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Chapter 8.1 & 8.2: Acids and Bases. What are acids: any compound that increases the number of hydronium ions (H 3 O + ) when dissolved in water. Hydronium forms when hydrogen ions from the compound combine with water molecules You can also think of an acid as making H + .
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Chapter 8.1 & 8.2: Acids and Bases • What are acids: • any compound that increases the number of hydronium ions (H3O+) when dissolved in water. • Hydronium forms when hydrogen ions from the compound combine with water molecules • You can also think of an acid as making H+. • H3O+ H2O + H+
Acids HNO3 + H2O H3O+ + NO3-
Acids • This process of breaking down in water is called ionization. • Acids that completely ionize called strong acids (e.g hydrochloric, HCl). • Ones that do not are called weakacids(e.g. citric acid) • Movie: Strength of Acids and Bases
What is a base? • Any compound that increases the number of hydroxide (OH-) ions when dissolved in water. • They do this through dissociation. NH3 + H2O NH4+ + OH-
Bases • There are strong and weak bases, too, based on whether they completely dissociate or not. • Strong acids and bases are also strong electrolytes. That means that they conduct electricity, due to the ions they make. • Note: Whether an acid or base is strong or weak has nothing to do with its “damage” ability! Concentration is important, too. A strong acid/base can be diluted and not very dangerous.
acid or a base? • acid • HCl H2SO4 • Ca(OH)2 H3PO4 • NaOHLiOH • HCO3 NH4OH • acid • base • acid • base • base • acid • base • If it starts with H…it’s usually an acid • If it ends in OH…it’s usually a base
What is pH? • It stands for PouvoirHydrogene, the power of hydrogen. • It’s a measure of the concentration of Hydrogen ions in a solution • Usually goes from 0 – 14, 7 = neutral • Acids < 7 < Bases • The farther away from 7 you get, the more powerful/dangerous the acid or base.
What is pH? • pH scale is logarithmic…goes by factor of 10, e.g. 4 is 10 times more acidic than 5 and 100 times more acidic than 6 • You can use an indicator (chemical that changes color) to tell whether something is an acid or base. • Acids and bases are equally dangerous, depending on their pH. Something with a pH of 1 will hurt you just as much as 14! • Movie: pH
Acid-base Reactions • When an acid and base are mixed together, it is called a neutralization reaction. • It forms water (from H+ and OH-) and a salt (from the other ions). • Movie: Neutralization reaction
What salt would form from • NaCl • HCl + NaOH • H2SO4 + Ca(OH)2 • HBr + Ca(OH)2 • H3PO4 + Al(OH)3 • HF + Al(OH)3 • H2SO4 + NaOH • HNO3 + NH4OH • CaSO4 • CaBr2 • AlPO4 • AlF3 • Na2SO4 • NH4NO3 • Once the H and OH are gone, whatever is left makes the salt. But the charges still have to balance.
Acid-base Reactions • You can add one to the other in the presence of an indicator to tell when it is neutralized. This is called a titration. • The pH where it is neutralized is called the equivalence point. • The equivalence point is not always pH 7, e.g. weak acid + strong base…pH > 7 (basic)
If you graph a titration… • At what concentration of KOH is the equivalence point? • How can you tell? • This would also tell you the original concentration of acid. • Note how quickly the pH changes from about 4 to 10!
