INDICATORS This is a substance which is one color in and acid and another color in a base. Indicators can ten be used to test for the presence of acids or bases in a substance. Some are available in paper form (litmus) and others in liquid form (methyl orange). INDICATOR | COLOR IN ACID | COLOR IN BASE | LITMUS | RED | BLUE | PHENOPTHALEIN | COLORLESS | PINK | METHYL ORANGE | RED | YELLOW | SCREENED METHYL ORANGE | RED | GREEN | BROMOTHYMOL BLUE | YELLOW | BLUE | THE pH SCALE
The strength of an acid or base is indicated by its pH. The pH scale is a number scale that indicates whether a substance is basic or acidic or neutral. * Acidic- have pH value less than 7 ( strongest acid is pH o) * Basic- have pH value of more than 7 ( strongest base is 14) * Neutral – have a pH of 7
ACIDS An acid is a substance which produces ‘free’ hydrogen ions when dissolved in water. Their properties can only be exhibited when dissolved in water. Acids are classified based on their origin, strength and basicity. Acids are proton donors.
* Clear colorless liquids * Are corrosive * Are electrolytes * They are sour * Have a low pH * React with base to produce salt and water
The word ‘acid’ is derived from the Latin word ‘acer’ which means sour.
A base is a proton acceptor. Many, but not all, are oxides and hydroxides of metals. They react with acids to form salts and water only and some are soluble in water, these are called alkalis. Alkalis are classified by their strength.
* Neutralizes acids to form salts and water * Corrosive * Have high pH * Conduct