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Acid Base Class #4

Acid Base Class #4. OB: some of the loose ends of acids + bases, describing how acid base indicators work, and review of the titration math, including slightly more complex problems with different H +1 : OH -1 ion ratios. .

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Acid Base Class #4

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  1. Acid Base Class #4 OB: some of the loose ends of acids + bases, describing how acid base indicators work, and review of the titration math, including slightly more complex problems with different H+1 : OH-1 ion ratios.

  2. Acid Base indicators are mostly weak acids (some could be weak bases). When you put these indicators into solutions containing H+1 ions or OH-1 ions, they will undergo a LeChatelier's Principle shift forward or reverse. Since the indicator molecules and the ions they form are different colors, they will be one color or the other, depending upon the acid or base strength. Let’s look at the molecule phenolphthalein, since we used it in lab. It’s a weak acid, which means it’s a molecule with a H+1 ion that could ionize off the molecule. The formula for phenolphthalein is: HC20H13O4

  3. Phenolphthalein is a weak acid, with formula HC20H13O4 H+1(AQ) + C20H13O4-1(AQ) water colorless molecule pink anion If we ADD BASE, which way does this shift? In excess base, the hydrogen ions are united with hydroxides from the base forming water, making the reverse reaction less likely – so it shifts forward, producing more pink anions. This is why phenolphthalein turns pink with bases.

  4. Phenolphthalein is a weak acid, with formula HC20H13O4 H+1(AQ) + C20H13O4-1(AQ) water colorless molecule pink anion If we ADD ACID, which way does this shift? In excess acid, the anions which are pink have an easier time finding the hydrogen ions, shifting this equilibrium to the molecular form, which is colorless. More collisions = faster reaction

  5. Svante Arrhenius won a Nobel Prize for his theory of acids and bases. Bronsted + Lowry made a name for themselves with ammonia being a base and their “alternate theory”. Yet another way to “understand” acids, although thankfully with no names attached, is this: The hydrogen ions from the acid join water molecules this way: H+1 + H2O H3O+1 The acid exists “as” part of a water molecule, called the hydronium ion. The H+1 ion becomes one with water. You can believe this if you like, you might see it on the regents, but it seems unnecessary. Extra vocabulary… Hydronium ion: a theoretical model for acids, whereby the hydrogen ions become one with water and exist as H3O+1

  6. Acids can be described as: H+1(AQ) Svante Arrhenius was right Any compound that donates a H+1 ion, according to the Bronsted-Lowry theory(NH3, ammonia is a base because it ACCEPTS a H+1 ion) H3O+1 the weird hydronium ion p+1 or just as protons (what really is a hydrogen ion, if a hydrogen ion is a proton plus one electron, and the electron ionizes away to an anion, all that’s left is a proton.)

  7. Write 4 balanced chemical equations for these word equations… Hydrochloric acid + potassium hydroxide yields… Sulfuric acid + beryllium hydroxide yields… Nitrous acid + magnesium hydroxide yields… Acetic acid + sodium hydroxide yields…

  8. Write 4 balanced chemical equations for these word equations… HCl(AQ) + KOH(AQ) KCl(AQ) + HOH(L) H2SO4(AQ) + Be(OH)2(AQ) CaSO4(AQ) + 2HOH(L) 2HNO2(AQ) + Mg(OH)2(AQ) Mg(NO2)2(AQ) + 2HOH(L) HC2H3O2(AQ) + NaOH(AQ) NaC2H3O2(AQ) + HOH(L)

  9. Show the dissociation for sulfurous acid into water, then the dissociation of potassium hydroxide in water as well. Use phase symbols.

  10. Show the dissociation for sulfurous acid into water, then the dissociation of potassium hydroxide in water as well. Use phase symbols. H2SO3(G) H+1(AQ) + H+1(AQ) + SO3-1(AQ) KOH(S) K+1(AQ) +OH-1 (AQ) water water

  11. How many milliliters of 1.25 M NaOH base can 12.0 mL of 2.50 M HCl acid neutralize?

  12. How many milliliters of 1.25 M NaOH base can 12.0 mL of 2.50 M HCl acid neutralize? (MA)(VA) = (MB)(VB) (2.50 M)(12.0 mL) = (1.25 M)(VB) 24.0 mL = VB This is an important time to point out that this acid is monoprotic (one H+1) per molecule. The base is also a “single hydroxide” base.

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  14. How many milliliters of 1.25 M NaOH base can 12.0 mL of 2.50 M H2SO4 acid neutralize? Note: this is a “double” acid AKA: diprotic, and a single hydroxide base. Let’s look at the back of our reference tables NOW. What does the MA and the MB REALLY mean??? MA is the molarity of the H+1 ions, not of the acid molecules H2SO4 has 2H+1 ions per molecule. 2.50 M H2SO4 solution has 2 x 2.50 moles H+1 ions in solution.

  15. This child will become a famous chemist, note the mustache. Actually, he’s for comic relief, don’t work too hard today. But don’t slow down yet either. Stop texting!

  16. How many milliliters of 1.25 M NaOH base can 12.0 mL of 2.50 M H2SO4 acid neutralize? To do this problem, we start with the same formula for titration math, but we make an important adjustment to take into account the “double acid” which has 2x the number of H+1 ions because it’s diprotic. The base is still a “single base” so we’ll multiply that side by a one. (MA)(VA) = (MB)(VB) For problems when the H+1 = OH-1 in the acid and base. Here… (2)(MA)(VA) = (MB)(VB)(1)

  17. How many milliliters of 1.25 M NaOH base can 12.0 mL of 2.50 M H2SO4 acid neutralize? (2)(MA)(VA) = (MB)(VB)(1) (2)(2.50 M)(12.0 mL) = (1.25 M)(VB)(1) 48.0 mL = VB Think: it will take twice as much base to neutralize this because the acid contains twice as many hydrogen ionsas HCl would.

  18. 2 more problems, and then, we’re done… How many mL of H3PO4 acid of 1.15 M is needed to exactly neutralize 56.0 mL of2.50 M Mg(OH)2 base?

  19. How many mL of H3PO4 acid of 1.15 M is needed to exactly neutralize 56.0 mL of2.50 M Mg(OH)2 base? (triple acid, double base) (3)(MA)(VA) = (MB)(VB)(2) (3)(1.15 M)(VA) = (2.50 M)(56.0 mL)(2) VA = 81.2 mL

  20. How many mL of 0.760 M NaOH is required to neutralize 145 mL of 4.33 M HCl acid?

  21. How many mL of 0.760 M NaOH is required to neutralize 145 mL of 4.33 M HCl acid? (MA)(VA) = (MB)(VB) (4.33 M)(145 mL) = (0.760 M)(VB) 826 mL = VB Both of these are single: a monoprotic acid (single) with a single hydroxide base, no math correction needed.

  22. Read the diary, do the 2 drills on the acid base page linked from the bottom of the home page, hand in the solutions lab and the clock lab, and get going on the acid base titration lab (due Friday). We celebrate Acids and Bases on Thursday

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