1.2 Acids and Bases

Overview Properties and examples of pH Neutralization reactions Lab Acids, bases, neutral solutions pH The pH scale Measuring pH Neutralization reactions Lab Acid rain Causes, impacts, and treatment

First... Brainstorm with your table partner: Some properties of acids, bases, and neutral solutions Examples of each solution How they interact with one another, the environment, etc.

Properties of Acids Dissolve in water Has more hydrogen ions (H+) than hydroxide ions (OH-) present Taste sour, and can cause a stinging feeling Fun fact: the liquid in your stomach is actually very acidic!

Properties of Bases Soluble in water Has more hydroxide ions (OH-) than hydrogen ions (H+) present Feel slippery and taste bitter Fun fact: bases do not react with metals! This is what makes them such effective drain cleaners

Neutral Solutions Neither acidic nor basic

pH: The Power (or Potential) of Hydrogen The pH Scale pH is the measure of hydrogen ions, H+, in a solution If the pH is less than 7 (i.e. 0-6) the solution is ACIDIC If the pH is greater than 7 (i.e. 8-14) the solution is BASIC A pH of 7 means the solution is NEUTRAL The pH Scale

Strong vs. Weak Acids and Bases Strong acids have a pH <2 Strong bases have a pH >12 Rule: There is a 10-fold difference between the numbers on the pH scale Meaning: A pH of 2 will be 10 times more acidic than a pH of 3 A pH of 9 will be 10 times more basic than a pH of 8

Litmus Paper Measuring pH pH Paper pH Meter Uses plant compounds called lichens Tells us whether something is an acid or a base, does NOT tell what the pH is Acids turn blue litmus paper red Bases turn red litmus paper blue pH paper (universal indicator) Gives an approximate (i.e. whole numbers such as 1, 2, 3, etc.) reading of the pH When dipping pH paper into a solution, the paper will change its colour-- this colour will indicate a specific pH! pH meter (digital tool) Gives an exact reading (i.e. decimal numbers) of the pH by measuring the ions present in a solution pH Paper pH Meter

Neutralization Reactions Acids and bases can be neutralized by allowing them to react with each other These reactions will form a salt and water (which are less harmful than the reactants!): Strong acid + Strong base → Neutral Strong acid + Weak base → Acidic Weak acid + Strong base → Basic Weak acid + Weak base → it depends on how weak the acid and base are relative to one another

Lab Time!

Video

Wrapping Up: Acid Rain Normal pH of rainwater is around 5.4 Slightly acidic because of CO2 which reacts with water to form carbonic acid Acid rain usually has a pH of around 3-4 Industrial factories, coal-fired power plants, and vehicle emissions give off sulfur dioxide (SO2) and nitrogen oxides (NOx) Water molecules in the air will react with these gases to produce sulfuric and nitric acids These may all contribute to acid rain

Acid Rain Destroys lakes and streams Kills aquatic organisms and plants Buildings, and other structures such as statues deteriorate How is this treated? One method: Neutralization reaction! Calcium hydroxide, Ca(OH)2 (aka ‘lime’), is added to lakes and streams This reacts with the acids present to form a salt and water Base + Acid → Salt + Water If all of the acids and bases are used up, the solution becomes neutral!