Acids and Bases

Chapter 3 Sections 2 + 3Pages 62-71

Acids and their Properties

• An acid is any compound that increases the number the of hydronium ions, H₃O⁺, when dissolved in water.

• Hydronium ions form when a hydrogen ion, H⁺, separates from the acid and bonds with a water molecule, H₂O.

Acids have a Sour Flavor

• Sour taste result of citric acid

• Most acids are corrosive (can destroy body tissue, clothing, etc.)

• Most acids are poisonous

Acids Change Colors in Indicators

• A substance that changes color in the presence of an acid or base is an indicator.

• An indicator is a compound that can reversibly change color depending on conditions such as pH

• Litmus paper strip usually blue and changes to red when an acid is added

Acids React with Metals

• Acids react with some metals to produce Hydrogen gas.

• Acids need reactive metals to produce the gas.

Acids Conduct Electric Current

• When acids are dissolved in water, they break apart and form ions in solution.

• Ions make the solution able to conduct an electric current.

• Car battery-sulfuric acid

Uses of Acids

• Sulfuric Acid: paper, paint, detergents, fertilizer

• Nitric Acid: fertilizer, rubber, plastics

• Hydrochloric Acid: make metal from ore separation, clean pools, in our stomach

• Hydrofluoric acid: etch glass• Citric Acid and ascorbic acid

(Vitamin C): juice• Carbonic acid and phosphoric

acid: soda

Bases and their Properties

• A base is any compound that increases the number of hydroxide ions, OH⁻, when dissolved in water.

• Hydroxide ions give bases their properties: soaps, bleach/detergents, baking soda.

• Properties include a bitter taste and slippery feel.

Bases and their Properties

• Bases change color in indicators. Changes red litmus paper to blue.

• Bases conduct an electric current because bases increase the number of hydroxide ions, OH⁻, in a solution.

• A hydroxide ion is a hydrogen atom and an oxygen atom bonded together. The extra electron gives the hydroxide ion a negative charge.

Uses of Bases

• Sodium hydroxide: makes soap and paper

• Calcium hydroxide: cement and plaster

• Ammonia: cleaner and fertilizer

• Magnesium hydroxide and aluminum hydroxide: antacids

Strengthens of Acids and Bases

• Strength is not the same as concentration.• Concentration is the amount dissolved in

water.• Strength depends on the number of

molecules that break apart when dissolved in water.

Strong Versus Weak Acids and Bases

• In a strong acid or base, all of the molecules of the acid or base break apart when the acid or base is dissolved in water.

• In a weak acid or base, only a few of the acid or base molecules break part when the acid or base is dissolved in water.

Acids, Bases and Neutralization

• The reaction between acids and bases is a neutralization reaction. (example- antacid meets stomach acid)

• The hydrogen ions H⁺ (from the acid) react with the hydroxide ions OH⁻ forming H₂O, water which is neutral. If the water evaporates then ions form compounds called salts.

The pH Scale

• An indicator, such as litmus, can identify whether a solution contains an acid or base.

• A pH is a value that is used to express the acidity or basically (alkalinity) of a system.

Less than 7: acid7: neutralGreater than 7: base

Using Indictors to Determine pH

• Indicators turn different colors at different pH levels.

• The color of the pH strip can be compared with colors on the indicator scale to determine the pH of the solution being tested.

pH and the Environment

• Rain pH (5.5-6)• Soil pH, some plants

grow better in either acidic or basic soil.

Salts and its Uses

• A salt is an ionic compound that forms when a metal atom replaces the hydrogen of an acid.

• Sodium Chloride• Sodium Hydroxide (lye

and baking soda)• Sodium nitrate (food

preservative)

More info on Acids and Bases

• http://www.chem4kids.com/files/react_acidbase.html