Describing Acids and Bases Chapter 6 – Section 3 & 4: Describing Acids and Bases

Acids Acids are solutions that give off H+ ions in water. Ex.: HCl H2O H+ + Cl-

Examples of acids:. HCl (Hydrochloric Acid) – Stomach Examples of acids: * HCl (Hydrochloric Acid) – Stomach * H2SO4 (Sulfuric Acid) – Batteries * H3PO4 (Phosphoric Acid) – Pop * HNO3 (Nitric Acid) – Fertilizers

Bases Bases are solutions that give off OH- ions (hydroxide ion) in water. Ex. NaOH Na+ + OH-

Examples of Bases:. NaOH (Sodium Hydroxide) – cleaning products Examples of Bases: * NaOH (Sodium Hydroxide) – cleaning products * KOH (Potassium Hydroxide) – Soap Making (K+ + OH-) * Ca(OH)2 (Calcium Hydroxide) – Cement (Ca2+ + OH- + OH-) * Mg(OH)2 (Magnesium Hydroxide) – Antacids * NH4OH (Ammonium Hydroxide) - Ammonia

Properties of Acids and Bases 1. Tastes sour 1. Tastes bitter 2. Feels squeaky 2. Feels slippery 3. Turns litmus paper red 3. Turns litmus paper blue 4. Reacts with metal and produces H2 gas 4. Does not react with metals 5. Reacts with carbonates and produces CO2 gas 5. Does not react with carbonates 6. Release H+ ions in water 6. Release OH- ions in water 7. pH of 0 to 6.9 7. pH of 7.1 to 14

Indicators of Acids and Bases Indicators are organic compounds whose color is dependent on the H+ ion concentration of the solution. Indicators change color as a chemical gains or loses H+ ions.

Types of Indicators: Litmus paper is an indicator that turns red/pink in an acid and blue in a base. Phenolphthalein is an indicator that is colorless in an acid, but turns pink in a base. Purple cabbage is a natural indicator that turns pink in an acid and green or blue in a base. It stays purple if the solution is neutral.

Types of Indicators continued… pH paper is a mixture of indicators. It is used to test the strength of an acid or base. The pH ranges from 0 – 14. pH meter is used to accurately determine the concentration of H+ ions in a solution in quantitative vales (numbers).

What is pH? pH = Measuring the H+ ion concentration The more H+ in a solution the more acidic. The more OH- in a solution the more basic.

pH Scale The pH scale is a tool chemists use to determine the concentration of H+ ions in a solution. The pH scale range is 0 – 14.

Acids range from 0 to 6.9 0 = strong acid 6.9 = weak acid Bases range from 7.1 to 14 7.1 = weak base 14 = strong base Neutrals have a pH of 7.0

HCl in the presence of water H+ + Cl- The # of H+ in water tells how acidic the solution is. NaOH in the presence of water Na+ + OH- The # of OH- in water tells how basic the solution is. This is ionization = breaking apart to produce ions in water.

Strengths of Acids and Bases: The strength of an acid or a base refers to how easily they produce ions in water (break apart).

HCl is a strong acid & a strong electrolyte because all the H+ break away from Cl- when added to water. Acetic acid (HC2H3O2) is a weak acid & a weak electrolyte because not many H+ break away when added to water.

NaOH is a strong base because all the OH- break away from the Na+ in water. Mg(OH)2 is a weak base because not many OH- break away when added to water.

Neutralization Reaction = Acid + Base reactions A neutralization reaction (acid + base) produces salt + water. HNO3 + KOH KNO3 + H2O Acid + Base Salt + water 0 14 7 7

If the right amounts of base and acid were added to each other all the products will be salt and water and the pH will be 7.0, i.e. complete neutralization.

Neutralization occurs when you take an antacid for heartburn (too much HCl), acid reflex disease (HCl in esophagus), ulcers (bleeding stomach sores from too much HCl production). 2HCl + Mg(OH)2 MgCl2 + 2H2O

Acid Rain: Normal rainfall is slightly acidic (pH 5.5) due to presence of CO2 in the air form carbonic acid. Pollutants (NO2 + SO2) in the air react with the water and form nitric acid and sulfuric acid.

These acids drop the acidity of the rain to 5. 5 – 3 These acids drop the acidity of the rain to 5.5 – 3.0 and produce acid rain. Acid rain can damage buildings and kill trees and fish in lakes.