Unit 9: Acid/Base Chemistry Chemistry CPA 2014

Demo – Rainbow in a Cylinder What do you think? What causes a color change? What is an acid? Give examples. What is a base? Give examples. Do they mix together or react with one another? http://www.elmhurst.edu/~chm/demos/RainbowCylinder2.htm

Examples of every acids and bases Lemons Orange Juice Vinegar Car batteries Stomach Acid Soft drinks Vitamin C Asprin Bases: Mustards Antacids (TUMS) Drain-o Soap Detergents Fertilizers Lawn lime Baking soda Coffee

More Everyday Acids and Bases

Acids Acids - react with certain metals have a sour taste are caustic, i.e. they "eat through" many materials turn indicators certain distinctive colors. e.g., turn litmus red. Conduct electricity

Bases Bases react with certain other metals have a bitter taste are also caustic turn indicators other distinctive colors. e.g., turn litmus blue. Conduct electricity

Measuring Acid & Base levels Indicators Turn a certain color according to the amount of hydrogen ions (H+) or hydroxide ions (OH-) pH A scale used to quantify the strength of an acid or base.

Defining Acids – Atomic Style! An acid is a substance that produces hydronium ions in water. A hydronium ion consists of a hydrogen ion attached to a water molecule: Hydronium = H3O+

Defining Bases – Atomic Style! A base is a substance that produces hydroxide ions (OH-) when it dissolves in water.

pH A quantitative measure to express the concentration of hydronium ions [H+] in a solution. pH means “power of hydrogen”

The pH Scale – in pictures!

pH Scale Low pH (0-7) High pH (7-14) pH of 7 high amount of H+ Low amount of OH- acid High pH (7-14) small amount of H+ High amount of OH- base pH of 7 Equal amounts of H+ and OH- neutral

pH Scale in more color…

Formulas – pH pH = -log [H+] Note: Molarity is commonly abbreviated by using square brackets, thus [H+] = hydrogen ion concentration

Problem #1 Calculate the pH if the [H+] = 1 x 10-4 M pH = -log [H+] pH = -log [1x10-4] pH = 4 acidic

Formulas - pOH Power of hydroxide ion pOH = - log [OH-]

Problem #2 Calculate the pOH if the [OH-] = 1x10-2 pOH = - log[1x10-2]

Relationship between pH and pOH pH + pOH = 14 So if the pOH is 2, then the pH is 12 and basic Always use pH to determine if the solution is acidic or basic

Practice Assignment [H+] pH [OH-] pOH Acidic or Basic 1 1 x 10-5 5 9 Acidic 2 7 3 1 x 10-4 4 1 x 10-2 11

Strength vs. Concentration The strength of an acid is related to the proportion of which it has reacted with water to produce ions. Strong acid/base means it separates into ions in solution very easily. Weak acid/base means it doesn’t separate into ions in solution as much. The concentration tells you about how much of the original acid/base is dissolved in the solution.

Strong vs. Weak Notice how strength means separation (how much they split), not concentration (how many there are)

Buffers A buffer resists change to pH when a small amount of acid or base is added to a solution. Can be used in a pool or a lake Your body has natural buffers to maintain the pH of certain organs

Strong Example: HCl  H+ + Cl- Buffers are made of… A weak acid and its salt H2PO4- ↔ H+ + HPO4-2 A weak base and its salt NH3 + HOH ↔ NH4+ + OH- Remember strength is determined by its ability to dissociate (into ions) in solution Strong Example: HCl  H+ + Cl-

Neutralization Reaction A reaction between an acid and a base The products are always a salt and water Acid + Base  a Salt + Water A salt is the substance formed when the cation of the base combines with the anion of the acid. These substances generally have a neutral pH. http://education-portal.com/academy/lesson/weak-acids-weak-bases-and-buffers.html http://www.youtube.com/watch?v=l9dliAngF2k

Example HCl + NaOH  NaCl + HOH acid + base  sodium chloride (a salt) + water 2HCl + Mg(OH)2  MgCl2 + 2HOH stomach acid + base  neutral products Demo: Upset Tummy? MOM to the Rescue!

Neutralization Reaction Practice Problems For each of the following reactants, predict the products: H2CO3 and Sr(OH)2 __________ + H2O HClO4 and NaOH  _________ + _________ HBr and Ba(OH)2 _________ + __________

Predict the Acid and the Base from the Salt. For each of the following salts, tell which acid and based formed it. Predict the Acid and the Base from the Salt. Salt Acid Base Zn(NO3)2   Al(ClO)3 NaCl Ca3(PO4)2 (NH4)2C2O­4

Acid Rain environmental problem affects large parts of the US and Canada damaging to lakes, streams, and forests and the plants and animals that live in these ecosystems.

Effects of Acid Rain Damage to plants Damage to animals Damage to buildings

Effects of Acid Rain on Marble (marble is calcium carbonate) George Washington: BEFORE acid rain George Washington: AFTER acid rain

Acid rain affects the whole world – no part of the world is safe. Where is Acid Rain? Acid rain affects the whole world – no part of the world is safe.

Causes of Acid Rain Natural Sources: Man-Made Sources: volcanoes decaying vegetation Forest fires lightning Man-Made Sources: emissions of sulfur dioxide (SO2) Emissions of nitrogen oxides (NOx)

In the United States, roughly 2/3 of all SO2 and 1/4 of all NOx come from electric power generation that relies on burning fossil fuels, like coal.  Acid rain occurs when these gases react in the atmosphere with water, oxygen, and other chemicals to form various acidic compounds. The result is a mild solution of sulfuric acid and nitric acid.

wet deposited material dry deposited material 2 Types of Acid Rain wet deposited material dry deposited material

Wet Deposition acidic rain, fog, and snow If the acid chemicals in the air are blown into areas where the weather is wet, the acids can fall to the ground in the form of rain, snow, fog, or mist. The strength of the effects depends on several factors: how acidic the water is the chemistry of the soils involved the types of fish, trees, and other living things that rely on the water.

Dry Deposition In areas where the weather is dry, the acid chemicals may become incorporated into dust or smoke and fall to the ground sticking to the ground, buildings, homes, cars, and trees. Dry deposited gases and particles can be washed from these surfaces by rainstorms, leading to increased runoff. This runoff water makes the resulting mixture more acidic. About half of the acidity in the atmosphere falls back to earth through dry deposition.

Measuring Acid Rain Normal rain is slightly acidic because carbon dioxide (CO2) dissolves into it forming weak carbonic acid, giving the resulting mixture a pH of approximately 5.6 at typical atmospheric concentrations of CO2. As of 2000, the most acidic rain falling in the U.S. has a pH of about 4.3.

Reducing Acid Rain Societal changes Individual action Use Alternative Energy Sources Restore a Damaged environment Individual action Turn off lights, computers, and other appliances when you're not using them. Use energy-efficient appliances Keep your thermostat at 68°F in the winter and 72°F in the summer. Insulate your home as best you can. Carpool, use public transportation, or better yet, walk or bicycle whenever possible Buy vehicles with low NOx emissions, and properly maintain your vehicle.

Clean Air Act Amendments – 1990 imposes emission restrictions on fossil fueled power plants

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