Welcome to our lesson on acids, bases, and salts! Let's start with acids. Acids are substances that produce hydrogen ions, written as H plus, when dissolved in water. They have several distinctive properties: they taste sour like lemon juice, turn blue litmus paper red, have a pH less than 7, conduct electricity when dissolved in water, and are corrosive. Common examples include hydrochloric acid, sulfuric acid, and nitric acid. The diagram shows an acid solution with hydrogen ions and how it affects litmus paper and the pH scale.
Now let's learn about bases and alkalis. Bases are substances that react with acids. Alkalis are a special type of base that are soluble in water and produce hydroxide ions, written as OH minus. Alkalis have distinctive properties: they taste bitter, feel soapy to touch, turn red litmus paper blue, have a pH greater than 7, and conduct electricity when dissolved in water. Common examples include sodium hydroxide, potassium hydroxide, and calcium hydroxide. The diagram shows an alkali solution with hydroxide ions and how it affects litmus paper and appears on the alkaline side of the pH scale.
The pH scale is a crucial tool in chemistry that measures how acidic or alkaline a substance is. It ranges from 0 to 14. Values less than 7 are acidic, exactly 7 is neutral like pure water, and values greater than 7 are alkaline. We use indicators to determine pH. Litmus paper is simple: it turns red in acids and blue in alkalis. Universal indicator is more sophisticated, showing a range of colors from red for strong acids through green for neutral to purple for strong alkalis. These indicators help us quickly identify whether a substance is acidic or alkaline.
Now let's explore neutralization reactions. Neutralization is the reaction between an acid and a base or alkali. The general equation is: Acid plus Base gives Salt plus Water. For example, hydrochloric acid reacts with sodium hydroxide to produce sodium chloride salt and water. During this reaction, the hydrogen ions from the acid react with the hydroxide ions from the alkali to form water molecules. The remaining ions combine to form a salt. The result is that the pH moves towards 7, becoming more neutral.
Finally, let's learn about salts and other acid reactions. Salts are ionic compounds formed when the hydrogen ion in an acid is replaced by a metal ion or ammonium ion. Salt names come from the acid used: hydrochloric acid gives chlorides, sulfuric acid gives sulfates, and nitric acid gives nitrates. Besides neutralization, acids have other important reactions. They react with metals to produce salts and hydrogen gas, and with carbonates to produce salts, water, and carbon dioxide gas. These reactions are fundamental in chemistry and have many practical applications.