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Solutions Chapter 22 Sections 1 - 4 Solutions Section 1 How Solutions Form slides 3-14 Section 2 Solubility & Concentration slides 15-28 Section 3 Particles in Solution slides 29-38 Section 4 Dissolving Without Water slides 39-49 1 How Solutions Form What You’ll Learn: Three types of solutions How things dissolve The rate solids and gases dissolve What is a solution? A solution is a mixture that has the same ingredients, color, density, and even taste mixed evenly throughout. You can’t see the sugar crystals because they have broken up into molecules that mix with water molecules and food coloring. Solutes and Solvents The solute is the substance that dissolves. The solvent is the substance that is doing the dissolving. In sugar-water, sugar is the solute and water is the solvent. What can dissolve in a liquid? In a solution made with a liquid & a solid, the solid is the solute & the liquid is the solvent. Which is which in salt water? What can dissolve in a liquid? In a solution made with a liquid & a solid, the solid is the solute & the liquid is the solvent. Which is which in salt water? Some solutions are gas dissolved in a liquid like carbonated soda in which carbon dioxide is dissolved in water. What can dissolve in a liquid? In a solution made with a liquid & a solid, the solid is the solute & the liquid is the solvent. Which is which in salt water? Some solutions are gas dissolved in a liquid like carbonated soda in which carbon dioxide is dissolved in water. Other solutions have a liquid dissolved in another liquid like food coloring in water with the solvent being the one present in a larger amount. Are there solutions that do not contain a liquid? Solutions can be mixtures of gases or even mixtures of solids. Air 78% N, 20% O, etc of other gases Sterling silver is a mixture of silver & copper, a solid solution or alloy is melted together Brass is copper & tin How Substances Dissolve A solid starts to dissolve at its surface. Water molecules are always moving and they are polar. Polar means they have a positive end and a negative end. Sugar is also polar so that the positive ends of the sugar molecules attract the negative ends of the water molecules. The water pulls the sugar into solution removing layer after layer of sugar until the crystal is dissolved. How do liquid & gas solutions form? It is similar but more complex because liquids and gases move much faster than solid particles. The movement separates the solute particles and mixes them evenly in the solvent resulting in a homogeneous solution. How do solids dissolve in other solids? Solids must be melted into liquids & then mixed together. In the liquid state, atoms move more freely to spread and form a homogeneous solution which stays even after cooling. Rate of Dissolving: Can be increased by stirring or heating. Increases particle speed If the solute is a solid you can break it into smaller pieces. Increases surface area Can you combine these methods? o The rate of dissolving increases with each additional method you use. 2 Solubility & Concentration What You’ll Learn: What solubility is About the concentration of solutions Three types of solutions Factors that affect gas solutions How much can dissolve? Solubility is the greatest amount of solute that can dissolve in a specific amount of solvent at a given temperature. How much can dissolve? Solubility is the greatest amount of solute that can dissolve in a specific amount of solvent at a given temperature. The difference of solubilities of solutes depends on the nature of the solute and the nature of the solvent. How much solute is in a concentrated solution? Concentration may be stated as a percentage by volume of the solute. A drink with 10 percent fruit juice has 10 mL of juice in 100 mL of the drink. Types of Solutions You can use the amount of solute dissolved to describe 3 different types: Saturated Unsaturated supersaturated What is a saturated solution? A saturated solution is one that contains all the solute it can hold at a given temperature. If you increase the temp of the mixture, more solute can dissolve. As shown in the following table, the solubility of solid solutes increases as the temperature of the liquid solvent increases. Solubility of Compounds in g/100 g of Water compound 0°C 20°C 100°C Copper(II) sulfate 23.1 32.0 114 Potassium bromide 53.6 65.3 104 Potassium chloride 28.0 34.0 56.3 Potassium nitrate 13.9 31.6 245 Sodium chlorate 79.6 95.9 204 Sodium chloride 35.7 35.9 39.2 Sucrose (sugar) 179.2 203.9 487.2 What is a solubility curve? Each line on the graph is a solubility curve for a substance. To find how much of a substance dissolves at a particular temp, find the temp on the x-axis & trace the line upward to the curve for that substance. What is an unsaturated solution? An unsaturated solution can dissolve more solute at a given temperature. An unsaturated solution can have any amount of copper (II) sulfate less than 32 g in 100 g of water at 20°C. www.sunflowerlearning.com/images/di.gif How can a solution be supersaturated? Honey is naturally a supersaturated solution. A supersaturated solution has more solute than a saturated solution at the same temperature. These solutions are unstable & may crystallize w/ any addition of solute. When do solutions give off energy? Supersaturated sodium acetate solution becomes hot as sodium acetate crystallizes. Sometimes when bonds form, energy is given off in the form of heat. Some heat packs are filled with a supersaturated solution that gives off heat as the solute crystallizes. When do solutions give off energy? Some solutes take energy from their surroundings to dissolve. As a result, the temperature of the solution is reduced. Ammonium nitrate is an example. A cold pack has inner bags of water & ammonium nitrate. A solution forms when the inner bags are broken; energy is drawn from the water as the