pH scale and Neutralization Reactions (P296-297) Lesson 13 September 15th, 2010

The Strength of Acids and Bases The strength of acids and bases are not all equal. Some acids and bases are safe enough to eat while others can eat through clothing and metal.

The Strength of Acids and Bases Some acids and bases are classified as being strong while others are called weak. -Strong acids and bases are extremely reactive and corrosive. -Weak acids and bases are mostly unreactive and corrosive.

The Strength of Acids and Bases The strength of an acid is determined by its ability to produce hydrogen ions (H+) when it is mixed with water. Common acids are recognized because they start with hydrogen. When a strong acid is mixed with water the H+ ion dissociates, leaving it separated from the rest of the molecule.

The Strength of Acids and Bases Weak acids have fewer molecules dissociate or break up and thus the number of hydrogen ions is less. The more hydrogen ions there are in the water the lower the pH value and the stronger the acid.

The pH Scale (power of Hydrogen) pH scale is used to represent how acidic or basic a solution is. The scale ranges from 0-14 with very acidic being 0, neutral being 7, and very basic being 14. Every point on the scale represents a 10 base exponent difference. Ex lemons (pH = 2.0) are 100 times more acidic than tomatoes (pH = 4.0) 7.0 is neutral (neither acidic nor basic (alkaline)). Acids range from 0-6.9 Bases range from 7.1 -14

The pH Scale (power of Hydrogen)

Neutralization Reactions (317-319)

Neutralization Reactions (317-319) What happens when an acid and a base are mixed?   When an acid and a base are mixed they react to form products that have a pH of near or at 7, this is defined as a neutralization reaction. A Neutralization reaction always produces a salt and water.

Neutralization Reactions (317-319) The products of a neutralization reaction of an acid and a base are salt and water. Acid + Base  Salt + water

Neutralization Reactions (317-319) Example: Hydrochloric acid + sodium hydroxide  sodium chloride + water HCl(aq) + NaOH(aq)  NaCl + H2O

During a Neutralization reaction, the hydrogen ion from the acid reacts with the hydroxide ion from the base to form water.   H+ + OH-  HOH = H2O

The salt from the reaction is dissolved in the water to form a salt solution which is neutral. There are many types of salts; NaCl is just one of many.

Applications: Read those on your own Antacids are examples of the use of a weak base to neutralize excess stomach acid. Antacids can be weak hydroxide bases such as magnesium hydroxide which reacts with excess stomach acid to form water and a salt. Antacids can also be bicarbonates such as sodium bicarbonate which reacts with the excess acid to form water, carbon dioxide and a salt.

Homework / MSIP Talk these ones over, you don’t have to write them out....BUT YOU HAVE TO KNOW THEM IF I ASK YOU Page 296-297 #1-4 Page 317 – 319 # 2,3,10 Write these out Page 308 – 311# 2,3,4