Section 2.5—Characteristics of Acids and Bases Now that we know what acids are, how do they act?

Characteristics of Acids & Bases Produce H3O+1 (hydronium ion) in water Produce OH-1 (hydroxide ion) in water Tastes sour Tastes Bitter React with active metals to form hydrogen gas Feels slippery

Strength versus Concentration

Review of how acids produce ions - water acid Hydrogen cation with some anion

Review of how acids produce ions - +1 H O

Review of how acids produce ions - +1 H O Hydronium ion Anion

Strong versus Weak Acids How many hydronium ion – anion pairs can you find? - + - 3 + How many intact acid molecules can you find? + - 1 Strong acid Most of the acid molecules have donated the H+1 to water

Strong versus Weak Acids + How many hydronium ion – anion pairs can you find? 1 How many intact acid molecules can you find? - 3 Weak acid Only a few of the acid molecules have donated the H+1 to water

Concentrated versus Dilute solvent solute Lower concentration Not as many solute (what’s being dissolved) particles Higher concentration More solute (what’s being dissolved) particles

Combinations of Concentration & Strength Concentrated Dilute Strong A lot of acid added & most dissociates Not much acid added, but most of what’s there dissociates Weak A lot of acid added, but most stays together Not much acid added and most of what is there stays together

Other notes All of the same ideas apply to bases as well (concentration and strength) Many people think all acids are dangerous and all bases are more safe Vinegar is an acid we eat…some of them are safe! Sodium hydroxide is a very caustic base…not all of them are less harmful than acids! The stronger and acid or base is (and the more concentrated it is), the more dangerous it is for you

pH

pH Scale Is a scale to measure the acidity of a sample 1 14 7 Highly acidic Very basic (not acidic) neutral 7 Chapter 6 will give more detail about how pH is calculated!

Ways to measure pH Indicators change color based on pH Liquid indicators – various indicators change colors at different pH’s Universal indicator – a combination of liquid indicators to produce a “rainbow” changing colors at several pH’s Paper Indicators Paper with a liquid indicator on it (Litmus paper or pH paper) pH meters or pH probes Electronically determine pH and give a read-out

Common pH indicators This picture © 1998 David Dice

pH of common substances 0.1M HCl 1 Stomach contents 2 Vinegar 2.9 Soda pop 3 Grapes 4 Beer 4.5 Pumpkin pulp 5 Bread 5.5 Intestinal contents 6.5 Milk Urine 6.6 Bile 6.9 Saliva 7 Blood 7.4 Eggs 7.8 0.1M NH3 (aq) 11.1 0.1M NaOH 13