Chapter 8 Solutions Acids and Bases 8 1

Chapter 8 Solutions, Acids, and Bases

8 -1 Formation of Solutions • Substance can dissolve in water three ways-by dissociation, dispersion, and ionization • A solute is a substance whose particles are dissolved in a solution. • The substance in which the solute dissolves is called the solvent. • Ex: Seawater • Solute = is the salt • Solvent = is the water

Solutes/Solvents • Solutes and solvents can take the form of a solid, liquid or gas. • The solution takes the state of the solvent.

Dissociation of Ionic Compounds • Dissociation is the process in which an ionic compound separates into ions as it dissolves. • For a solute to dissolve in water, the solute and solvent particles must attract one another. • Before a solution can form, the attractions that hold the solute together and the solvent together must be overcome

Dispersion of Molecular Compounds • Sugar dissolves in water by dispersion, or breaking into small pieces that spread throughout the water. • Ex: piece of candy disperses throughout your mouth • Water in saliva dissolves the sugar and flavoring in the candy.

Process of Dispersion • When enough water molecules surround a sugar molecule, the attractions between them are great enough to overcome the attractions holding the sugar molecule to the surface of the crystal. • The sugar molecule breaks free, and is pulled into solution by the water molecules, then another layer if sugar molecules is exposed to the water

Ionization of Molecular Compounds • The process in which neutral molecules gain or lose electrons is known as ionization. • Dissolving by ionization is a chemical change. • The solution that results contains new substances. • When a solute dissolves by ionization, the ions in solution are formed by the reaction of solute and solvent particles.

Example of Ionization • When water and hydrogen chloride form a solution, two molecular compounds react to form two ions. • Ions formed are H 3 O+ and Cl • Drawing

Answer the following Questions 1. What are three ways that substances can dissolve in water? 2. How does sugar dissolve in water?

8 -1 Continued Properties of Liquid solutions • Three physical properties of a solution that can differ from those of its solute and solvent are: 1. Conductivity 2. Freezing Point 3. Boiling Point

Conductivity • Solid sodium chloride is a poor conductor of electricity • Sodium chloride dissociates in water and the ions formed can move freely enabling them to conduct electricity

Freezing Point • The freezing point of water at sea level is 0 degrees Celsius • Example : icy roads are salted with magnesium chloride, the resulting solution can have a freezing point as low as -15 degrees Celsius

Boiling Point • A solute can raise the boiling point of the solvent • Example: the coolant used in most car radiators is a solution containing water and ethylene, which raises the boiling point. This helps the engine from overheating.

Heat of Solution • During the formation of a solution, energy is either released or absorbed. • In order for a solution to form, both the attractions among the solute particles and the attractions among the solvent particles must be broken. • Breaking attractions requires energy.

Heat of Solution Continued • As the solute dissolves, new attractions form between solute and solvent particles. • The formation of attractions releases energy. • The difference between these energies is known as heat of solution

Factors Affecting Rates of Dissolving • Factors that affect the rate of dissolving include: • Surface area • Stirring • Temperature

Surface Area • The greater the surface area of a solid solute, the more frequent the collisions are between solute and solvent particles. • More collisions result in faster rate of dissolving

Stirring • Stirring moves dissolved particles away from the surface of the solid, and allows for more collisions between the solute and solvent particles

Temperature • Increasing the temperature of the solvent speeds up the dissolving rate. • This causes its particles to move faster. • As a result, both the number of collisions and the energy of these collisions with solute particles increase. • The solute goes into the solution more quickly.

Beaker Breaker 1. List the three factors that affect the rate of dissolving. 2. Sugar dissolves in water by______, or breaking into small pieces that spread throughout the water

Section 8 -1 Review • Using your book complete the following questions: • Page 257 • Numbers 1, 2, 3, 4, 5

Section 8 -2 • The maximum amount of a solute that dissolves in a given amount of solvent at a constant temperature is called solubility • Ex: sugar in lemonade • Knowing the solubility of a substance can help you classify solutions based on how much solute they contain.

Solubility • • • Solutions are described as: saturated, unsaturated, Supersaturated depending on the amount of solute in solution.

Saturated Solutions • Table sugar is very soluble in water • A saturated solution is one that contains as much solute as the solvent can hold at a given temperature. • When a solution is saturated, the solvent is “filled” with solute. • If you add more solute, it will not dissolve.

Unsaturated Solutions • A solution that has less than the maximum amount of solute that can be dissolved is called an unsaturated solution. • Example: many beverages you drink are unsaturated solutions of sugar in water. • As long as the amount of solute is less than the solubility at that temperature, the solution is unsaturated

Supersaturated Solutions • A supersaturated solution is one that contains more solute than it can normally hold at a given temperature. • Supersaturated solutions are very unstable. • Ex: carrying a stack of books

Review Questions • What terms are used to describe solutions with different amounts of solute. • How does a supersaturated solution differ from a saturated solution?

