Acid-Base-Know-How

= WELCOME TO THE MOST EXTREME BOWMAN AND RIPA ALLIANCE FOR LEARNING KIDS HOW TO USE ACIDS AND BASES AWESOMELY. (ONLY FOR THOSE IN AP CHEMISTRY WITH MS. BESAL)= media type="file" key="The Bowman-Ripa Allianc.wmv" I. __Bronsted-Lowry Acid-Base Models__ As according to the Bronsted-Lowry model, an acid is a substance that produces an excess of H+ ions in solution. (Proton Donor) A Base is a substance that forms excess OH- ions in solution (Proton Acceptor).- In an Acid-Base reaction a proton is transferred from an Acid to a Base. (Examples contributed by Zack Kattwinkel.)

The species formed when a proton is removed from an Acid is called the conjugate Base. The species formed when a proton is added to a Base is called the conjugate Acid. If this goes both ways, it’s called Amphiprotic. --This is very different to the Lewis approach where an acid is an electron pair acceptor and a base is an electron pair donor. An ** Arrhenius acid ** is a substance that when added to water increases the concentration of H1+ ions present.

II. __Ion Product of H20__ Water is used as a solvent in Acid-Base reactions in aqueous solutions. Water shows its amphiprotic nature as it is able to break down into H+ and OH- ions. The Eq. constant for this reaction is Kw. This is called the **ion product constant of water**. (1.0x10-14) @ 25 Celsius. When H+ is equal to OH- the solution is Neutral.

III. pH and pOH Acidity and Basicity of a solution can be described in terms of H+ and OH- concentrations. pH means "Power of the hydrogen ion" pH = -log[H+] pOH- = -log[OH-] pH + pOH = 14 The HIGHER the pH, the LESS acidic the solution is. pH < 7 Acidic pH = 7 Neutral pH > 7 Basic  Strong Acids and Bases completely dissociate in solution __Strong Acids__ - HCl HBr HI HClO4 HNO3 H2SO4 __Strong Bases__ - LiOH NaOH KOH Ca(OH)2 Sr(OH)2 Ba(OH)2 For Example: The pH of a .1 M solution of HCl is 1

pH can be measured by something called a pH meter. A less accurate but more colorful way to measure pH uses a universal indicator. pH paper is also an option.

IV. Weak Acids & Bases and Their Equilibrium Constants There are many things that can behave as a weak acid or base in that they react reversably with water to form an H+ or OH-. For instance, an anion derived from a weak acid is itself a weak base becasuse it is able to take an H+ from water leaving an OH-. Unlike strong acids and bases, weak acids and bases form an equilibrium reaction when added to water. The equilibrium constants are called Ka and Kb for acids and baes respectively. In discussing the ionization of a weak acid or base, often times we refer to the term percent ionization. This is defined as [H+]/[HB] x 100 for weak acids.

V. Acid-Base properties of Salt Solutions A salt is an ionic solid containing a cation other than H+ and an anion other than OH- or O2-. When a salt dissolves in water, the cation and anion seperate from each other. To decide whether a salt solution will be acidic, basic, or neutral, you must consider the following factors: 1. Determine the effect of the cation on the pH of water 2. Determine the effect of the anion on the pH of water 3. Consider both effects to determine the overall behavior of the salt As previously explained, some cations can act as weak acids in water solution. Also, Anions that are the conjugate bases of weak acids act themselves as weak bases. Remember that ions formed from strong acids and bases are spectator ions---, so salt solutions containing ions from weak acids and bases are also spectator ions and therefore are not weak acids and do not affect the pH of water. --Spectator Ion- An ion that serves to balance the electrical charges in a reaction environment without participating in product formation. If there is an acidic cation and a basic anion, then you must compare the Ka and kb of the respective ions to determine the overall effect. 1. if Ka is > Kb -- ACIDIC 2. if Kb is > Ka -- BASIC

VI. Buffers A BUFFER is any solution containing appreciable amounts of a weak acid and its conjugate base. Buffers are highly resistant to pH changes brought on by the addition of strong acids and bases. Buffers are widely used to maintain nearly constant pH in a variety of commercial products and lab procedures. The pH of a buffe changes clightly with the addition of small amounts of strong acids and bases. Addition of H+ converts weak base to conjugate acid. Addition of OH- converts weak acid to conjugate base. In both of these cases, H+ ion concentration changes and thus the pH changes very slightly. A buffer has a limited capacity of how much H+ or OH- it can except without drastically changing the pH.

Buffer problems:

[] (contributed by Taylor Parr)

Sample problem contributed by Lauren Wilhoit.

VII. Indicators and Titrations

This is Number 44 on page 398! This is the CORRECT way to do it!

An acid-base INDICATOR is used in determining the equivalence point of an acid base TITRATION. (The point at which the reaction is complete) The time when the INDICATOR changes color coincides with the equivalence point.

There are different types of indicators that can include litmus paper, methyl orange, phenolphthalein, and bromothylmol blue, among others. When hydroxide ions react with the litmus paper, it turns blue, and when hydrogen ions react with it it turns red. If the reaction taking place between the litmus paper and the ions in solution are at equilibrium, the paper turns purple. Methyl orange is used in the titration of weak bases and strong acids. It changes from red at pH 3.1 to orange yellow at pH 4.4. Phenolphthalein is colorless at pH 8.3 and a deep red at pH 9.8. Bromothylmol blue is yellow at pH 6.0 and blue at pH 7.6. (added by Courtney S.)

The equation: __ [HIn] __ [In-] From this expression, the color of the indicator depends on the H+ or the pH of the solution. Also this depends on the Ka of the indicator.

from Catherine  