Acids have a low pH below 7 and turn litmus paper red, while bases have a high pH above 7 and turn litmus paper blue. Common acids include hydrochloric acid, sulfuric acid, and nitric acid found in stomach acid and some cleaners. Bases like bleach and those in toothpaste are often used to clean around the home. Water is neutral with a pH of 7, while indicators like litmus paper and universal indicator can test if a substance is an acid or base by changing color.