Introduction to Acids, Bases and pH Lesson 13

Properties of Acids and Bases 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 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.  

Sour milk or tired muscles Table 1 Examples of common acids include Common name Formula Source or use Vinegar (acetic acid) HC2H3O2 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

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. 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 Turns litmus blue

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

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.

Formulas for Acids and Bases Common acids can be recognised because their formula begins with (H) hydrogen. Examples: H2SO4 H2CO3 H3PO4 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 (CO32-) or bicarbonate (HCO3-) react

The pH Scale The pH scale is used to represent how acid or basic a solution is. The scale ranges from 0-14 with very acidic being 0, neutral being 7, and very basic being 14. Every point on the scale represents a 10 base exponent difference. Ex lemons (pH = 2.0) are 100 times more acidic than tomatoes (pH = 4.0) 7.0 is neutral (neither acidic nor basic (alkaline)). Acids range from 0-6.9 Bases range from 7.1 -14

The pH Scale