Solutions, Acids, and Bases

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

• 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

• 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.

• 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

• 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.

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

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

• 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

• 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

• 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

• 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.

• 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.

• 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 that affect the rate of dissolving include:
• Surface area
• Stirring
• Temperature

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

• 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.

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

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

• 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.

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

• 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.

• 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

• 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

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

• Read page 233 in your book
• Discussion

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

• 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

• 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

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

• 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 = 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?

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

• To make 1-molar (1M) of solution of sodium chloride in water
1. First calculate the molar mass of the solute (NaCl) = _________
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.

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.

• There are several differences among acidic solutions, basic solutions, and solutions that have properties neither an acid or nor a base

• 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

• 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

• 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

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

• 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.

• Observations
• Vinegar –
• HCl –
• Sulfuric Acid –
• Acetic Acid -

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

• 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

• Bitter Taste
• Slippery Feel
• Color Changes in indicators

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

• 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.

• Bases turn red litmus paper blue.
• Observations of bases
• NaOH –
• Ba(OH)
2-
• NH
4
OH-

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

• 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

• 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.

• (H O + + Cl ) + Na + + OH )  2HOH + (Na + + Cl )
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 – MgCl
2
– De-icer for roads

• 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.

• Complete the following examples from the board.

• Chemists use a number scale from 0 to 14 to describe the concentration of hydronium ions in a solution. It is known as the pH scale.
• The pH of a solution is a measure of its hydronium ion concentration.

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

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

• 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.

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

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

1. Acids have a pH range from ________to
___________
2. Name one property of a base
_______________
3. Compare the pH values of acids, bases, and pure water.

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

• A weak acid forms fewer hydronium ions than a strong acid of the same concentration.
• A weak acid has a higher pH than a strong acid of the same concentration.

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

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

• 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.

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

• 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.

• Observations
Test #1 HCl – strong or weak acid or base
Test #2 NaOH – 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