Water and Aqueous Solutions

Unit 4 Section 3: Aqueous Systems & Solutions

Multiple Choice

Change of a gas directly into a solid

• Sublimation

• Condensation

• Evaporation

• Deposition

Dropdown

You can tell a chemical is an ionic compound because it contains a ​ ​

Select answer

bonded with a non-metal

Match

Match the point defect to its description

• Interstital

• Substitution

• Vacancy

Anxtra atom is in a spot it doesn't belong

An atom is in the wrong spot

An atom is missing

• Anxtra atom is in a spot it doesn't belong

• An atom is in the wrong spot

• An atom is missing

Lesson Objectives

• Describe the role polarity plays in hydrogen bonding between water molecules

  • Surface Tension, boiling point, the formation of ice

• Demonstrate the process of solvation within an aqueous solution

• Describe the different types of solutions and how they are formed

​Water and Hydrogen Bonding

• Water Molecules are highly polar and strongly attracted to each other

• Affects many of the properties of water

  • Surface Tension

  • Boiling Point

  • Ice Properties

​

​Surface Tension

• Water naturally forms a spherical shape

  • Hydrogen Bonding pulls water molecules into a pattern where the oxygen on one molecule attracts the hydrogen on another

  • Molecules on the outer edge are only pulled inward

    • Creates a tension that acts like a membrane, holding water together

• Surface Tension: the tension of the surface film of a liquid caused by the attraction of the particles which tends to minimize surface area

​Surface Tension

​Surface Tension

• Surface tension is affect by various things

  • The type of substrate​ (surface)

    • Non-polar substrate does not pull hard on water, so drops remain rounded

      • Round drops roll easier

      • Can be taken advantage of to self clean

        • Example: Louts Leaf

​Surface Tension

• Surface tension is affect by various things

  • The type of substrate​ (surface)

    • Polar substrates pull on water molecules and flatten them

​Surfactants

• Surfactant: A substance that decreases surface tension

  • Has a polar end and a non-polar end

  • Water bonds with the polar end, weakening the hydrogen bonding between water molecules and reducing surface tension

  • More surfactant = flatter drops

  • Used in Soaps and detergents

​Hydrogen Bonding and Boiling Point

• Most molecular compounds are gases at STP and have low boiling points

• Water has a relatively high boiling point of 100 °C

  • Hydrogen Bonds form between molecules

  • Each water molecule can form more hydrogen bonds because it has two electron pairs

​Structure of Water and Ice

• Ice is unique as a solid

  • Expands and becomes less dense as it freezes

    • Hydrogen bonding between water molecules pushes each molecule into a repeating pattern of hexagons

  • Ice on the surface can act as an insulator and stop freezing of water beneath the surface

Multiple Choice

The tension that forms on the outer surface of a liquid and acts like a membrane is known as

• Surfactants

• Surface Tension

• Hydrogen Filming

• Waxing

Dropdown

Water molecules are attracted to one another through hydrogen bonding because they are highly​

Select answer

Multiple Choice

The lone electron pairs on water lower the boiling point of water

• True

• False

Multiple Choice

Ice floats because the hexagon shape of ice crystals are less dense than water

• True

• False

​Aqueous Solutions

• Solutions: Mixtures of substances where one substance dissolves in another

  • Solvent: The substance that is used to dissolve

    • Water is the universal solvent

    • Aqueous Solution: Solution where water is the solvent

  • Solute: The substance that dissolves

    • Usually ions, but sometimes polar molecules​

    • Polarity of molecules determines how they behave as a solute

      • Non-polar compounds don't dissolve

​Electrolytes and Non-Electrolytes

• Electrolytes: Compounds that conduct electrical current when dissolved in water

  • All Ionic Compounds are electrolytes and carry a charge

  • More ions make a strong electrolyte, Fewer make weak electrolytes

• Non-Electrolytes: A compound that does not conduct electric current in solution or a molten state

​Hydrates

• Hydrates: a solid crystalline compound that contains water molecules as an integral part of its crystal structure

  • Water can be removed or gained through pressure changes

    • Efflorescence: the loss of water by a hydrate

  • Hydrates with a low vapor pressure can remove water from a substance

    • Desiccant: A substance that absorbs moisture from the air

Match

Match the following words with their definitions

• Solute

• Solvent

• Electrolytes

• Non-Electrolytes

• Hydrates

Substance that dissolves

Substance that is used to dissolve

Compounds that conduct Electricty

Compounds that do not conduct electricity

Solid Crystals that contain water molecules in their crystal structure

• Substance that dissolves

• Substance that is used to dissolve

• Compounds that conduct Electricty

• Compounds that do not conduct electricity

• Solid Crystals that contain water molecules in their crystal structure

Multiple Choice

When a gas loses energy and enters the liquid phase ...

