Terms Acid Base Indicator Titration pH pOH

Reactions, Acids and Bases Chapters 17 & 19

Definitions Acid: Substance that, when dissolved in water, increases the concentration of hydrogen ions. Base: Substance that, when dissolved in water, increases the concentration of hydroxide ions. 3

Definitions Brønsted–Lowry Acid: Proton donor Base: Proton acceptor 4

Conjugate Acids and Bases: Reactions between acids and bases always yield their conjugate bases and acids. 5

Conjugate Acids and Bases: Bases react with water to produce hydroxide ion. 6

Acid and Base Strength Strong acids/bases are completely dissociated in water. Their conjugate bases/acids are relatively weak. Weak acids/bases only dissociate partially in water. Their conjugate bases/acids are relatively strong. 7

Acid = higher [H+] than water, & pH < 7 In pure water, pH = 7.00 Acid = higher [H+] than water, & pH < 7 Base = lower [H+] than water, & pH >7. 8

pH pH = −log [H+] pH expresses the acidity of a solution pOH expresses the basicity of a solution pOH = -log [OH-] NOTE: that pH + pOH = 14.00 Therefore if you calculate one you can determine the other. 9

Calculating [H+] Since the pH = -log [H+] In order to calculate the [H+] you must take the antilog: [H+] = antilog (-pH) [H+] = 10-pH

Titration Is a method for determining the concentration of a solution by reacting a known volume and concentration of a solution with the unknown solution.

Indicator Red cabbage contains a molecule called flavin. The color of the juice changes in response to changes in its hydrogen ion concentration. Acids will donate hydrogen ions in a solution and have a low pH (pH < 7). Bases accept hydrogen ions and have a high pH (pH > 7). Very acidic solutions will turn flavin a red color. Neutral solutions result in a purplish color. Basic solutions appear in greenish-yellow. Therefore, it is possible to determine the pH of a solution based on the color it turns the flavin in red cabbage juice.

Group Activity Get with your lab partners Create some sort of demonstration for the class that explains…. Factors affecting Reaction Rates: 17.2 page 536 It must include the Nature of Reactants, Concentration, Surface Area, Temperature and Catalysts. You must clearly state each topic and give clear explanations to receive full credit. This will count as a lab grade.

Challenge It’s 1700 You have an unknown substance Want to know if it’s acidic or basic You have 4 known substances to compare However, you need some sort of indicator to tell you which if it is acidic or basic What do you do??? Go to nature… find plants, dissolve your substances in them and observe there color!!!

Phenolphthalein An acid-base indicator is an organic compound whose color is sensitive to changes in pH. The acid form of the indicator contains an acidic hydrogen while the base form does not. It is the presence (or absence) of this hydrogen atom that determines the color of the indicator. Phenolphthalein, a common indicator in the chemistry lab, is colorless under acidic conditions and bright pink (magenta) under basic conditions. The structures of the acidic and basic forms of the molecule are shown below: Phenolphthalein – Acidic Form (Colorless) Phenolphthalein – Basic Form (Magenta)

Indicators Anthocyanin dyes, the organic molecules that give cabbage its colors, can be used in the chemistry lab as acid-base indicators. The purpose of this lab is to prepare a homemade indicator using the cabbage.

pH = -log [H+] pOH = -log [OH-] [H+] = 10 ^ -pH [OH-] = 10 ^ -pOH M=mol / L M1V1 = M2V2 pH + pOH = 14 pH = -log [H+] pOH = -log [OH-] [H+] = 10 ^ -pH [OH-] = 10 ^ -pOH

Practice time!!! Get out your textbooks and do Practice Problems Practice Problem 19 (pg 611) Practice Problem 20 (pg 612) Practice Problem 21 (pg 614) Practice Problem 22 (pg 614)