solution forms causing the temperature to drop thus the pack feels cool. Solubility of Gases Soda is a solution of carbon dioxide gas dissolved in flavored water. When you shake an open bottle of soda, it bubbles. Shaking or stirring a solution of a gas in a liquid allows more gas molecules to reach the surface of the liquid, where they escape into the air. How do pressure & temperature affect a gas dissolved in a liquid? Soda is bottled under a great amount of pressure to force more gas to dissolve in the soda & to keep the gas in solution. When you open the can, the pressure is released & bubbles of gas come out of solution. Cooling a liquid increases the amount of gas that will dissolve in it (opposite of solids). Warm soda bubbles more than cold. 3 Particles in Solution What You’ll Learn: How some solutes form positively or negatively charged particles How some solutions conduct electricity How antifreeze works Particles with a Charge A particle with a charge is an ion. Ions are throughout your body in fluids helping nerve cells send messages controlling your muscles. An electrolyte is a compound that produces solutions of ions that conduct electricity in water. Strong electrolytes, like NaCl dissolve completely into ions, conduct a strong electric current. Particles with a Charge Weak electrolytes, like acetic acid in vinegar, stay mainly as molecules when they dissolve in water, produce only a few ions and conduct current weakly. Nonelectrolytes are substances that do not form ions in water and cannot conduct electricity. Organic molecules like sucrose (sugar) and ethyl alcohol are examples. How do ionic solutions form? Ionization, the process of forming ions, happens when molecules are broken apart so that the atoms take on a charge. Polar molecules divide into ions, ex. HCl & waterH3O+ (hydrogen ion in water) The separation of ionic compounds into positive and negative ions is called dissociation. The next slide shows what happens to NaCl as it dissociates with H drawn to Cl & Na to O due to opposite charges. Sodium & Chloride Ions Mixed w/ Water Effects of Solute Particles All solute particles can affect physical properties of a solvent, such as freezing point & its boiling point. How does antifreeze lower the freezing point? As a substance freezes, its particles arrange themselves in an orderly pattern. Solute particles interfere with this pattern making it harder for the solvent to freeze. A lower temperature is needed to freeze the solvent. Why can some animals live in a cold climate? Caribou have substances in their bodies that keep their legs from freezing. Fish also have a natural kind of antifreeze that keeps ice crystals from forming in their tissues. Many insects have a similar chemical to protect them. How can the boiling point of water be raised? Antifreeze also raises the boiling point of water by interfering with the evaporation of solvent particles. More energy is needed for the solvent particles to escape from the liquid surfaces. The more solute particles in the solution, the higher the boiling point of the solution will be. How does antifreeze work in a car radiator? Solute particles block part of the surface so fewer water molecules can reach the surface & vaporize. The solution cannot boil because the vapor pressure of the solution is lower than the vapor pressure of the solvent. Added energy is required to raise the vapor pressure & make it boil. 4 Dissolving Without Water What You’ll Learn: What solutes do not dissolve in water How polar and nonpolar solvents work in water How to choose the right solvent for cleaning When Water Won’t Work There are some things, such as salad dressing with vinegar and oil, that water cannot dissolve. Water molecules dissolve polar solutes but not most nonpolar ones without positive & negative areas. How do nonpolar solutes behave? Salad oils are made of large hydrocarbon molecules which share electrons in a nearly equal way. These nonpolar oil molecules are not attracted to polar water molecules. This is also why you have to shake oil and vinegar dressing to mix it before using it. Why are alcohols special? Molecules of some substances have a polar end and a nonpolar end so they can form solutions with polar and nonpolar solutes. This is ethanol with an OH group that’s polar & the rest which It can dissolve both nonpolar iodine is nonpolar. and polar water. Useful Nonpolar Molecules Mineral oil can be used to remove candle wax from candleholders, bubble gum from some surfaces. To remove wet paint or make it thinner use turpentine. Gasoline is a solution of different hydrocarbons. Dry cleaners use nonpolar solvents. Remember “like dissolves like”. When are nonpolar solvents not helpful? Many nonpolar solvents are flammable or burn easily. Some are toxic & should never be used in a closed room. They evaporate readily so you must always have fresh air when using them. How does soap work? Natural oils on your skin and hair keep them from drying out, but they also attract and hold dirt in a nonpolar mixture. You need to use soap with both polar and nonpolar properties to wash it away. How does soap work? Soaps start out as large fatty acid molecules with long hydrocarbon ends that are nonpolar. A carboxylic acid group, COOH, is at the other end. Without the H atom, the end has a negative charge. How does soap work? The ionic end of a soap molecule dissolves in water. The nonpolar end dissolves in oily dirt. Together the two ends of a soap molecule remove dirt so it can be rinsed away. Polarity & Vitamins Vitamin A from liver, lettuce, cheese, eggs, carrots, sweet potatoes, and milk can dissolve in body fat because both are nonpolar. Fat-soluble vitamins can be very harmful at high concentrations. Polar vitamins, such as B & C dissolve in the water in your body. Excess vitamins wash away. Eat a healthful diet to avoid harmful overdose.
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