• Evaporation occurs

• Condensation occurs

• Freezing occurs

• Melting occurs

Multiple Choice

In which state of matter are the molecules moving the slowest?

• Solid

• Liquid

• Gas

• All are equal

Multiple Choice

Which state of matter has defined volume but not shape?

• Solid

• Liquid

• Gas

​Solution Formation

• Dissolution Rate: The rate at which a solute dissolves​

  • Depends on several factors

    • Size of a solute: Smaller particles have a greater surface area to be touched by the solvent

    • Temperature: Increases the speed of molecules

    • Agitation​: Breaks apart clumps of solute and increases kinetic energy

​Solubility

• Every solvent has a limit to how much of a solvent it can dissolve

• Solubility: the amount of solute that can be added to a solvent in specific conditions

  • Three types of solutions

    • Unsaturated: the solution contains less than the maximum amount of solute

    • Saturated: The solution contains the exact amount of solute

    • Super Saturated: The solution contains more than the maximum amount of solute

      • Extra solute crystalizes in the container

​Supersaturation

• Supersaturation leads to the growth of crystals of the solute

  • By raising the temperature to induce higher solubility, you can eventually cool a solution with more dissolved than normal

  • Crystallization Can be induced with the addition of a seed crystal ​

Dropdown

You make a pitcher of kool aid. You use the normal amount of water but only use half of the packed and the liquid is light colored with no taste. This is an example of a ​

Select answer

Solution

Dropdown

You take the earlier pitcher of Kool aid and add an additional three packets to the pitcher. Kool aid powder is sitting on the bottom of the pitcher. This is an example of a ​

Select answer

Solution

Dropdown

You take the earlier pitcher of Kool aid and add water until all the koolaid powder dissolves, but the solution maintains a bright color and taste. This is an example of a ​

Select answer

Solution

​Solubility and Temperature

• The Temperature of a solution affects how much solute can be dissolved in it.

• Solubility Curve: a graph of the solubility as a function of temperature

  • Line tells you the amount of solubility at a given temperature

  • Can help predict when a solution may be unsaturated, saturated, or supersaturated

Experience Chemistry | Lesson 4.6

Multiple Choice

When the temperature of the solvent is 50° C, approximately how many grams of sodium acetate will dissolve?

• 10

• 50

• 100

• 150

​Solubility of Gases

• Gases work the opposite of solids

  • Increasing temperature causes less gas to be dissolved in a solvent

  • Causes many enviornmental problems

    • As water temperatures rise, less oxygen gas is able to be contained in the water

      • Hypoxic Zones: areas where the amount of oxygen in water is so low, animal life suffocates

​Solubility and Pressure

• Pressure has little effects on the solubility of liquids and solids, but can greatly change the solubility of gases

  • Solubility increases as the pressure of a solution increases​

​Henry's Law

• The mathematical relationship between Solubility and Pressure

  • Can be used to predict solubility at different pressures​

• S= solubility, P= Pressure​

  • You can use any unit for pressure, but both the Initial and final pressure need to be in the same un​its

​Henry's Law Sample Problem 1

• If the solubility of a gas in water is 0.77g/L at 3.5 atm of pressure, what is its solubility at 1.0 atm of pressure if the temperature remains constant?

  • Step 1: Identify the information you know

    • S₁ = 0.77 g/L

    • P₁ = 3.5 atm

    • S₂ = ?

    • P₂ = 1.0

  • Step 2: Substitute your known information into Henry's Law​ and solve for the unknown

​Henry's Law Sample Problem 2

• The solubility of a gas in water is 0.16 g/L at 104 kPa. What is the solubility when the pressure of the gas is increased to 288 kPa?

  • Step 1: Identify the information you know

    • S₁

    • P₁

    • S₂

    • P₂​

​Henry's Law Sample Problem 2

• The solubility of a gas in water is 0.16 g/L at 104 kPa. What is the solubility when the pressure of the gas is increased to 288 kPa?

  • Step 1: Identify the information you know

    • S₁ = 0.16

    • P₁ = 104

    • S₂ = ?

    • P₂ = 288

  • Step 2: Plug ​your values into Henry's law and Solve

​Types of Mixtures

• Mixtures are combinations of 2 or more different substances

  • Solutions are known as Homogenous mixtures

    • Have a uniform composition so you can't see the separate parts of them

  • Heterogenous Mixtures: mixtures that are not uniform in composition

​Types of Heterogenous Mixtures

• Two types:

  • Colloids: small molecules are clumped together throughout a liquid medium

    • Example: Milk

  • Suspensions: a mixture where the particles will separate out on their own over time

    • Has larger particles

Multiple Choice

What is a mixture?

• The combination of two or more substances.

• An ingredient.

• A liquid.

• A gas.

Multiple Choice

Is tea a mixture or a solution?

• Mixture

• Solution

Multiple Choice

Is fruit salad a mixture or solution?

• Mixture

• Solution