Solutions, Acids, and Bases Section 3 Acids, Bases, and pH PHYSICAL SCIENCE Solutions, Acids, and Bases Section 3 Acids, Bases, and pH

Acids, Bases, and pH Objectives Compare and contrast acids and bases. Relate the pH of a solution to the concentration and strength of dissolved acid or base. Identify the products of neutralization reactions.

Acids Acids are substances that donate hydrogen ions (H+) to form hydronium ions (H3O+) when dissolved in water. An indicator is a compound that can reversibly change color in a solution, depending on the concentration of H3O+ ions. Acids turn blue litmus paper red. All acids can damage eyes or other sensitive areas of the body.

Acids Safety goggles, apron, and gloves are a must if working with acids in the laboratory – only dilute acids if possible. Acids conduct electricity, some better than others, because they form hydronium ions, H3O+, when they are dissolved in water. Nitric acid (HNO3) is a strong acid (has as many hydronium ions as the acid can possibly form) because it fully ionizes when dissolved in water.

Acids Acetic acid (CH3COOH) is a weak acid and does not conduct electricity as well as nitric acid because not all the acetic acid in the solution reacts to form ions in the solution. A molecule of acetic acid is shown to the left.

Some Common Acids Acid Formula Strength Uses for Dissolved Acid Hydrochloric (Muriatic) Acid HCl Strong Cleaning and food processing Sulfuric Acid H2SO4 Used in fertilizers and car batteries Nitric Acid HNO3 Making fertilizers and explosives Acetic (Ethanoic) Acid CH3COOH Weak Making vinegar and medicine Formic Acid HCOOH Dyeing textiles Citric Acid C6H8O7 Flavor for soda and candies

Bases A base is a substance that either contains hydroxide ions (OH-) or reacts with water to form hydroxide ions. Foods that contain bases taste bitter (acids taste sour) and bases are also slippery. Bases turn red litmus paper blue. Basic solutions can conduct electricity.

Litmus Paper as an Indicator

Bases Bases can be very dangerous if not diluted. Safety goggles, gloves, and apron should also be worn when working with bases, which also should be as diluted as possible. Potassium hydroxide (KOH) is a strong base and conducts electricity very well when dissociated in water. Example: KOH  K+ + OH-

Bases When ammonia gas is dissolved in water, water acts like an acid and donates a hydrogen ion which is accepted by the ammonia. The result is a mixture of dissolved ammonia, water, ammonium ions, and hydroxide ions – which produce a weak basic solution. An ammonia molecule is seen to the right.

Some Common Bases Base Formula Strength Uses for Dissolved Base Potassium hydroxide-potash KOH Strong Making soap and some drain cleaners, bleaching Sodium hydroxide-lye NaOH Making soap, paper textiles, and some drain cleaners Calcium hydroxide-lime Ca(OH)2 Making plaster, cement, mortar Ammonia NH3 Weak Making fertilizers and many cleaners Methylamine CH3NH2 Making dyes and medicines Pyridine C5H5N Making vitamins and medicines

pH pH is the measure of the hydronium ion concentration in a solution. Litmus paper can tell you if a solution is acidic or basic. The concentration of the hydronium ions is measured to determine the exact acidity (or alkalinity) or a solution. The pH of a solution is often critical for living things.

pH The pH of solutions can run from 0 to 14, neutral is 7.0. In a neutral solution, the concentration of hydronium ions equals the concentration of hydroxide ions. Solutions with a pH of less than 7.0 are acidic; solutions with a pH of greater than 7.0 are basic (alkaline). Each unit of pH represents a factor of 10 in hydronium ion concentration.

pH of Common Household Products

Neutralization Reactions A neutralization reaction is a reaction in which hydronium ions from an acid and hydroxide ions from a base react to produce water molecules. Strong acids and bases react to form water and a salt. Example: H3O+ + Cl- + Na+ + OH-  Na+ + Cl- + 2H2O A salt is an ionic compound composed of cations bonded to anions, other than oxide or hydroxide ions.

Neutralization Reactions When an acid reacts with a base, the hydronium ions react with the hydroxide ions to form water, and the other ions – positive ions from the base and negative ions from the acid – form a salt. The pH of a solution resulting from mixing an acid and a base depends on the amount of acid and base mixed as well as the strength of the acid and base involved.

Neutralization Reactions Some household products should never by mixed. Ammonia and bleach react to produce chloramine (NH2Cl), a poisonous substance. Vinegar and bleach combine to form chlorine gas (Cl2), another poisonous substance.