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Chapter 8

Chapter 8 . Solutions, Acids, and Bases. 8.1 Formation of Solutions. Dissolving. Recall that a solution is a homogeneous mixture of two or more substances Every solution has two components: Solute Substance whose particles are dissolved in a solution Solvent

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Chapter 8

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  1. Chapter 8 Solutions, Acids, and Bases

  2. 8.1 Formation of Solutions

  3. Dissolving • Recall that a solution is a homogeneous mixture of two or more substances • Every solution has two components: • Solute • Substance whose particles are dissolved in a solution • Solvent • Substance in which the solute dissolves • Ex. Seawater – water is solvent, salt is solute

  4. Dissolving • Solutes and solvents can take the form of solid, liquid, or gas • Solution takes state of solvent • Substances can dissolve in water in three ways • Dissociation • Dispersion • Ionization

  5. Dissociation of Ionic Compounds • For a solute to dissolve in water • The solute and solvent particles must attract to one another • The solute particles are attracted and the solvent particles are attracted to one another • So, before a solution can form, those attractions must be overcome • Process in which an ionic compound seperates into ions as it dissolves is called dissociation

  6. Dispersion of Molecular Compounds • The water in your saliva dissolves the sugar and flavoring in candy throughout your mouth • Sugar dissolves in water by dispersion, or breaking into small pieces that spread throughout the water • Both sugar and water are polar, therefore attract • When enough water molcules have surrounded the sugar molecule, sugar molecule breaks free and is pulled into solution

  7. Ionization of Molecular Compounds • HCl – molecular compound where hydrogen and chloride share an electron • When HCl gas dissolves in water, the H molecule is transferred to water • H30+ and Cl- are produced • When a neutral molecule gain or lose electrons it is known as ionization • This is a chemical change • Unlike dispersion and dissociation

  8. Properties of Liquid Solutions • Three physical properties of a solution that can differ from those of its solute and solvent are: • Conductivity • Freezing point • Boiling point

  9. Conductivity • Solid sodium chloride is a poor conductor • When it dissociates in water, the sodium and chloride ions are able to move freely • They will then conduct electricity

  10. Freezing Point and Boiling Point • MgCl2 is what is sometimes spread on icy roads • When it dissolves in melting ice, it dissociates into Mg2+ and Cl- • These ions are able to interfer with freezing process • Salted roads have a freezing point of -15°C

  11. Freezing Point and Boiling Point • Solute can also raise boiling point • ex. Coolant used in most car radiators • Adding ethylene glycol to water raises the boiling point • Solution helps prevent the engine from overheating • Also prevents the the liquid from freezing in the winter

  12. Heat of Solution • During the formation of a solution, energy is either released or absorbed • Can be described as either exothermic or endothermic • Dissolving sodium hydroxide in water is exothermic, releases heat • How it Works box explains how cold packs are used

  13. Heat of Solution • In order for a solution to form, all attractions must be broken • That requires energy • Formation of solutions, releases energy • The difference between these energies is called the heat of solution

  14. Factors Affecting Rates of Dissolving • Reates of dissolving depend on the frequency and energy of collisions • Formation of solutions, collisions occur between solute and solvent particles • Factors that affect the rate of dissolving include: • Surface area • Stirring • temperature

  15. Factors Affecting Rates of Dissolving • The greater the surface area of a solid solute, the more requent the collision are between the solute and the solvent particles • Increase surface area by breaking into smaller pieces • Stirring • Moves dissolved particles away from surface • Allows more collisions between solute and solvent

  16. Factors Affecting Rates of Dissolving • Increasing temperature is another way to speed up dissolving • Increase in temperature causes the particles to move faster • Both the number of collisions and the energy of these collisions increases • Goes into solution more quickly

  17. Review Quiz • 1. What do we call the substance whose particles are dissolved in a solution? • 2. What do we can the substance the dissolves the particles in a solution? • 3. When a neutral molecule gains or loses electrons, it is called ________? • 4. List two of the three factors that affect the rate of dissolving?

  18. 8.2 Solubility and Concentration

  19. Solubility • Solubility • The max amount of a solute that dissolves in a given amount of solvent at a constant temperature • Usually expressed in grams of solute in 100g of solvent • Solutions are described as: • Saturated • Unsaturated • Supersaturated

  20. Solubility • Saturated • Sugar is very soluble in water • At 20 degrees C you can dissolve 203.9 grams of sugar in 100g of water • What will happen if you try to dissolve more than that? • The extra sugar will not go into solution • The solution is already saturated • One that contains as much solute as the solvent can hold at a given temperature

  21. Solubility • Unsaturated • A solution that has less than the max amount of solute that can be dissolved • many beverages are unsaturated

  22. Solubility • Supersaturated • If you heat a solvent above the average temperature it can dissolve more solute • If you then carefully cool the solvent back to the average without jarring it, you may be able to keep the extra solute in the solution • Supersaturated solution • One that contains more solute than it can normally hold at a given temperature • Very unstable • If a tiny particle falls into a supersaturated solution, the extra solute may rapidly fall out

  23. Factors Affecting Solubility • Have you ever tried to wash oil or grease off your hands? • Will not come off in just water, but in soapy water it will wash off • Not soluble in water, but in soapy water it is • Three factors that affect solubility: • Polarity of the solvent • Temperature • pressure

