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CHEMISTRY 161 Chapter 4 chem.hawaii/Bil301/welcome.html

Explore the principles of molarity, dilution, and titrations in chemistry, including precipitation, acid-base, and redox reactions. Learn how to calculate molarity, conduct gravimetric analysis, and perform acid-base titrations. Find solutions to homework problems and understand the applications of these concepts.

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CHEMISTRY 161 Chapter 4 chem.hawaii/Bil301/welcome.html

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  1. CHEMISTRY 161 Chapter 4 www.chem.hawaii.edu/Bil301/welcome.html

  2. REVISION • precipitation reactions • 2. acid-base reactions • 3. redox reactions

  3. qualitatively molarity quantitatively

  4. 4.5. MOLARITY concentration of a solution [ ] moles of solute mol M = l liters of solution

  5. [ ] moles of solute M = mol liters of solution l What is the Molarity of a solution of 20 g NaCl in 350 ml of water? • convert grams into moles • 20g / [22.99 g/mol+35.45 g/mol] = 0.34 mol 2. convert volume into liters 350 ml = 0.350 l 3. calculate molarity 0.97 M

  6. NaCl(s) → Na+(aq) + Cl-(aq) 0.97 M 0.97 M 0.97 M + 1.94 M (with respect to ions) reference system in case of strong electrolytes Ba(NO3)2(s) → Ba2+(aq) + 2 NO3-(aq) 1.5 M 1.5 M 3.0 M

  7. [ ] moles of solute M = mol liters of solution l dilution ‘add water’ 4 M 2 M How many ml of a 4 M NaCl solution are necessary to prepare 2 l of a 4 M solution? ‘conservation of moles’

  8. How many ml of a 4 M NaCl solution are necessary to prepare 2.6 l of a 0.6 M solution? 1.0 l of a 0.6M solution ------------ 0.6 moles NaCl 2.6 l of a 0.6 M solution ------------ x moles NaCl x = 1.56 moles NaCl 1.0 l of a 4.0 M solution ------------ 4.0 moles NaCl x l of a 4.0 M solution ------------ 1.56 moles NaCl x = 390 ml

  9. Mi Vi = Mf Vf moles of solute before dilution = moles of solute after dilution i: initial conditions f: final condiotions

  10. APPLICATIONS • precipitation reactions • gravimetric analysis • 2. acid-base reactions • titrations • 3. redox reactions • titrations (lab course)

  11. 1. Gravimetric Analysis a precipitation method based on the determination of weight of a substance of known composition Ag+ or Cl- AgCl Ba2+ or SO42- BaSO4

  12. Gravimetric Analysis • weigh sample (NaCl) • dissolve sample in water • add precipitating reagent in excess (AgNO3) • filtration-separate AgCl from liquid • wash precipitate • dry and weigh to constant weight quantitatative analysis

  13. 2. Acid-Base Titration determine the concentration of an acid (base) by adding stepwise a solution of a known concentration of a base (acid) HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l) unknown 1 M standard

  14. Conductivity Analysis HCl(aq) + NaOH(aq)→ NaCl(aq) + H2O(l) Λ (H+) >> Λ (Na+) Λ (OH-) >> Λ (Cl-)

  15. 3. Redox Titration determine the concentration of a sample ion by adding stepwise a solution of a known reagent 5 Fe 2+ + MnO4- + 8 H+→ Mn2+ + 5 Fe3+ + 4 H2O standard solution (purple) light pink unknown

  16. SUMMARY • precipitation reactions • 2. acid-base reactions • 3. redox reactions

  17. Homework Chapter 4, p. 128-140 problems

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