Solutions, Acids & Bases Physical Science: Concepts in Action Chapter 8 Solutions, Acids & Bases

8.1 Formation of Solutions Objectives: 1. Describe how a substance can dissolve in water by dissociation, dispersion or ionization 2. Describe how physical properties of a solution can differ from those of its solute and solvent 3. Identify energy changes that occur during formation of a solution 4. Describe factors affecting the rate at which a solute dissolves in a solvent

Dissolving: Dissociation, Dispersion or Ionization Substances can dissolve in water by three ways: 1. dissociation 2. dispersion 3. ionization Definition: dissociation is the process by which an ionic compound separates into ions Ex: NaCl

Phet Salts & Solubility https://phet.colorado.edu/en/simulation/legacy/soluble-salts

Definition: dispersion is the process by which a covalent compound breaks into small pieces that spread throughout the water Ex: sugar dissolves in water Definition: ionization is the process by which neutral molecules (acids or bases) gain or lose electrons (forming ions) Ex: hydrogen chloride gas & water react to form hydronium ion (H3O+) and chlorine ion (Cl-)

Physical Properties: Solute & Solvent Definition: a solute is a substance whose particles are dissolved in a solution (often a solid) Definition: a solvent is the substance in which the solute dissolves (often a liquid) Solutes and solvents can take the form of solids, liquids or gases The solution takes the state of the solvent

Three physical properties of a solution that can differ from those of its solute and solvent are conductivity, freezing point & boiling point Definition: conductivity is the ability of a solution to conduct electricity Ex: NaCl is a poor conductor until it is placed in water & dissociates

Phet Sugar and salt solutions (conductivity） https://phet.colorado.edu/en/simulation/legacy/sugar-and-salt-solutions

Definition: the freezing point is the temperature at which a liquid becomes a solid Freezing point is changed with the addition of ionic compounds like MgCl2 or other ionic compounds The freezing point is lowered when ionic compounds are added

Definition: the boiling point is the temperature a liquid substance becomes a gas Coolants used in radiators (ethylene glycol, a molecular substance) raise the boiling point of water & keeps the engine from overheating Formation of new solutions by the addition of ionic or molecular compounds requires an energy change

Ted-ed Under the hood: The chemistry of cars - Cynthia Chubbuck http://ed.ted.com/lessons/under-the-hood-the-chemistry-of-cars-cynthia-chubbuck/review_open#question-5

Energy Changes & Solution Formation During formation of a solution, energy is either released or absorbed (Hot vs. Cold Packs) The process is endothermic or exothermic Forming attractions releases energy (exothermic) Breaking attractions requires or absorbs energy (endothermic)

Demo Exo vs Endo heats of Solution 1g Kcl in 5mL H2O 5mL alcohol (or 1g NaOH) in 5mL H2O

Factors that Affect Dissolving Rate Factors that affect the rate of dissolving include surface area, stirring and temperature Dissolving takes place at the surface The greater the surface area, the faster the dissolving Stirring or shaking makes a substance dissolve faster by increasing the surface area exposed to the solvent

8.2 Solubility and Concentration Objectives: 1. Define solubility and describe factors affecting solubility 2. Classify solutions as unsaturated, saturated or supersaturated

Solubility & Factors Affecting Solubility Definition: solubility is the maximum amount of a solute that dissolves in a given amount of solvent at a constant temperature Solutions are classified as saturated, unsaturated or supersaturated The classification depends on the amount of solute in solution

3 types of solutions Definition: a saturated solution is one that contains as much solute as the solvent can hold at a given temperature Definition: an unsaturated solution has less than the amount of solute that can be dissolved Definition: a supersaturated solution contains more solute than the solution can normally hold at a given temperature

Unsaturated vs. Sat.

