In acid-base chemistry, salts are ionic compounds that result from the neutralization reaction of an acid and a base. Basic salts contain the conjugate base of a weak acid, so when they dissolve in water, they react with water to yield a solution with pH greater than 7.0. An acid is defined as a substance whose water solution tastes sour, turns blue litmus red and neutralizes bases. A substance is called base if its aqueous solution tastes bitter, turns red litmus blue or neutralizes acids. Salt is a neutral substance whose aqueous solution does not affect litmus. Common examples include hydrochloric acid, sulfuric acid, citric acid and ethanoic acid (vinegar/acetic acid). Bases are a group of substances that neutralize acids. Soluble bases are called alkalis. Salts are odourless and have a salty taste, and many are soluble in water. Acids react with active metals to give salt and hydrogen gas. Acids react with metal carbonates and metal hydrogen carbonates to give salt, water and carbon dioxide. Acids react with bases to give salt and water. Acids react with metal oxides to give salt and water.