SOLUTION AND SOLUBILITIES 2

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Component present in greater proportion is called the solvent, the one in minor proportion is called the solute Oceans are salt water solutions—water is the solvent, salt is the solute. Sweet tea in another example — sugar is the solute and water is the solvent Solute and solvent

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What is Happening?

How Substances Dissolve

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How It Happens

Student, Beware! Just because a substance disappears when it comes in contact with a solvent, it doesn’t mean the substance dissolved. Dissolution is a physical change—you can get back the original solute by evaporating the solvent. If you can’t, the substance didn’t dissolve, it reacted.

Copyright © Houghton Mifflin Company.All rights reserved. Presentation of Lecture Outlines, 12–19

John A. Schreifels Chemistry 212 Chapter Fig Solubility Equilibrium

Types of Solutions

Gaseous Solutions

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Dissolving Liquids and Gases

Solid Solutions

Dissolving Solids in Solids

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Factors Effecting Solubility

Solute-Solvent Interaction The number of -OH groups within a molecule increases solubility in water. Generalization: “like dissolves like”. The more polar bonds in the molecule, the better it dissolves in a polar solvent. The less polar the molecule the less it dissolves in a polar solvent and the better is dissolves in a non-polar solvent. The greater the contact between the solute and solvent, the faster the substance will dissolve. Therefore, stirring and crushing, which increases the surface area, increase the rate of solution Factors Affecting Solubility

Temperature Temperature will affect solubility. If the solution process absorbs energy then the solubility will be INCREASED as the temperature is increased. If the solution process releases energy then the solubility will DECREASE with increasing temperature. Factors Affecting Solubility

Temperature

Temperature Effects Experience tells us that sugar dissolves better in warm water than cold. As temperature increases, solubility of solids generally increases. Sometimes, solubility decreases as temperature increases (e.g. Ce 2 (SO 4 ) 3 ). Experience tells us that carbonated beverages go flat as they get warm. Therefore, gases get less soluble as temperature increases. Thermal pollution: if lakes get too warm, CO 2 and O 2 become less soluble and are not available for plants or animals. For solid solutes, as temp ↑, solubility ↑. For gas solutes, just the opposite. Factors Affecting Solubility

Pressure Effects The higher the pressure, the more molecules of gas are close to the solvent and the greater the chance of a gas molecule striking the surface and entering the solution. –Therefore, the higher the pressure, the greater the solubility. –The lower the pressure, the fewer molecules of gas are close to the solvent and the lower the solubility. Factors Affecting Solubility

Pressure Effects Carbonated beverages are bottled with a partial pressure of CO 2 > 1 atm. As the bottle is opened, the partial pressure of CO 2 decreases and the solubility of CO 2 decreases. Therefore, bubbles of CO 2 escape from solution. Factors Affecting Solubility

Pressure Effects Factors Affecting Solubility

Copyright © Houghton Mifflin Company.All rights reserved. Presentation of Lecture Outlines, 12–39 –Expressed mathematically, the law is where S is the solubility of the gas, k H is the Henry’s law constant characteristic of the solution, and P is the partial pressure of the gas.

SOLUTION AND SOLUBILITIES 41 SOLUBILITY GRAPH OF GASES IN WATER Pressure has little effect on the solubility of liquids and solids. The solubility of gases is strongly influenced by pressure. Gases dissolve more at high pressure.

Stirring

Surface Area

Controlling the Process

47 Identify the solute in each of the following solutions: A. 2 g sugar (1) and 100 mL water (2) B mL of ethyl alcohol (1) and 30.0 mL of methyl alcohol (2) C mL water (1) and 1.50 g NaCl (2) D. Air: 200 mL O 2 (1) and 800 mL N 2 (2)

48 Identify the solute in each of the following solutions: A. sugar (1) B. methyl alcohol (2) C. NaCl (2) D. O 2 (1)

Stir, and stir, and stir Add sugar to warm tea then add ice Grind the sugar to a powder Fresh solvent contact and interaction with solute Greater surface area, more solute- solvent interaction Faster rate of dissolution at higher temperature

Solution Concentrations

Dilute Small amount of solute for given solvent Concentrated Large amount of solute for given solvent Saturated Maximum amount of solute for given solvent But these terms are qualitative, not quantitative, and are open to interpretation.

Concentration

Copyright © Houghton Mifflin Company.All rights reserved. Presentation of Lecture Outlines, 12–55 Ways of Expressing Concentration Concentration expressions are a ratio of the amount of solute to the amount of solvent or solution. –The quantity of solute, solvent, or solution can be expressed in volumes or in molar or mass amounts. –Thus, there are several ways to express the concentration of a solution.

