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 AND HYDROGEN TOGETHER! What is the Chemical Formula for Water? So, is it organic?

Water is Important All chemical reactions occur in an aqueous environment What does THAT mean? Water is necessary for all chemical reactions to occur

What is weird about water? Remember Polarity? Water has opposite charges at opposite ends This gives water several unique properties 4

Water molecules display Polarity Polarity causes: Cohesion & Adhesion & Surface Tension 5

Cohesion – Water molecules stick to each other Adhesion – Water molecules stick to other molecules Surface Tension – The “tension” on the surface of water caused by cohesion Meniscus – The “curve” at the top surface of water in a graduated cylinder caused by adhesion 6

Dissociates Water is made up of two different atoms 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” in neutral  Water

The pH Scale

measures acidity/basicity 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 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. Each step on pH scale represents a factor of 10. pH 5 vs. pH 6 (10X more acidic) pH 3 vs. pH 5 (100X different) pH 8 vs. pH 13 (100,000X different) 13

Properties of acids and bases Acids – Sour taste – Turns blue litmus paper red – Reacts with some metals to produce H2 – Dissolves carbonate salts, releasing CO2 Bases – Bitter taste – Turns red litmus paper blue – Slippery to the touch Copyright © 2007 Pearson Benjamin Cummings. All rights reserved. 14

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

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 a 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 cells have a very narrow range of tolerance for pH 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 PAPER! The pH scale goes from 0 to 14—because [H+][OH-] = 10-14 18

Litmus Paper An indicator for pH Turns different colors in different liquids Acid Base (Alkali) Neutral

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