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Atkins and Jones

Lets walk through them all together:. Atkins and Jones. Strong/Strong Titration Calculations. If 100. mL of a Mg(OH) 2 solution is titrated with 25.0mL of 2.00 M HCl ….. What is the pH at the equivalence point? How many moles of Mg(OH) 2 were initially present?

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Atkins and Jones

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  1. Lets walk through them all together: Atkins and Jones

  2. Strong/Strong Titration Calculations • If 100. mL of a Mg(OH)2 solution is titrated with 25.0mL of 2.00 M HCl….. • What is the pH at the equivalence point? • How many moles of Mg(OH)2 were initially present? • What was the concentration of Mg(OH)2?

  3. Strong/Strong Titration Calculations • A student weighs 1.823 g of an unknown strong acid into a beaker with 10mL of water. It is titrated to equivalence with 50.0mL of 1.0M NaOH. What was the molecular mass of the acid.

  4. Conjugate Acid/Base pairs • Acids lose a proton to become the conjugate base. • Bases gain a proton to become it’s conjugate acid • All acid/base reactions have both an acid and a base in them? So what is the base and conjugate acid in the first reaction? What is the acid and conjugate base in the second reaction? Conjugate Base Acid Conjugate Base Conjugate Acid Base Acid

  5. Important Relations • Relations between [H+], [OH-], Kw, pH and pOH pH=7 @25oC H2O ]=1x10-7 @25oC K]=1x10-14 @25oC Taking the log of both sides: Can you just memorize this without understanding it? What happens if the temperature changes?

  6. Kw Example Problem If water is heated and placed under pressure it has a pH of 6.8. Find the Kw of water under these conditions. Is it acidic, basic or neutral? ] K] kw=[10-6.8] [10-6.8]=2.5x10-14

  7. Weak and Strong Acid and Bases: Compare and Contrast Weak acids and bases ionize to a very limited extent. For strong acids and bases, we assume they completely ionize. Equilibrium lies far to the right How do I know which is strong and weak? Very small Ka Very Large Ka Memorize the strong, the rest are weak Equilibrium lies far to the left

  8. What happens to Ka as the strength of the acid increases? vs The larger the Ka the stronger the acid. https://todaysmeet.com/1CBrindley

  9. What happens to Kb as the strength of the base increases? If a base is stronger, which way does the equilibrium shift? It shifts to the right, so what happens to the amount of each product? So for a stronger base, Kb is higher!!! https://todaysmeet.com/1CBrindley

  10. Ranking: • Rank the following solutions in order of increasing acidity. Assume the concentration for each is the same, and that all are within solubility limits. NH2(CH3)2+ NH(CH3)2 NaOH HCl CH3COOH Ca(OH)2 Strong acid Weak acid Strong Base Weak Base

  11. Ranking: • Rank the following solutions in order of increasing acidity. Assume the concentration for each is the same, and that all are within solubility limits. Weak acid Strong Base Weak Base Strong acid NH2(CH3)2+ NaOH NH(CH3)2 HCl Ca(OH)2 CH3COOH Ka=1.8x10-5

  12. Acid/Base Conceptual Understanding Questions: In what range must the pH of a 0.17M solution of a weak acid fall? pH<7 pH>-log(0.17) pH= 0.77-7 What must be true about the [H+] of a weak acid solution @25oC? Neutral gives [H+]=[OH-]=10-7 Acidic has more [H+] so: >10-7 What must be true about the [OH-] of a weak acid solution? Neutral gives [H+]=[OH-]=10-7 Acidic has less [OH-] so: <10-7

  13. Percent Ionization: Pictorial Representation Dissociated Acid: 3 Original Acid: 14 % ionization= 3/14*100%= 21.4%

  14. Example: The percent dissociation of a 0.800 M aqueous monoprotic weak acid is 0.10%. What is the Ka value for the acid? HA 0M 0M 0.8 M I C E 8x10-4M 8x10-4M 0.8-8x10-4M = 8.00x

  15. Polyprotic acids: Poly=many protic=protons polyprotic=many proton atoms Ka1 K=Kw/Ka1 K=Kw/Ka2 Ka2 What is the Kb of CO32-?

  16. Molecular Structure and Strength of Acids Hydrohalic Acids • HX, where X designates a halide (F, Cl, Br, I) • Two competing forces: Enthalpy and Polarity • Enthalpy of HI is much lower than HF, says HI is strongest • Bond polarity would make it seem as if HF should be the strongest • So which wins? • Bond enthalpy strong weak

  17. Generalization of Acid Strengths Other Acids REMEMBER The more you stabilize the anion, the stronger the acid • Different Central Atoms, Same oxidation number (aka same number of attached groups) • Strength increases with increasing electronegativity of central atom. • Example: HClO3>HBrO3 • Same central atom, different number of attached groups • Increases as oxidation number of central atom increases • Example: HClO4 >HClO3>HClO2>HClO < +5 +7 +3 +1 Oxidation number Strength of acid

  18. Buffers • Acid and its conjugate base, or a base and its conjugate acid • Or some combination of components which create this. (next slide) • It works by converting a strong acid into a weak acid, or a strong base into a weak base. • A strong base can’t exist in solution with a weak acid it must react • A strong acid can’t exist in solution with a weak base it must react

  19. Can you make a buffer with? • NH3 and HCl? Yes! How: when NH3 and HCl react, they form NH4+ NH3+ H+ → NH4+ Gives us a conjugate acid base pair 0M 0.20M 0.10M I C F +0.10M -0.10M -0.10M 0.10M 0.10M 0M

  20. Buffer Calculation Example A 100 mL buffer solution is 0.100M Nitrous acid and 0.100M Sodium nitrite. Calculate the pH if 0.005 moles of NaOH is added to the solution calculate the pH of 0.002 moles of HCl is added to the solution. calculate the pH of 0.0150 mols of NaOH is added to the solution. Assume no change in volume.

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