Quiz 10.

Unit 9.2 Units of Concentration Dilutions

𝑀= 𝑚𝑜 𝑙 𝑠𝑜𝑙𝑢𝑡𝑒 𝐿 𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛 Molarity Concentration – how much stuff do you have in a set space Molarity -- Concentration of molecules in a solution You are usually given grams so you have to convert You are usually given milliliters so you have to convert 𝑀= 𝑚𝑜 𝑙 𝑠𝑜𝑙𝑢𝑡𝑒 𝐿 𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛

Practice What is the molarity of a solution of 100mL of water and 36g of hydrochloric acid How many grams of sugar (C12H22O11) are in 500mL of a 0.5M solution?

9.2 Note Quiz Questions 1. 2. 3.

9.2 Note Quiz Questions 4. 5.

9.2 Note Quiz Questions 6. 7.

Making solutions

Do p. 8-10 SKIP #6 & #8 on p. 10

Other Units of concentration Molarity (M) Molality (m) 𝑀= 𝑚𝑜 𝑙 𝑠𝑜𝑙𝑢𝑡𝑒 𝐿 𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛 Volume can change with temperature (Charles Law) Not good for solutions that fluctuate in temp. 𝑚= 𝑚𝑜 𝑙 𝑠𝑜𝑙𝑢𝑡𝑒 𝐾 𝑔 𝑠𝑜𝑙𝑣𝑒𝑛𝑡 Not dependent on temperature since MASS never changes Good for temperature changes What is the molality of a solution made from 100.mL water and 5.0g NaCl?

Other Units of concentration Mole Fraction (c) Percent by Mass (%) 𝜒= 𝑚𝑜 𝑙 𝑠𝑜𝑙𝑢𝑡𝑒 𝑚𝑜 𝑙 𝑠𝑜𝑙𝑢𝑡𝑒 +𝑚𝑜 𝑙 𝑠𝑜𝑙𝑣𝑒𝑛𝑡 Same thing we used in Dalton’s Law Based off number of moles What is the concentration of a solution made from 0.4 mol benzene in 1.6mol naphaline? %= 𝑚𝑎𝑠 𝑠 𝑠𝑜𝑙𝑢𝑡𝑒 𝑚𝑎𝑠 𝑠 𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛 ×100 MOST COMMON in the real world What mass of sugar is in 25og of 10% sugar water?

Other Units of concentration Parts per Million (ppm) 𝑝𝑝𝑚= 𝑚𝑎𝑠 𝑠 𝑠𝑜𝑙𝑢𝑡𝑒 𝑚𝑎𝑠 𝑠 𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛 × 10 6 Based off mass percent A solution is made of 20g salt and 100mL water, what is the ppm salt? The SOL only tests M, however I require you to know: M m % c

Dilutions Adding the solvent to lower the concentration of the solute. The amount of solute (mols) remains unchanged LOWERS concentration (M)

Dilutions 𝑚𝑜𝑙 𝐿 1 𝐿 1 = 𝑚𝑜𝑙 𝐿 2 𝐿 2 𝑀 1 𝑉 1 = 𝑀 2 𝑉 2 Since the number of Moles doesn’t change when we change the volume we can find the new concentration with the following formula 𝑚𝑜𝑙 𝐿 1 𝐿 1 = 𝑚𝑜𝑙 𝐿 2 𝐿 2 𝑀 1 𝑉 1 = 𝑀 2 𝑉 2

Performing Dilutions

Practice What volume of a 3.0M KI solution would you use to make 0.300L of a 1.25M KI solution? How many milliliters of a 5.0M H2SO4 stock solution would you need to prepare 100mL of a 0.25M H2SO4? How much water would you need to add to your 5.0M stock solution to produce 100mL of 0.25M H2SO4 If you dilute 20.0mL of a 3.5M solution to make 100mL of solution, what is the molarity of the dilute solution?

9.2 Note Quiz Questions 8. 9. 10.

Do p. 11 & 12

Unit 9.3 Colligative Properties Types of Solutions

Colligative Properties of solutions Physical properties of solutions that are effected by the number of particles in solutions but NOT by the identity of dissolved particles in solution. Ionic compounds have a greater effect on colligative properties then covalent compounds Dissociation factor(df) or Van’t Hoff Factor (i) How many ions does the compound form? For non-electrolytic compounds (covalent compounds) the df is always one (1). For ionic compound the df is the number of ions that form that compound. Effect: Vapor pressure Boiling point Freezing point

Vapor pressure number of solvent particles exposed to surface, less enter gas phase Lower vapor pressure

Boiling Point Increases because fewer particles on the surface are contributing to the vapor pressure (takes more energy to raise the vapor pressure) Dependent on vapor pressure Kb = difference in temp. of solution and pure solvent

Freezing point When kinetic energy can no longer overcome attraction Decreases because solute particles get in the way of attractive forces, cause the more energy to need to be lowered for phase change

Calculating the effect of solute on freezing points and boiling points Where DT = change in BP or FP (°C) m = molality ( 𝑔 𝑘𝑔 ) or concentration of solution i = dissociation factor K = constant for solvent (given) Boiling Point 𝛥𝑇=𝑚 𝐾 𝑏 𝑖 𝐵𝑃=𝐵 𝑃 ∘ +𝛥𝑇 Freezing Point 𝛥𝑇=𝑚 𝐾 𝑓 𝑖 𝐹𝑃=𝐹 𝑃 ∘ −𝛥𝑇

What is the freezing point of a 0 What is the freezing point of a 0.40m solution of sucrose in ethanol, if ethanol’s normal freezing point is -114.1°C? (Kf = 1.99 °C/M) DT = m(df)K m = 0.40m i = 1 K = 1.99 °C/m DT = 0.40M (1) 1.99°C/m DT = 0.796°C New freezing point = -114.1°C – 0.796°C = -114.896°C

Do p. 16-19

Types of Solutions Solutions Colloid Very small particles Light passes through it easy (transparent) Large particles Scatters light passing through it Will NOT settle

Types of Solutions Suspensions VERY large particles Will settle out over time

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