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Chapter 8

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For a solution to form, one substance must dissolve in another. Even though we usually think of a solid dissolving in a liquid, any state of matter can become part of a solution. Scuba divers breathe with the aide of compressed air(78% nitrogen). As a diver descends (the deeper the diver goes), the greater is the pressure of the air in the divers lungs and the more nitrogen dissolves in the blood and tissues of the body. If divers surface too quickly, the nitrogen that has dissolved in the blood and tissues can bubble out of the solution and become trapped in joints causing great pain (the bends).

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A solution is a homogeneous mixture of two or more substances. Every solution has two types of components: a solute (salt) and a solvent(water). For a solute to dissolve in water, the solute and solvent particles must attract one another. Solutes and solvents can be solids, liquids or gases.

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Substances can dissolve in water three ways: Dissociation of Ionic Compounds: sodium chloride crystal and water Dispersion of Molecular Compounds: hard candy and saliva Ionization of Molecular Compounds: HCl and water The process in which neutral molecules gain or lose electrons is known as ionization.

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Three physical properties of a solution that can differ from those of its solute and solvent are as follows: Conductivity Sodium chloride dissociates in water Hydrogen chloride ionizes in water Freezing point Magnesium chloride dissociates and interferes with the freezing process changing it from 0 C to as low as -15C Boiling point Ethylene glycol and water (coolant in most car radiators) raises the boiling point of water from 100 C to prevent overheating

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During the formation of a solution, energy is either released or absorbed. Sodium hydroxide dissolves in water and becomes warmer (exothermic: releasing energy to the surroundings) Ammonium nitrate, used in cold packs, dissolves in water and becomes colder (endothermic: absorbing energy from the surroundings) In order for a solution to form, both the attractions among solute particles and the attractions among solvent particles must be broken. Breaking of attractions requires energy. As the solute dissolves, new attractions form and the formation of attractions releases energy. The is the difference between these energies.

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Factors that affect the rate of dissolving include surface area, stirring and temperature. The more frequent the collisions between the solute and solvent, the faster rate of dissolving.

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Lemonade, Iced tea, and hot tea can all hold different concentrations of sugar. They each have different factors for solubility of sugar.

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The maximum amount of a solute that dissolves in a given amount of solvent at a constant temperature is called solubility. Grams of solute per 100 grams of solvent at a specified temperature Knowing the solubility of a substance can help you classify solutions based on how much solute they contain. Solutions are described as saturated(solvent filled with solute), unsaturated(solvent does not fill the solute) or supersaturated(more solute than the solution can hold), depending on the amount of solute in solution at a given temperature.

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Three factors affect the solubility of a solute. Polar and Nonpolar Solvents oil is soluble in soapy water -like dissolves like Temperature generally, solubility increases as the temperature increases (iced tea versus hot tea with sugar) Pressure 12-ounce can of soda/carbonation (CO2) dissolved in a liquid

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Concentration can be expressed as percent in three ways. Percent by Volume Percent by Mass Molarity

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Sodium hydroxide (a base) is added to a mixture of animal/vegetable fats and boiled until the sodium hydroxide reacts with the fats producing glycerol and soap. After glycerol is separated from the soap, the soap is purified and other chemicals are mixed in for color and scent.

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An acid is a compound that produces hydronium ions when dissolved in water. Some general properties of acids include sour taste, reactivity with metals, and ability to produce color changes in indicators. Sour Taste: lemons, grapefruits, limes, and oranges (citric acid) vinegar (acetic acid) Reactivity With Metals: aluminum foil over spaghetti sauce (citric acid) a single replacement reaction Color Changes in Indicators: litmus paper (a common indicator) turns red in the presence of an acid

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A base is a compound that produces hydroxide ions when dissolved in water. Some general properties of bases include bitter taste, slippery feel, and ability to produce color changes in indicators. Bitter Taste: unsweetened chocolate, many cough syrups Slippery Feel: wet soap, some wet rocks Color Changes in Indicators: bases turn litmus paper blue

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Phenolphthalein: In a basic solution, is red In an acidic solution, is colorless Natural indicators: flowers, like hydrangeas In basic soil, flowers are pink In acidic soil, flowers are blue

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The reaction between an acid and a base is called neutralization. FISH BASE LEMON ACID REACTION MAKES FISH TASTE LESS BITTER This reaction is called neutralization. The neutralization reaction between an acid and a base produces a salt and water.

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Certain compounds of chlorine are dissolved in swimming pool water to prevent the growth of bacteria. The concentration of hydronium ions in solutions must be carefully controlled. Determining the concentration of hydronium or hydroxide ions is one way to determine the acidity or basicity of a solution.

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Chemists use a number scale from 0 to 14 to describe the concentration of hydronium ions in a solution. The PH of a solution is a measure of its hydronium ion concentration. 7 is neutral Acids have a pH less than 7 Bases have a pH greater than 7 The lower the pH value, the greater the H3O+ ion concentration in solution is. The higher the pH value, the lower the H3O+.

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To review Some reactions go to completion while other reach equilibrium When certain acids and bases dissolve in water, the formation of ions from the solute almost goes to completion. These acids and bases are classified as strong. Strong Acids When strong acid dissolve in water, they ionize almost completely. Examples: sulfuric acid and nitric acid Strong Bases Strong bases dissociate almost completely in water. Examples: calcium hydroxide and potassium hydroxide

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Weak acids and bases ionize or dissociate only slightly in water. Weak Acids Citric acid in orange juice, acetic acid in vinegar Equilibrium favors the reactants over the products so few ions form in solution Have a higher pH Weak Bases Toothpaste and shampoo contain weak bases Ammonia (colorless gas with distinctive smell) Buffers A solution that is resistant to large change in pH Prepared by mixing a weak acid and its salt or a weak bases and its salt pH is relatively constant

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Sports drinks taste salty because they contain salts of elements; they help restore the balance of ions in your body. Electrolytes ionize or dissociate into ions when they dissolve in water and results in a solution that can conduct an electric current. Strong acids and bases are strong electrolytes because they dissociate or ionize almost completely in water. Batteries and fuel cells also produce electricity and contain electrolytes.

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Class Participation Opportunity: Write a research paper that includes the following concepts: 1. compounds in blood 2. blood flow through the body 3. maintaining bloods pH 4. scientists who have contributed to our understanding of blood Your paper should include information found on pages 250-253. It should also contain information from two other sources.

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Possible investigative questions: Determining Solubility 1. How can you determine the solubility of a substance in water? Comparing Solubilities and Rates of Dissolving 2. How does surface area affect the rate of dissolving and solubility? 3. How does temperature affect the rate of dissolving and solubility? Testing Antacids 4. Which antacid neutralizes stomach acid with the smallest number of drops? Comparing Antacids 5. Which brand of antacid neutralizes the most acid per dose?