Chemistry Notes: Acids and Bases

Properties of Acids and Bases taste sour (vinegar, lemons) aqueous solutions of acids are electrolytes cause indicators to change colors many metals react with acids to produce H2 gas react with bases to form a salt and water most formulas begin with H bitter taste (soap, unsweetened chocolate) bases are electrolytes in aqueous solution cause indicators to change colors feel slippery react with acids to form a salt and water often contain OH- , or ammonia NH3

Examples The bolded formulas below to STRONG acids and bases Common acids HCl HNO3 H2SO4 H3PO4 HC2H3O2 H2CO3 Common bases NaOH KOH Ca(OH)2 LiOH NH3

Measuring pH The pH of a substance can tell us if it’s an acid, a base, or neutral. pH is a measurement of the concentration of hydrogen ions (H+) in a solution. The more hydrogen ions present, the more acidic a substance is. Acids have large amounts of hydrogen ions, and low pH (pH < 7). Bases have small amounts of hydrogen ions, and high pH (pH > 7).

Another measurement, pOH, tells use the concentration of hydroxide (OH-) ions in a solution. The more hydroxide ions present, the more basic a substance is. Acids have small amounts of hydroxide ions, and high pOH (pOH > 7). Bases have large amounts of hydroxide ions, and low pOH (pOH < 7). Neutral substances have equal amounts of hydrogen and hydrogen ions (pH = 7, pOH = 7). The pH and pOH of a substance always add up to 14.

Practice: Are these solutions acidic, basic, or neutral?  pH = 5.6 NH3   Large concentration of OH- ions   Small concentration of H+ ions pOH = 3.2 pH = pOH H2SO4 NaOH Large concentration of H+ ions HCl

Practice: Are these solutions acidic, basic, or neutral? If the pH of a solution is 6, what is its pOH? Is it an acid or base?   If the pH of a solution is 4, what is its pOH? Is it an acid or base? If the pOH of a solution is 3, what is its pH? Is it an acid or base?

Indicators Indicators are substances that change color in solutions of different pH Help determine approximate pH

Phenolphthalein Colorless in acid Pink in base

Universal indicator Mixture of indicators Changes into different colors at each pH (rainbow) Red/orange in acid, blue/purple in base, green around pH = 7

Litmus paper Blue litmus turns red in acid Red litmus turns blue in base