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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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Chapter 8

Chapter 8

Solutions, Acids, and Bases


8 1 formation of solutions

8.1 Formation of Solutions


Dissolving

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


Dissolving1

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


Dissociation of ionic compounds

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


Dispersion of molecular compounds

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


Ionization of molecular compounds

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


Properties of liquid solutions

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


Conductivity

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


Freezing point and boiling point

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


Freezing point and boiling point1

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


Heat of solution

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


Heat of solution1

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


Factors affecting rates of dissolving

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


Factors affecting rates of dissolving1

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


Factors affecting rates of dissolving2

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


Review quiz

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?


8 2 solubility and concentration

8.2 Solubility and Concentration


Solubility

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


Solubility1

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


Solubility2

Solubility

  • Unsaturated

    • A solution that has less than the max amount of solute that can be dissolved

      • many beverages are unsaturated


Solubility3

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


Factors affecting solubility

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


Factors affecting solubility1

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


Factors affecting solubility2

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


Factors affecting solubility3

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


Concentration of solutions

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


Percent by volume

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


Percent by mass

Percent by Mass


8 3 properties of acids and bases

8.3 Properties of Acids and Bases


Identifying acids

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


Sour taste

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!


Reactivity with metals

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


Color changes in indicators

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


Identifying bases

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


Bitter taste

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


Slippery feel

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


Color changes in indicators1

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


Neutralization and salts

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


Proton donors and acceptors

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


8 4 strength of acids and bases

8.4 Strength of Acids and Bases


The ph scale

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+


Strong acids

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


Strong bases

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


Weak acids and bases

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


Electrolytes

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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