Acids and Bases (P293-295) Lesson 12 September 14th, 2010

Acids and Bases (P293-295) 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.

When Acids are dissolved in water they release H+ . Ex HCl(aq)  H+(aq) + Cl-(aq)

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 Turn blue litmus red

Identifying Acids You can identify an acid from its name or from its chemical formula. Usually, the name of an acid ends with the word “acid.” If you are given the chemical formula of a substance, you know that it is an acid if: the chemical formula starts with H (the symbol for a hydrogen atom) OR the chemical formula ends with COOH (the formula for a carboxyl polyatomic ion) Example – HF(aq)­ hydrofluoric acid, CH3COOH­ (aq) acetic acid.

Naming Acids There are two rules for naming acids when the chemical formula of an acid starts with H and has only one other non-metallic element Step Examples HCl (aq) HF (aq) Start with the Prefix “hydro” hydro Hydro 2.To the first part of the name of the non-metallic element, add the suffix “ic” and add the word “acid” Hydrochloric acid Hydrofluoric acid

Naming Acids (with polyatomic ions) Some acids contain a polyatomic ion. When the polyatomic ion in an acid contains an oxygen atom (O) and its name ends in “ate”, the acid can be named by the steps shown below. Step Examples H2SO4(aq) H3PO4(aq) Start with the name of the element in the polyatomic ion that is not oxygen sulphur phosphorus 2.Add the suffix “ic” and the word “acid” sulphuric acid phosphorusic acid

Sour milk or tired muscles Table 1 Examples of common acids include Common acids Common name Formula Source or use Vinegar (acetic acid) HC2H3O2 or HC2H2OOH Salad dressing Citric acid HC6H7O7 Oranges, lemons Ascorbic acid HC6H7O6 Vitamin C Lactic acid HC­3H5O3 Sour milk or tired muscles Sulfuric acid H2SO4 Car batteries

Acids are widely used in industry, they are used in many manufacturing processes including; fertilizers, explosives, refining oil, and electroplating materials.   Acids that that react with metals and glass are described as being Corrosive. These acids can be dangerous to humans and the environment.

Base  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.

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

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 Turn Red litmus blue

Identifying and Naming Bases A base can also be identified from its name or its chemical formula. A substance is a base if its name begins with the name of a metallic ion and ends with the word “hydroxide.” A substance is also a base if: the chemical formula starts with a metallic ion or with the ammonium ion NH4+ AND the chemical formula ends with OH (called a hydroxyl group)

Naming Bases The name of a base can be determined from its chemical formula by following the steps shown in Table 5.5. Notice that all bases (in this class) are followed by the word “hydroxide.”

Naming Bases Step Examples KOH (aq) NH4OH (aq) Write the name of the positively charged metallic ion that is at the beginning of the chemical formula. This step remains the same if the positively charged ion is a polyatomic ion. Potassium Ammonium Add the word “hydroxide” Potassium hydroxide Ammonium hydroxide

Table 2 Examples of some common bases Common Name Formula Source or use Sodium hydroxide NaOH Drain cleaner Potassium hydroxide KOH Soap, cosmetics Aluminum hydroxide Al(OH)­3 Antacids Ammonium hydroxide NH­­4OH Window cleaner. Sodium bicarbonate NaHCO3 Baking soda, used in baking Potassium sulphite K2SO3 Food preservative

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

Where do Acids and Bases come from? 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.

Reactions of Metals 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 + O2  2MgO MgO + H2O  Mg(OH)2

Reactions of Nonmetals 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 S8 + 8O2 8SO2 SO2 + H2O  H2SO3

Homework /msip Read pages 293 – 295 # 2,3,4,6