How Cold Packs Work • Read page 233 in your book • Discussion

8 -2 Continued • • Factors Affecting Solubility Three factors that affect the solubility of a solute are: 1. The polarity of solvent 2. Temperature 3. Pressure

Polar and Nonpolar Solvents • Oil does not dissolve in water because oil molecules are nonpolar and water molecules are polar • A common guideline for predicting solubility is “like dissolves like” • Solution formation is more likely to happen when the solute and solvent are either both polar or both nonpolar

Temperature • In general, the solubility of solids increases as the solvent temperature increases. • Example: sugar added to cold tea verses hot tea • Gases usually become less soluble as the temperature of the solvent increases

Pressure • Increasing the pressure on a gas increases its solubility in a liquid • Carbonated beverages, uses pressure to force CO 2 to dissolve in the liquid • The pressure of CO 2 in a sealed 12 -ounce can of soda at room temp can be two to three times atmospheric pressure.

Concentrations of Solutions • The concentration of a solution is the amount of solute dissolved in a specified amount of solution • Concentrations can be expressed as percent by: volume, percent by mass, and molarity.

Percent by Volume • Percent by Volume = Volume of solute x 100% • Volume of solvent Example the volume of the solute is 10 L and the volume of the solvent is 30 L. What is the percent by volume?

Percent by Mass • Concentration expressed as a percent by mass is more useful when the solute is a solid. • Percent by mass = Mass of solute x 100% • Mass of solution • Example: Suppose you have 100 grams of a solution of sugar in water. After allowing the water to evaporate, 15 grams of sugar remains. What is the percent by mass?

Molarity • Molarity is the number of moles of a solute dissolved per liter of a solution. • Molarity = moles of solute • Liters of solution x 100%

Example of Molarity • To make 1 -molar (1 M) of solution of sodium chloride in water 1. First calculate the molar mass of the solute (Na. Cl) = _____ 2. If 58. 5 grams of sodium chloride is mixed with enough water to make one liter of solution, the resulting solution is 1 -molar.

Complete the following Questions 1. )What are three ways that substances can dissolve in water? 2. What physical properties of a solution differ from those of its solutes and solvents? 3. How does the formation of a solution involve energy? 4. What factors affect dissolving rates? 5. Identify the processes by which sugar crystals and hydrogen chloride gas dissolve in water.

8 -3 Properties of Acids and Bases • There are several differences among acidic solutions, basic solutions, and solutions that have properties neither an acid or nor a base

Identifying Acids • An acid is a compound that produces hydronium ions (H 3 O+) when dissolved in water. • Ex: HCl + H 2 O H 3 O+ + Cl • Some general properties of acids include sour taste, reactivity with metals, and ability to produce color changes in indicators

Sour Taste • Foods that taste sour often contain acids • Ex: lemons, grapefruits, limes, and oranges all contain citric acid. • Vinegar contains acetic acid. • Dairy products that have spoiled contain butyric acid

Reactivity with Metals • When you use aluminum foil to cover a bowl of leftover spaghetti sauce or other foods containing tomatoes the foil often turns dark. • Tomatoes contain citric acid, which reacts with metals such as aluminum

Reactivity with Metals • The reaction between an acid and a metal is an example of single replacement reaction. • Ex: Zinc is added to hydrochloric acid. Zn +2 HCl H 2 + Zn. Cl 2 • As zinc replaces hydrogen in hydrochloric acid, hydrogen gas and zinc(II) chloride is produced

Color Changes in Indicators • An indicator is any substance that changes color in the presence of an acid or base. • One of the most common indicators used is litmus, a kind of dye derived from plants called lichens. • Litmus paper is made by coating strips of paper with litmus. • Blue litmus paper turns red in the presence of an acid.

Testing Acids on litmus paper • Vinegar – • Observations • HCl – • Sulfuric Acid – • Acetic Acid -

Identifying Bases • Sodium hydroxide, Na. OH is an example of a base. • A base is a compound that produces hydroxide (OH-) when dissolved in water. • Na. OH Na+ + OH-

Bases • Bases have certain physical and chemical properties that you can use to identify them. • Some general properties of bases include bitter taste, slippery feel, and ability to produce color changes in indicators

Properties of Bases • Bitter Taste • Slippery Feel • Color Changes in indicators

Bitter Taste • Baking chocolate (without the sugar) • Cough syrups and other liquid medicines

Slippery Feel • Bases feel slippery. • Wet soap and many cleaning products that contain bases are slippery to the touch. • When wet, some rocks feel slippery because water dissolves compounds trapped in the rocks, producing a basic solution.

