Acids Tastes sour Reacts with metals and carbonates - Corrosive  wear away metals Turns blue litmus red H+ ions in water

Examples of Acids HCl (Hydrochloric Acid) HNO3 (Nitric Acid) H2SO4 (Sulfuric Acid) H2CO3 (Carbonic Acid) HC2H3O2 (Acetic Acid) H3PO4 (Phosphoric Acid)

Common Acids Oranges, lemons Folic Acid (Green, leafy vegetables) Lactic Acid (builds up in muscles) Car batteries (sulfuric acid) Fertilizers (Nitric and phosphoric acids)

Bases Tastes bitter Feels slippery Turns red litmus paper blue “Opposite of Acids” OH- Ions in water

Examples of Bases NaOH (Sodium hydroxide) KOH (Potassium hydroxide) Ca(OH)2 (Calcium hydroxide) Mg(OH)2 (Magnesium hydroxide) Al(OH)3 (Aluminum hydroxide) NH3 (Ammonia)

Common Bases Baking soda (reacts with acids to produce CO2 gas) Milk of Magnesia and Calcium Carbonate Cement Drain cleaners and glass cleaner (ammonia)

Review How can you use litmus paper or universal indicator to tell the difference between an acid and a base? How can you tell if a food may contain an acid or a base as one of its ingredients? Acids=sour taste and Bases=bitter taste

Review (cont.) Name at least two ways that acids and bases are useful around your home. Acids=foods and household cleaners Bases=unclog drains, clean windows, or cause breads and biscuits to rise

pH Scale A range of values from 0 to 14 Expresses the concentration of hydrogen ions in a solution Low pH = concentration of H+ is high High pH = concentration of H+ is low

pH (cont.) pH less than 7 the solution is acidic pH more than 7 the solution is basic

pH Examples Hydrochloric Acid = pH = 0 Lemon = pH = 2 Banana = pH = about 4.8 Water = pH = 7 = neutral Blood = pH = 7.5 Soap = pH = 10 Drain Cleaner = pH = 14

STOP HERE IF you are in 8 th Grade

WATER Let’s refer to page 1 of Notes II. H 2 O (l) + H 2 O (l) ↔ H 3 O + (aq) + OH - (aq) For now, we can write this simply as: H 2 O (l) ↔ H + (aq) + OH - (aq)

Some important facts to remember about the acid- base nature of water: The molar concentration of hydrogen ions, [H + ], and the molar concentration of hydroxide ions, [OH - ], are equal to each other, i.e., [H + ] = [OH - ], in pure water at 25 o C. In pure water at 25 o C, [H + ] = 1 x M and [OH - ] = 1 x M. In any aqueous solution (not just pure water), the balance (equilibrium) between both sides of equation (1) can be expressed by the arithmetic product of the concentrations, [H + ] times [OH - ] = 1 x [H + ] x [OH - ] = Or… [H + ] = ÷ [OH - ]Or… [OH - ] = ÷ [H + ]

pH There are many ways to consider acids and bases. One of these is pH. [H + ] is critical in many chemical reactions. A quick method of denoting [H + ] is via pH. By definition pH = – log [H + ], [H + ] = 10 -pH The pH scale, similar to the Richter scale, describes a wide range of values An earthquake of “6” is 10  as violent as a “5” Thus, the pH scale condenses possible values of [H + ] to a 14 point scale Also, it is easier to say pH = 7 vs. [H + ] = 1 x 10 –7

Modern Theory of Acids and Bases An acid is a hydrogen ion (H + ) donor in a chemical reaction A base is a hydrogen ion (H + ) acceptor in a chemical reaction So what does this mean? First of all, it means that there really are no free H + ions in solution – the H + ions are actually transferred from the acid to the base in the solution. It’s all about chemical substances ACTING AS ACID (donating H + ) reacting with something ACTING AS BASE (accepting H + ).

Examples Example 1:H 2 O (acts as acid) donates an H + ion to another H 2 O (acts as base) (water is a “very weak” acid or base, so hardly any H + is transferred) H 2 O (l) + H 2 O (l)  OH - (aq) + H 3 O + (aq) Example 2:Hydrogen chloride (HCl) acts as acid in water. HCl donates H + to H 2 O (acts as base) to form hydronium ion and chloride ion. (HCl is a “strong” acid, so ALL of its H + is transferred) HCl (aq) + H 2 O (l)  H 3 O + (aq) + Cl – (aq) Example 3: Ammonia (NH 3 ) acts as base in water. NH 3 accepts H + from water (acts as acid) to form ammonium ion and hydroxide ion. (NH 3 is a “weak” base and only some of the NH 3 accepts H + ) NH 3 (aq) + H 2 O (l)  NH 4 + (aq) + OH - (aq)

In general If you add an acid to water, H 3 O + is formed, and [H 3 O + ] = 10 -pH. If you add a base to water, OH - is formed, and [OH - ] = 10 (pH-14) {Wow!} If you mix an acid with a base, then H + ions of the acid are transferred to the base. Any left over acid forms H 3 O + or left over base forms OH -. In either case, the pH is determined as above.

Acid-Base Reactions When acids and bases react the results in the product being neutral (or close to neutral) This is called a neutralization Produces water and a salt Ex. HNO3 + KOH  H2O + KNO3 (water and potassium nitrate)

Salts A salt is any ionic compound that that can form from the neutralization of an acid with a base

Review If the pH of a solution is 6, would you expect more or fewer hydrogen ions (H+) than in a solution with a pH of 3? Explain why. Fewer. The lower the pH, the higher the concentration of hydrogen ions.

Review (cont.) What does the term salt mean to a chemist, and how may a salt form? An ionic compound that forms from the neutralization of an acid with a base. What salt would form from a reaction between HCl and Ca(OH)2? CaCl2 (calcium chloride)