Copyright © Houghton Mifflin Company.All rights reserved. Presentation of Lecture Outlines, 12–56 Molarity The molarity of a solution is the moles of solute in a liter of solution. –For example, 0.20 mol of ethylene glycol dissolved in enough water to give 2.0 L of solution has a molarity of

Copyright © Houghton Mifflin Company.All rights reserved. Presentation of Lecture Outlines, 12–57 Mass Percentage of Solute The mass percentage of solute is defined as: –For example, a 3.5% sodium chloride solution contains 3.5 grams NaCl in grams of solution.

Copyright © Houghton Mifflin Company.All rights reserved. Presentation of Lecture Outlines, 12–58 Molality The molality of a solution is the moles of solute per kilogram of solvent. –For example, 0.20 mol of ethylene glycol dissolved in 2.0 x 10 3 g (= 2.0 kg) of water has a molality of

Solubility

SOLUTION AND SOLUBILITIES 60 The amount of solute per unit solvent required to form a saturated solution is called the solute's Solubility. When two liquids are completely soluble in each other they are said to be Miscible. Solubility is affected by Temperature. With increase in temperature solubility of most of the substances increases. Most gases become less soluble in water as the temperature increases.

SOLUTION AND SOLUBILITIES 61

Copyright © Houghton Mifflin Company.All rights reserved. Presentation of Lecture Outlines, 12–62 Factors in Explaining Solubility In most cases, “like dissolves like.” –This means that polar solvents dissolve polar (or ionic) solutes and nonpolar solvents dissolve nonpolar solutes. –The relative force of attraction of the solute for the solvent is a major factor in their solubility.

Copyright © Houghton Mifflin Company.All rights reserved. Presentation of Lecture Outlines, 12–63 Solubility and the Solution Process The amount of a substance that will dissolve in a solvent is referred to as its solubility. –Many factors affect solubility, such as temperature and, in some cases, pressure. –There is a limit as to how much of a given solute will dissolve at a given temperature. –A saturated solution is one holding as much solute as is allowed at a stated temperature.

the amount of solute dissolved in a solvent at a given temperature described as dilute or unsaturated if it has a low concentration of solute described as saturated if it has a high concentration of solute described as supersaturated if contains more dissolved solute than normally possible

Types of Solutions Saturated  Solvent holds as much solute as is possible at that temperature.  Dissolved solute is in dynamic equilibrium with solid solute particles.

Types of Solutions Unsaturated  Less than the maximum amount of solute for that temperature is dissolved in the solvent.

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Copyright © Houghton Mifflin Company.All rights reserved. Presentation of Lecture Outlines, 12–74 Heat can be released or absorbed when an ionic compound dissolves in water. –This heat of solution can be quite noticeable. –When NaOH dissolves in water, it gets very warm (the solution process is exothermic). –On the other hand, when ammonium nitrate dissolves in water, it becomes very cold (the solution process is endothermic).

1. Which substance’s solubility increases the most with temperature? 2. Which substance’s solubility changes the least with temperature? 3. What is the solubility of KI at 8 o C? 4. What temperature is needed to dissolve 160 g of potassium iodide, KI, in 100 g of water?

Solute (salt) Solvent (water) A Salt Water Solution

solute solvent solute solvent What is the Solute and what is the solvent? Label Each. 1.Cigarette Smoke and Air 2.Caffeine and Water (Cup of Coffee) 3.Water and Oxygen (Water in a Fish Tank) 4.Carbon Dioxide and Sugar Water (Sealed Can of Pop) 5.Oxygen and Nitrogen (Air) 6.Minerals and Water (Hard Water) 7.Water and Sugar (Maple Syrup) 8.Acetic Acid and Water (Vinegar) 9.Salt and Water (Ocean Water)

Solutions and mechanical mixtures can be separated in many ways Evaporation: the liquid evaporates and a solid(residue) is left behind Distillation: a 2 step process that: a)Heats a solution to change one part into gas and then, b)Cools the gas/vapor to liquid form and collects it

Separating Mixtures & Solutions Filtration: the use of a funnel and a filter paper to separate a solid from a liquid. The liquid passes through the filter paper and is called filtrate. The solid remains in the filter paper and is called residue Sifting: using a sieve, different sized substances can be separated Magnetism: a magnet can be used to remove metal from non- metallic substances

Separating Mixtures & Solutions After each of these observations, determine what is describes as either a pure substance or a mixture. Tap water leaves behind a white substance when it evaporates. When wet sand is filtered, the sand stays in the filter paper and the water goes through Distilled water leaves nothing behind when it evaporates.