Acids and Bases

• Acids, bases, and salts are important chemical compounds.

Acids

• Acids in pure form consist of covalent molecules but form ions in water.
• Acids in solutions are described as acidic
• Acids can be defined in three ways:

Acids Defined

• Acid contains hydrogen replaceable by a metal to form a salt.
• Example: Zinc reacts with hydrochloric acid to form zinc chloride and hydrogen gas.
• Acid forms hydroxonium ions when dissolved in water.
• When acid dissolves in water, it forms hydrogen ions which associate with water molecules to form hydroxonium ions.
• Acid is a proton donor.
• Hydrogen atom loses an electron to become a proton.
• Acids donate protons to other substances.
• Example: Acid donates hydrogen ions to water molecules.

General Properties of Aqueous Acids

• Acids' properties in pure form differ from their aqueous solutions.
• H+ ions present in water cause acidic properties.
  • Acids have a sour taste.
  • Acids are corrosive.
  • Acids turn litmus from blue to red.
  • Acids conduct electricity and are electrolytes.
• Acids react with bases to form a salt and water.
• This reaction is called a neutralization reaction.
• Acids react with carbonates or hydrogencarbonates to form a salt, water, and carbon dioxide.
• Acids react with reactive metals to form a salt and hydrogen (except nitric acid).
• Nitric acid releases nitrogen oxides instead of hydrogen.

Basicity (Proticity) of Acids

• The basicity of an acid refers to the number of moles of H+ ions produced per mole of acid.
  • Monobasic acids produce one mole of H+ ions (e.g., hydrochloric acid).
  • Monobasic acids form normal salts only.
  • Dibasic acids produce two moles of H+ ions (e.g., sulfuric acid).
  • Dibasic acids can form normal and acid salts.
  • Tribasic acids produce three moles of H+ ions (e.g., phosphoric acid).
  • Tribasic acids can form normal and acid salts.

Acid Anhydrides

• Acid anhydride is an acidic oxide of a non-metal that reacts with water to form an acid.
• Carbon dioxide reacts with water to form carbonic acid.
• Sulfur dioxide reacts with water to form sulfurous acid.
• Sulfur trioxide reacts with water to form sulfuric acid.

Acids in Daily Life

• Antacids contain sodium hydrogencarbonate and citric or tartaric acid to neutralize stomach acid.
• Carbon dioxide is produced, causing fizz and improving taste.
• Baking powder contains tartaric acid and sodium hydrogencarbonate; heat releases carbon dioxide, causing cakes to rise.
• Fire extinguishers contain carbon dioxide under pressure.
• Carbon dioxide is non-flammable and smothers fire due to its high density.

Bases

• Base is chemically opposite to an acid.
• Base reacts with an acid to form salt and water.
• Base is a proton (H+ ion) acceptor.
• Metal hydroxides accept hydrogen ions from acids to form water.
• Bases include ammonia and metal oxides and hydroxides.

Alkalis

• Alkali dissolves in water to form a solution containing OH- ions.
• Alkali solution is described as alkaline.
• Example: Sodium hydroxide dissolves in water to form sodium and hydroxide ions.
• Most bases are insoluble and not alkalis.

General Properties of Aqueous Alkalis

• Alkalis have a bitter taste.
• Alkalis are soapy to touch.
• Alkalis are corrosive.
• Alkalis turn litmus from red to blue.
• Alkalis conduct electricity and are electrolytes.
• Alkalis react with solutions containing metal ions (except potassium and sodium) to form insoluble precipitates.
• Alkalis react with zinc and aluminum to form a salt and hydrogen.
• Alkalis react with ammonium salts to form a salt, water, and ammonia.
• All bases react with acids to form salt and water.

Recognizing Acids and Alkalis

• Acids and alkalis can be recognized using indicators.
• Indicator shows one color in acidic solution and a different color in alkaline solution.
  • Litmus: red in acid, blue in alkali.
  • Phenolphthalein: colorless in acid, pink in alkali.
  • Methyl orange: pink/red in acid, yellow in alkali.
  • Screened methyl orange: red in acid, yellow in alkali.
  • Bromothymol blue: yellow in acid, blue in alkali.

The Strength of Acids and Alkalis

• Strong acids and alkalis are fully ionized in water and are strong electrolytes.
• Weak acids and alkalis are partially ionized in water and are weak electrolytes.

The pH scale

• The strength of an acid or alkali is measured on the pH scale using a universal indicator.
• pH scale ranges from 0 to 14.
• pH values less than 7 indicate acidity, with lower values indicating stronger acidity.
• pH value of 7 is neutral.
• pH values greater than 7 indicate alkalinity, with higher values indicating stronger alkalinity.

Amphoteric Oxides and Hydroxides

• Amphoteric substance reacts with both acids and strong alkalis.
• Amphoteric oxide/hydroxide reacts with alkali to form salt and water.
• Amphoteric oxide/hydroxide reacts with acid to form salt and water.
• Aluminum hydroxide reacts with sodium hydroxide.
• Aluminum hydroxide reacts with hydrochloric acid.

Test your knowledge of acids and bases, focusing on identifying solution types based on indicator results, weak acid behavior, ion concentration, and metal reactions with hydrochloric acid. Explore strong acid reactions, ionic equations, suitable indicators for titrations, and the behavior of ethanoic acid.