Lesson 14

 Acids are traditionally considered any chemical compound that, when dissolved in water, gives a solution with a hydrogen ion activity greater than in pure water, i.e. a pH less than 7.0. They also:  Taste sour  Are good conductors of electricity (they release H + ions when they are in water)  React with compounds that contain carbonate  Are generally quite reactive  Inflict a sharp burning pain when handled  Turns litmus red

 When Acids are dissolved in water they release H +  Ex HCl (aq)  H + (aq) + Cl - (aq)  Acids are widely used in industry, they are used in many manufacturing processes including; fertilizers, explosives, refining oil, and electroplating materials.

 Table 1 Examples of common acids include Common nameFormulaSource or use Vinegar (acetic acid)HC 2 H 3 O 2 Salad dressing Citric acidHC 6 H 7 O 7 Oranges, lemons Ascorbic acidHC 6 H 7 O 6 Vitamin C Lactic acidHC­ 3 H 5 O 3 Sour milk or tired muscles Sulfuric acidH 2 SO 4 Car batteries

 Acids that that react with metals and glass are described as being Corrosive. These acids can be dangerous to humans and the environment.

 A base is most commonly thought of as an aqueous substance that can accept hydrogen ions.  bases can commonly be thought of as any chemical compound that, when dissolved in water, gives a solution with a hydrogen ion activity lower than that of pure water, i.e. a pH higher than 7.0 at standard conditions.

 They also:  Taste bitter  Are good conductors of electricity (They release OH - ions when dissolved in water)  Break down proteins into smaller molecules  May also be called alkaline  Feel slippery when handled  Turns litmus blue

When bases are released in water they release OH - ions Example  NaOH (aq)­  Na + (aq) + OH - (aq)

Common NameFormulaSource or use Sodium hydroxideNaOHDrain cleaner Potassium hydroxideKOHSoap, cosmetics Aluminum hydroxideAl(OH) 3 Antacids Ammonium hydroxideNH 4 OHWindow cleaner. Sodium bicarbonateNaHCO 3 Baking soda, used in baking Potassium sulphiteK 2 SO 3 Food preservative

 Bases that feel slippery to the touch are Corrosive and should be handled carefully with gloves and eye protection.

 Acids and bases do not exist in nature as raw materials  Raw materials – materials from the earth that can be used to make new products  Acids and bases are formed when certain elements react with oxygen to form oxides.

 Metals tend to lose electrons and react with oxygen to form solid metal oxides. When these oxides are mixed with water they react and form bases, many of these bases are very strong when concentrated. Example  2Mg + O 2  2MgO  MgO + H 2 O  Mg(OH) 2

 Generally elements from the groups VA, VIA, and VIIA need electrons to complete their valence and are called nonmetals. Nonmetals react with oxygen to form nonmetal oxides which are normally gases. These oxides then form acids when mixed with water. Example  S 8 + 8O 2  8SO 2­  SO 2 + H 2 O  H 2 SO 3

Acids  Common acids can be recognised because their formula begins with (H) hydrogen.  Examples: H 2 SO 4 H 2 CO 3 H 3 PO 4 HCl

Bases  Bases are not as easy to recognise, most will contain a hydroxyl group (OH - ).  Ex: NaOH, Mg(OH) 2 Other compounds can form bases when they react with water to form OH - ions. Compounds that contain carbonate (CO 3 2- ) or bicarbonate (HCO 3 - ) react

 When an acid and a base are mixed they react to form products that have a pH of near or at 7, this is defined as a neutralization reaction. A Neutralization reaction always produces a salt and water. Acid + Base  Salt + water 

Example:  Hydrochloric acid + sodium hydroxide  sodium chloride + water  HCl (aq) + NaOH (aq)  NaCl + H 2 O 

 During a Neutralization reaction, the hydrogen ion from the acid reacts with the hydroxide ion from the base to form water.   H + + OH -  HOH = H 2 O  The salt from the reaction is dissolved in the water to form a salt solution which is neutral.  There are many types of salts; NaCl is just one of many.

First-Aid Treatments Use Neutralization:  The interpretation of "Danger" and First-Aid labels on household cleaners provides an exercise in the use of acid-base principles.

 Example:  A toilet bowl cleaner - Danger: Corrosive - produces chemical burns. Contains Hydrochloric Acid. Do not get in eyes, on skin. May be fatal if swallowed. Do not breath vapor or fumes. First-Aid:  Internal - Call physician. Drink a teaspoon of magnesia, chalk, small pieces of soap, raw egg white, or milk.

External  Eyes - Wash with water for 15 minutes.  Skin - Wipe acid off gently, flood with water, cover with moist magnesia or baking soda.   Solution: The First-Aid consists of either diluting the acid, coating the stomach lining, or neutralizing it.  Mg(OH) 2 + HCl --> MgCl 2 + HOH magnesia

 Antacids are examples of the use of a weak base to neutralize excess stomach acid. Antacids can be weak hydroxide bases such as magnesium hydroxide which reacts with excess stomach acid to form water and a salt. Antacids can also be bicarbonates such as sodium bicarbonate which reacts with the excess acid to form water, carbon dioxide and a salt.

Hand in when done