Acids and Bases http://www.chalkbored.com/lessons/chemistry-11/acid-bronsted.ppt 1

Water Water is an inorganic Molecule TO BE ORGANIC, A MOLECULE MUST HAVE CARBON IN IT What is the Chemical Formula for Water? So, it can’t be organic!

What is weird about water? Remember Polarity? We did the “pom-pom” lab an learned that some molecules are not linear Water has opposite charges at opposite ends This gives water several unique properties 3

Water molecules display Polarity And this Polarity causes: Cohesion & Adhesion & Surface Tension (Remember? We learned about the meniscus in a test tube) 4

Cohesion – Water molecules stick to each other Adhesion – Water molecules stick to other molecules Surface Tension – The “tension” (almost like a film) on the surface of water caused by cohesion Meniscus – The “curve” at the top surface of water in a graduated cylinder caused by adhesion 5

Dissociates Water is made up of two different elements 2 atoms of Hydrogen 1 atom of Oxygen When water dissociates (breaks apart) it forms two different ions Hydroxide (-OH) Hydrogen (+H) An ion is a molecule that has a charge Can be positive or negative

Swimming Pools Ever open your eyes in a swimming pool and they end up red and burning?

Heartburn? Have you ever had heartburn? Sometimes called Gerd It feels like your heart is on fire It is caused by stomach acid “climbing up” your esophagus

How do you get rid of it? Since heartburn is caused by stomach acid climbing up the esophagus… You neutralize it with “antacids” Which are basic!

Acids & Bases are Based on WATER! Depending on the amount of H+ or OH- ions, the “water” becomes either acidic or basic (aka alkaline) The pH scale determines the strength of the acid/base The pH scale runs from 0 -14 Low numbers are acidic High numbers are alkaline “7” is neutral  Water A comes before B

The pH Scale

pH scale measures acidity/basicity Søren Sorensen (1868 - 1939) ACID BASE 10x 100x 10x 10x 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 NEUTRAL Each step on pH scale represents a factor of 10 pH is defined as the negative base-10 logarithm of the hydrogen ion concentration pH = – log [H+] or [H+] = 10-pH Hydrogen ion concentration in pure water is 1 x 10-7 M at 25ºC; the pH of pure water is – log [1.0 x 10-7] = 7.00. pH decreases with increasing [H+] — adding an acid to pure water increases the hydrogen ion concentration and decreases the hydroxide ion concentration. Adding a base to pure water increases the hydroxide ion concentration and decreases the hydrogen ion concentration—pH increases with decreasing [H+]. pH scale runs from pH = 0 (corresponding to 1 M H+) to pH 14 (corresponding to 1 M OH–). Relationships between acidity, basicity, and pH: If pH = 7.0, the solution is neutral. If pH < 7.0, the solution is acidic. If pH > 7.0, the solution is basic. A change of 1,0 in the pH of a solution corresponds to a tenfold change in the hydrogen ion concentration because the pH scale is logarithmic. pH 5 vs. pH 6 (pH 5 is 10X more acidic) pH 3 vs. pH 5 (2 steps = 10x10 = 100X difference) pH 8 vs. pH 13 (5 steps = 10x10x10x10x10 = 100,000X difference) 12

Characteristics of Acids Taste Sour Conduct Electricity Corrosive, which means they break down certain substances. Many acids can corrode fabric, skin and wood Some acids react strongly with metals Turns blue litmus paper red Turn pH Paper Yellow  Red Depending on strength of acid

Characteristics of Bases aka - Alkalis Feel Slippery (Think SOAP!) Taste Bitter Corrosive (Just as corrosive as Acids!) Can conduct electricity. (Think alkaline batteries.) Do not react with metals Turns red litmus paper blue Turn pH paper Green  Blue Turn Phenolphthalein  Pink

Acids/Bases The lower the pH, the stronger the acid The higher the pH, the stronger the base Did you know the human body produces BUFFERS to maintain homeostasis Buffers help to neutralize acids and bases

Acid – Base Reactions A reaction between an acid and a base is called neutralization. An acid-base mixture is not as acidic or basic as the individual starting solutions.

Acid – Base reactions Acid + Base = Salt + Water! Each salt listed in this table can be formed by the reaction between an acid and a base. Neutralization

Neutralization To neutralize (counter-act) an acid, you add a base To neutralize (counter-act) a base, you add an acid The Buffers your body produces are either acidic or basic...

Buffers A buffer is a solution the helps return another solution to its proper pH A buffer can “soak up” excess H+ ions (acid) or “soak up” excess OH- ions (base) Your body produces buffers ALL THE TIME in order to maintain homeostasis Think about all of the acidic stuff you eat!

pH A strong acid A strong base SOURCE: http://en.wikipedia.org/wiki/Image:PH_scale.png#file pH 10-2 10-3 10-5 10-4 10-8 10-7 10-6 [H+] M 10-10 10-9 10-11 10-12 10-13 10-14 10-1 100 A strong acid A strong base Most living organisms have a very narrow range of tolerance for pH Remember…Each pH unit represents a factor of 10 difference in [H+] How do we figure out what’s an acid and what’s a base? LITMUS or pH PAPER! The pH scale goes from 0 to 14—because [H+][OH-] = 10-14 20

pH Paper An indicator for pH Turns different colors in different solutions Acid  Red Base (Alkali)  Blue Neutral  Lt. Green

Let’s Try It Out! We will be using Litmus paper to determine the pH of several household items!