Sodium Acetate

Vids Supersaturated solution- hot ice https://www.youtube.com/watch?v=BLq5NibwV5g Rock candy crystallization https://www.youtube.com/watch?v=VpOU0Fo7QfU

Factors affecting solubility Polar and Nonpolar solvents “Like dissolves like” Temperature Inc. in solubility for solids, dec. for gases Pressure Inc. in pressure forces gas bubbles to dissolve

Polar and Nonpolar solvents “Like dissolves like” Polar solvents dissolve polar solutes

Temperature Inc. in solubility for solids, dec. for gases

Pressure Inc. in pressure forces gas bubbles to dissolve

Concentration of Solutions Percent by volume Liquid in liquid / gas in gas Percent by mass Solid in liquid Molarity Used for chemical reactions

Percent by volume

Percent by mass

Molarity 1 molar solution Molar Mass NaCl = 58.44 g Molar Mass Sugar c12H22O11 = 342 g

A natural indicator Indicator – blueberry juice Acids and bases – Acids are sour and reacts with metal; bases are bitter and slippery Lemon juice, Vinegar, Window cleaner, Baking soda

8.3 Properties of Acids and Bases Objectives: 1. Define acid and describe the general properties of an acid 2. Define base and describe some of the general properties of a base

Acids Definition: an acid is a compound that produces hydronium ions (H3O+) when dissolved in water Some general properties of acids include sour taste, reactivity with metals, and ability to produce color changes in indicators Definition: an indicator is any substance that changes color in the presence of an acid or a base

Bases Definition: a base is a compound that produces hydroxide ions (OH-) when dissolved in water Some general properties of bases include bitter taste, slippery feel, and ability to produce color changes in indicators

Neutralization and salts

Ted-ed The strengths and weaknesses of acids and bases - George Zaidan and Charles Morton https://www.youtube.com/watch?v=DupXDD87oHc

Proton Donors and acceptors Acids: proton donors Ex: HCl, HNO3, H2CO3 Bases: proton acceptors - or donates (OH-) Ex: NH3, NaOH, KOH

8.4 Strengths of acids and bases The pH scale Strong vs. weak acids and bases Buffers Electrolytes

PH video https://www.youtube.com/watch?v=ckbsHM2igT0

Strength of Acids and Bases Objective: 1. define pH and relate pH to hydronium ion concentration ----------------------------------------------- Definition: pH of a solution is a measure of its hydronium ion concentration

A pH of 7 indicates a neutral solution Water is the standard for pH 7 Water self-ionizes and has a concentration of 1.0 x10-7 M hydronium ions pH scale runs from 0 – 14 The lower the pH, the higher the higher the hydronium ion concentration

The higher the hydronium ion concentration, the more acidic the substance is A high pH value means a low H3O+ concentration The lower H3O+ concentration, the more basic or alkaline the solution is

PH 1 = H3O+ conc. of 1 x 10-1 PH 2 = H3O+ conc. of 1 x 10-2 Therefore, each the difference between each pH level is 10x, not 2x

Phet PH scale https://phet.colorado.edu/en/simulation/ph-scale

Strong acids dissociate completely in water Ex: HCl Strong vs Weak acids and bases Strong acids dissociate completely in water Ex: HCl Weak acids dissociate partially in water Ex: H2CO3 “Strong” acids are not necessarily strong, and “weak” does not necessarily mean weak; this depends on concentration of acid used

Comparing “strong” vs. “weak” acids Mini-lab, 1M Hcl, indicator and vinegar Comparing “strong” vs. “weak” acids Making pH 3 solutions with a weak acids and a strong acid Compare the amount of strong acid and weak acid you had to add; even though you’re trying to make equal pH solutions why aren’t the amount of each acid you use equal?

Buffer – a solution that is resistant to large changes in pH

Buffers can act as acid or a base Buffers are present in human body Weak acids and bases can act as “buffers” because the undissociated molecules buffer the change in pH when other acids/ bases are added Buffers can act as acid or a base Buffers are present in human body

All about that base https://www.youtube.com/watch?v=IAJsZWhj6GI

Electrolytes Electrolyte – a substance that ionizes or dissociates into ions when it dissolves in water Electrolytes carry electricity and electrical potential across cell membranes

Electrolyte video https://www.youtube.com/watch?v=l3VWb0mUS7Y