  24. Factors Affecting Solubility • Polar and Nonpolar Solvents • Oil molecules are nonpolar, water is polar • Common guideline for predicting solubility is ‘like dissolves like’ • More likely to dissolve if solute and solvent are both polar or both nonpolar • Soap molecules have a polar and non polar end • Makes it easy to dissolve oil

  25. Factors Affecting Solubility • Temperature • In general the solubility of a solute increases when you increase the temperature of the solvent • When water temp increases, bubbles start to come out of the water • These are gas bubbles that are dissolved in water • Unlike most solids, gases usually become less soluble as the temperature of solvent increases

  26. Factors Affecting Solubility • Pressure • Incresing the pressure on a gas increases its solubility in a liquid • Pressure of carbon dioxide in a 12 oz can of soda at room temp can by two to three times atmospheric pressure

  27. Concentration of Solutions • Concentration • The amount of solute dissolved ina specified amount of solution • Can be expressed as: • percent by volume • percent by mass • molarity

  28. Percent by Volume • Often times on fruit juice bottles have a percentage of real fruit juice in it. • Ex. 27% real fruit juice • To calculate the concentration as a percent by volume: • Page 238

  29. Percent by Mass

  30. 8.3 Properties of Acids and Bases

  31. Identifying Acids • Acid • Compound that produces hydronium ions (H3O+) when dissolved in water. • Acids have certain chemical and physical properties that are similar • Sour taste • Reactivity with metals • Ability to produce color changes in indicators

  32. Sour Taste • Foods that taste sour often contain acids • Lemons, grapefruits, limes, and oranges all contain citric acid • Dairy products that have spoiled contain butyric acid • NEVER TEST AN ACID BY TASTING IT!

  33. Reactivity with Metals • Sometimes when you cover food with aluminum foil, it gets small holes in it, or the food starts to taste metallic • Foods with tomatoes contain citric acid which will react with aluminum (metal) • Single replacement reaction

  34. Color Changes in Indicators • Indicator • Any substance that changes color in the presence of an acid or base • Common idicator is litmus • Dye derived from plants called lichens • Blue litmus paper turns red in the presence of acid

  35. Identifying Bases • Base • A compound that produces hydroxide ions when dissolved in water • Have certain physical and chemical properties in common • Bitter taste • Slippery feel • Ability to produce color changes in indicators • Do not react with metals (usually) • Zinc and aluminum react vigorously with sodium hydroxide

  36. Bitter Taste • Have you ever tasted unsweetened chocolate? • Sometimes called baking chocolate… • Coco beans contain a base called theobromine that gives unsweetened chocolate its bitter taste • Cough syrups and other liquid medicines contain similar bases • Fruit flavorings are added to mask the bitter taste

  37. Slippery Feel • Wet soap and many cleaning supplies are slippery because they contain bases • When wet, some rocks feel slippery • Water dissolves compounds trapped in the rocks, producing basic solution

  38. Color Changes in Indicators • Bases turn red litmus paper blue. • Will change back to red if you put acid on the paper • Phenolphthalein is another example of an acid-base indicator • In solution containing base, solution is red • In solution containing an acid, colorless • Hydrangeas contain natural indicators • Color depends on acid/base soil • Acid soil – bluish-purple • Basic soil - pink

  39. Neutralization and Salts • Sometimes people squeeze lemon juice over fish • Fish is basic and can sometimes taste bitter • Lemon juice contains acids, makes it taste less bitter • Reaction between acid and base is called neutralization • Negative ions in acid combine with positive ions in base to form a salt • Hydronium ions combine with hydroxide ions to form water

  40. Proton Donors and Acceptors • Acids lose, or ‘donate’ protons • Bases accept, forming water, a neutral molecule • Water can act as either an acid or a base depending on what it is reacting with

  41. 8.4 Strength of Acids and Bases

  42. The pH Scale • Chemists use a scale from 0-14 to describe the concentration of hydronium ions in a solution • pH – measure of hydronium ion concentration • 7 indicates a neutral solution • Bases are greater than 7 • Acids are less than 7 • Lower the pH value, the higher the concentration of H30+

  43. Strong Acids • HCl is an example of a strong acid • When dissolved in water, there are about the same number of hydronium ions as there were molecules of HCl • When strong acids dissolve in water, they ionize almost completely • Other strong acids are sulfuric acid, and nitric acid

  44. Strong Bases • Strong bases dissociate almost completely in water. • Sodium hydroxide dissociates into sodium and hydroxide ions • Other strong bases are calcium hydroxide and potassium hydroxide

  45. Weak Acids and Bases • Weak acids and bases ionize or dissociate only slightly in water • It is important to know the difference between concentration and strength • Concentration: amount of solute dissolved in a given amout of solution • Strength: solute’s tendency to form ions in water • Buffers: solution that is resistant to large changes in pH

  46. Electrolytes • Electrolyte • Substance that ionizes or dissociates into ions when it dissolves in water • Resulting solution can conduct electricity • Sports drinks help restore the ions in your body • Strong acids/bases are strong electrolytes • Batteries contain electrolytes

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