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Acids and Bases

Acids and Bases. A primer. Why are Acids and Bases Important?. They occur in every solution with water Especially since they often come from water They have exciting reactions with metals and other compounds They can eat up metals and can cook fish

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Acids and Bases

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  1. Acids and Bases A primer

  2. Why are Acids and Bases Important? • They occur in every solution with water • Especially since they often come from water • They have exciting reactions with metals and other compounds • They can eat up metals and can cook fish • They have subtle, but very important effects on your body • Your breathing rate is determined by the acidity of your blood, for example

  3. A First Definition:(Arrhenius) • Acids donate H+ ions to water: • HCl H+(aq) + Cl- (aq) • HNO3  H+(aq) + NO3- (aq) • Bases donate OH- ions to water • NaOH Na+(aq) + OH- (aq) • NH4OH   NH4+(aq) + OH- (aq)

  4. Important Acids and Basesknow them forever Acids • HCl- Hydrochloric Acid • HNO3 – Nitric Acid • H2SO4- Sulfuric Acid • H3PO4- Phosphoric Acid • CH3COOH- Acetic acid • HF- Hydrofluoric Acid Bases • NaOH- Sodium Hydroxide • NH3 – Ammonia • NH4OH – Ammonium Hydroxide

  5. Properties of Acids Acids • React with water to make hydronium and an anion • HCl + H2O  H3O+ and Cl- • Since all acid reactions occur in water, this often left out • Please view H3O+ as more or less the same as H+ • React w/ metals to make salt and hydrogen: • 2HCl + Zn  ZnCl2 + H2 • React with bases to make salt and water • HCl + NaOH  NaCl + H2O • Taste sour (the sourness of food is literally acidity)

  6. Properties of Bases Bases • Dissociate in water to make hydroxide and a cation • NaOH Na+ and OH- • Most acid/base reaction occur in water, so one is always considering the ions. • React w/ proteins and lipids (fats) to break them apart): • They are used to “straighten” hair and can react with fat to make soap. Can also be used to dissolve hair in drains.) • React with acids to make salt and water • HCl + NaOH  NaCl + H2O • Taste bitter (your “bitter” taste buds detect OH-)

  7. Reactions of Water • Water itself can and does produce acids and bases • The process is called “auto-ionization”. • H2O + H2O  H3O+ + OH- • Notice that is an equilibrium process. The products are rare in water, only about 2 parts per billion water molecules. Water is much more stable. • The Keq for water is [H3O+] [OH-] = 1.00 x 10-14 • (Why is H2O left out? Because it is a liquid!) • The Keq of water is often referred to as Kw (“w” for water)

  8. Concentrations • Every drop of water has some H+ ions and some OH- ions. How much depends on what, if anything, else is in the drop. • In pure water, the H+ and OH - come from the water itself….the amounts will be equal. • So if [H3O+] = X , then [OH-] will also be equal to X • And… if the Keq for water is [H3O+] [OH-] = 1.00 x 10-14 • Then X * X = 1.00 x 10-14 • So in pure water, [H3O+] = 1.00 x 10-7 (the square root) • This is where pH of pure water = 7 comes from (more later)

  9. Concentrations, continued • The amount of acids and bases is measured by pH scale. (We will discuss the scale more in the next class) • Because of the Kw, H+ will be inverse of OH- • If you add an acid to water… • The [H+] will be high, the [OH-] will be low, the pH will be below 7; the solution will be “acidic” • If you add a base to water… • The [OH-] will be high, the [H+] will be low, the pH will be above 7; the solution will be “basic” or “alkaline”

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