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Acids and Bases

Acids and Bases. Video 11.1. Acids and Bases. What is an electrolyte?. A substance that dissolves in water and conduct electricity. Acids and bases are electrolytes. Arrhenius. Acid : Substance that, when dissolved in water, increases the concentration of hydrogen H +

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Acids and Bases

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  1. Acids and Bases

  2. Video 11.1 Acids and Bases

  3. What is an electrolyte? A substance that dissolves in water and conduct electricity. Acids and bases are electrolytes.

  4. Arrhenius • Acid: Substance that, when dissolved in water, increases the concentration of hydrogen H+ (or hydronium H3O+) ions. • Acids have a sour taste and can burn your skin. • Acids react vigorously with metals to make H2 • pH is less than 7 • On table K

  5. Arrhenius • Base:Substance that, when dissolved in water, increases the concentration of hydroxide ions. • Bases have a bitter taste and are corrosive. • pH>7 • On Table L

  6. Arrhenius • If an acid is added to a base, it results in neutralization, where all properties of the acid and base are lost. The products are a salt and water. NaOH + HCl H2O + NaCl Salt is another name for solid ionic compounds containing elements other than H+ and OH-. Salts are electrolytes with high mp and bp.

  7. Label and name the acid, base and salt: • H2SO4 + LiOH H2O + Li2SO4 • KOH + HNO3  KNO3 + H2O Salt Acid Base Salt Acid Base

  8. Identify the salt produced: • NaOH + HF  • Ca(OH)2 + H2SO4  NaF H2O + H2O + CaSO4 Make sure you check your compounds with the criss cross rule for ions!

  9. Video 11.2 Alternate Acid Base Theory

  10. Brønsted–Lowry : BAAD • Acid: Proton donor • Base: Proton acceptor Protons refer to hydrogen ions. H+ H

  11. If it can act as either an acid or a base it is amphiprotic. HCO3− HSO4− H2O These all have hydrogen atoms to donate and a negative charge that would attract H+

  12. What Happens When an Acid Dissolves in Water? • Water acts as a Brønsted–Lowry base and removes a proton (H+) from the acid. • As a result, the conjugate base of the acid and a hydronium ion are formed.

  13. Conjugate Acids and Bases: • Reactions between acids and bases always yield their conjugate bases and acids.

  14. Acid and Base Strength • Strong acids and bases are completely dissociated in water to make a lot of H+or OH-. • Weak acids and bases only dissociate partially in water to make a small amount of H+or OH-. • How is strength different from concentration?

  15. Strength versus Concentration • Strength refers to the amount of ions a substance makes when it breaks down. • Concentration refers to the amount of the substance initially, before it breaks down. This is usually measured in molarity (mol/L).

  16. Video 11.3 pH and indicators

  17. pH

  18. How Do We Measure pH? • For less accurate measurements, one can use • Litmus paper • “Red” paper turns blue above ~pH = 8 • “Blue” paper turns red below ~pH = 5 • An indicator

  19. How Do We Measure pH? For more accurate measurements, one uses a pH meter, which measures the voltage in the solution.

  20. Earth’s Natural Litmus • Hydrangeas are blue when the acidity of the soil is between 5-5.5 and red if the acidity is between 6.5-7.5. A mix of colors can be seen between 5.5-6.5.

  21. pH is a logarithmic scale • If the pH goes up one, the concentration of hydrogen ions decreases by 10. The solution is more basic. • If the pH goes down one, the concentration of hydrogen ions increases by 10. The solution is more acidic.

  22. Examples • If the pH changes from 3 to 4, how much more basic is the solution? • If the pH = 3 and the hydrogen concentration increases by 100 times, what is the new pH? • If the pH = 8 and the hydrogen ion concentration decreases by 10,000 times, what is the new pH?

  23. Indicators • If NaOH is tested with methyl orange, what color will it be? • At what pH will bromocrescol green turn yellow? • What type of solution will turn bromothymol blue, yellow? • At what pH will both bromothymol and thymol blue be yellow? yellow 3.8 acidic 7.6-8

  24. Examples • Why won’t methyl orange be good at determining the difference between an acid and a base? • Which indicator is the best to test the difference between a strong and weak base? • What color change will be seen if NaOH is added to HCl with methyl orange? • What color change will be seen if nitric acid is added to lithium hydroxide using bromocrescol green? Bases and acids can both be yellow Thymol blue Red to yellow Blue to yellow

  25. Video 11.4 Titrations

  26. Neutralization • ACID + BASE  SALT + WATER • Salt is another name for any ionic substance. They can conduct electricity. • HCl + NaOH  NaCl + H2O acid base salt

  27. Titrations • Titrations are used to find the concentration of a solution. Usually the concentration of the base is unknown, so a known acid is added to the base until the solution neutralizes. • The endpoint, or the point where the solution is neutral and the titration is over, is marked by a faint pink color in the solution (due to phenolphthalein).

  28. Titrations • To calculate the molarity of the unknown use the formula on Table T: MAVA=MBVB

  29. Examples • What is the molarity of NaOH if 100.mL of 3.00M HCl is titrated with 200.mL of NaOH? MAVA=MBVB (3.00)(100) = x(200) x = 1.50M • What is the molarity of 100.0mL HCl if it is neutralized by 250mL of 2.0M NaOH? MAVA=MBVB (x)(100) = (2.0)(250) x = 5.0M

  30. Exceptions • The titration formula only works if the acid and the base have equal numbers of H+ and OH-. If not, the acid side must be multiplied by the number of hydrogen ions and the base side must be multiplied by the number of hydroxide ions in the formulas. • What is the molarity of a solution of Ca(OH)2 if 750mL of it is titrated with 250mL of 3.5M H3PO4? 3MAVA = 2MBVB 3(3.5)(250) = 2(x)(750) x = 1.75M

  31. How much acid is in each burette? 15.4mL 0.6mL How much acid was released? 15.4-.6 = 14.8mL released from the burette.

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