Color changes in Indicators • Bases turn red litmus paper blue. • Observations of bases • Na. OH – • Ba(OH)2 • NH 4 OH-

Flowers • Hydrangeas color changes based on whether they are grown in acidic or basic soil • Acidic – flowers are bluish-purple • Basic – flowers are pink

End of 8 -3 Neutralization and Salts • Fish contains bases that can leave a bitter taste. • Lemon juice contains an acid called citric acid. • Squeezing lemon juice on fish makes it taste less bitter • The reaction between an acid and a base is called neutralization

Neutralization • During neutralization, the negative ions in an acid combine with the positive ions in a base to produce an ionic compound called a salt • The hydronium ions from the acid combine with the hydroxide ions from the base to produce water. • The neutralization reaction between an acid and a base produces a salt and water.

Example of neutralization • (H 3 O+ + Cl- ) + Na+ + OH- ) 2 HOH + (Na+ + Cl-) acid base water salt Other common salts that are produced during neutralization are: 1. Potassium chloride – KCl – salt substitute 2. Potassium iodide – KI- added to table salt to prevent iodine deficiency 3. Magnesium Chloride – Mg. Cl 2 – De-icer for roads

Proton Donors and Acceptors • Acids lose or “donate” protons • Bases “accept” protons, forming water, a neutral molecule. • Acids can be defined as proton donors, and bases can be defined as proton acceptors. • Example water can act either as an acid or base depending on the compound with which it reacts.

Water acting as an acid and a base • Complete the following examples from the board.

8 -4 Strengths of Acids and Bases • Chemists use a number scale from 0 to 14 to describe the concentration of hydronium ions in a solution. It is known as the p. H scale. • The p. H of a solution is a measure of its hydronium ion concentration.

p. H scale • • A p. H of 7 indicates a neutral solution. Acids have a p. H less than 7 Bases have a p. H greater than 7 See Figure 22

p. H scale • Water is neutral because it contains small but equal concentrations of hydronium ions and hydroxide ions. • The lower the p. H value, the greater the H 3 O+ ion concentration in solution is. • The higher the p. H value, the lower the H 3 O+ ion concentration is.

Strong Acids and Bases • When certain acids and bases dissolve in water, the formation of ions from the solute almost goes to completion. Such acids and bases are classified as strong.

Strong Acids • When strong acids dissolve in water, they ionize almost completely. • Ex: HCl = hydrochloric acid • H 2 SO 4 = sulfuric acid • HNO 3 = nitric acid

Strong Bases • Strong bases dissociate almost completely in water. • Examples of strong bases: • Na. OH – sodium hydroxide • Ca(OH)2 - calcium hydroxide • KOH – potassium hydroxide

Beaker Breaker 1. Acids have a p. H range from ____to ______ 2. Name one property of a base ________ 3. Compare the p. H values of acids, bases, and pure water.

Weak Acids and Bases • Weak acids and bases ionize or dissociate only slightly in water • The citric acid in orange juice and the acetic acid in vinegar are weak acids. • Toothpaste and shampoo contain weak bases.

Concentration verses strength • Concentration is the amount of solute dissolved in a given amount of solution. • Strength refers to the solute’s tendency to form ions in water.

Weak Acids • A weak acid forms fewer hydronium ions than a strong acid of the same concentration. • A weak acid has a higher p. H than a strong acid of the same concentration.

Weak Bases • Follows the same concept as weak acids. • Example is NH 3 (ammonia) because when it dissolves in water, very little of it ionizes.

Buffers • Weak acids and bases can be used to make buffers. • A buffer is a solution that is resistant to large changes in p. H. • Buffers can be prepared by mixing a weak acid and its salt or a weak base and its salt.

Electrolytes • An electrolyte is a substance that ionizes or dissociates into ions when it dissolves in water. • The resulting solution can conduct electric current. • Electrolytes in sports drinks help restore the balance of ions in your body.

Electrolytes • Strong acids and bases are strong electrolytes because they dissociate or ionize almost completely in water. • Ex: sodium hydroxide (Na. OH) is a strong electrolyte that produces many ions in water. • Acetic acid is a weak electrolyte because it only partially ionizes.

Examples of Electrolytes • Batteries and other portable devices that produce electricity also contain electrolytes. • Car batteries use lead plates in combination with the electrolyte sulfuric acid to produce electricity. • Space shuttles use devices called fuel cells • Fuel cells use the strong base potassium hydroxide as an electrolyte.

Testing strong weak acids verses strong weak bases on litmus paper • Observations Test #1 HCl – strong or weak acid or base Test #2 Na. OH – strong or weak acid or base Test# 3 CH 3 COOH – strong or weak acid or base Test#4 NH 3 + - strong or weak acid or base