1 The Chemistry of Acids and Bases Chapter 19

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3 Acid and Bases

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6 Acids Have a sour taste. Vinegar is a solution of acetic acid. Citrus fruits contain citric acid. React with certain metals to produce hydrogen gas. React with carbonates and bicarbonates to produce carbon dioxide gas Have a bitter taste. Feel slippery. Many soaps contain bases. Bases

7 Some Properties of Acids þ Produce H + (as H 3 O + ) ions in water (the hydronium ion is a hydrogen ion attached to a water molecule) þ Taste sour þ Corrode metals þ Electrolytes þ React with bases to form a salt and water þ pH is less than 7 þ Turns blue litmus paper to red “Blue to Red A-CID”

8 Common acids Sulfuric acid: battery acid Stomach acid: hydrochloric acid Vinegar: acetic acid Sodas: phosphoric acid Explosives: nitric acid Lemons and limes: citric acid

9 Acid Nomenclature Flowchart

10 Some Properties of Bases ☑ Produce OH - ions in water ☑ Taste bitter, chalky ☑ Are electrolytes ☑ Feel soapy, slippery ☑ React with acids to form salts and water ☑ pH greater than 7 ☑ Turns red litmus paper to blue “Basic Blue”

11 Some Common Bases NaOHsodium hydroxidelye KOHpotassium hydroxideliquid soap Mg(OH) 2 magnesium hydroxide“MOM” Milk of magnesia Al(OH) 3 aluminum hydroxideMaalox (antacid)

12 Acid Strength The strength of an acid refers to its tendency to lose a proton (H + ).acidproton A strong acid is one that completely ionizes (dissociates) in an aqueous solution.dissociates

13 A weak acid only partially dissociates in water. Ex: carbonic acid (H 2 CO 3 ) and acetic acid (CH 3 COOH).carbonic acidacetic acid

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15 A strong base is a basic chemical compound that can remove a proton (H + ) from (or deprotonate) a molecule of a very weak acid in an acid-base reaction.deprotonate

16 Strong bases are strong electrolytes. Strong bases ionize completely in water and produce a large number of hydroxide ions. Weak bases are weak electrolytes, which only ionize to a small amount in water.

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18 The pH scale is a way of expressing the strength of acids and bases. Instead of using very small numbers, we just use the NEGATIVE power of 10 on the Molarity of the H + (or OH - ) ion. Under 7 = acid 7 = neutral Over 7 = base

19 pH of Common Substances

20 Calculating the pH pH = - log [H+] (The [ ] mean Molarity, or concentration) Example: If [H + ] = 1 X pH = - log 1 X pH = - (- 10) pH = 10 Example: If [H + ] = 1.8 X pH = - log 1.8 X pH = - (- 4.74) pH = 4.74

21 Try These! Find the pH of these: 1) A 0.15 M solution of Hydrochloric acid 2) A 3.00 X M solution of Nitric acid

22 More About Water H 2 O can function as both an ACID and a BASE. In pure water there can be AUTOIONIZATION

23 pOH Since acids and bases are opposites, pH and pOH are opposites! pOH does not really exist, but it is useful for changing bases to pH. pOH looks at the perspective of a base pOH = - log [OH - ] Since pH and pOH are on opposite ends, pH + pOH = 14

24 pH[H + ][OH - ]pOH

25 pH testing There are several ways to test pH –Blue litmus paper (red = acid) –Red litmus paper (blue = basic) –pH paper (multi-colored) –pH meter (7 is neutral, 7 base) –Universal indicator (multi-colored) –Indicators like phenolphthalein –Natural indicators like red cabbage, radishes

26 Paper testing Paper tests like litmus paper and pH paper –Put a stirring rod into the solution and stir. –Take the stirring rod out, and place a drop of the solution from the end of the stirring rod onto a piece of the paper –Read and record the color change. Note what the color indicates. –You should only use a small portion of the paper. You can use one piece of paper for several tests.

27 pH paper

28 pH meter Tests the voltage of the electrolyte Converts the voltage to pH Very cheap, accurate Must be calibrated with buffer solutions with known pH values

29 pH indicators Indicators are dyes that can be added that will change color in the presence of an acid or base. Some indicators only work in a specific range of pH Once the drops are added, the sample is ruined Some dyes are natural, like radish skin or red cabbage

30 ACID-BASE REACTIONS If you were to mix a strong acid and strong base of the same concentration, a neutral solution will result. This is called a neutralization reaction. Similar reactions with weak acids or bases will not result in a neutral solution In general, a reaction an an acid with a base produces water and a type of compound known as salts. Salt: anion from acid & cation from base HCl (aq) + NaOH (l) → NaCl (aq) + H 2 O (l)

31 ACID-BASE REACTIONS One way neutralization reactions are used is in a process called titration. This allows scientists to determine unknown concentrations of acids or bases through calculations When the [acid]=[base], an equivalence point is reached (moles H + =moles OH - )

32 Setup for titrating an acid with a base

33 Titration 1. Add solution from the buret. 2. Reagent (base) reacts with compound (acid) in solution in the flask. 3.Indicator shows when exact stoichiometric reaction has occurred. (Acid = Base) This is called NEUTRALIZATION.

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