CHEMISTRY 161 Chapter 4

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

qualitatively quantitatively molarity

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

M = moles of solute liters of solution [ ] mol l What is the Molarity of a solution of 20 g NaCl in 350 ml of water? 1.convert grams into moles 20g / [22.99 g/mol g/mol] = 0.34 mol 2. convert volume into liters 350 ml = l 3. calculate molarity 0.97 M

NaCl(s) → Na + (aq) + Cl - (aq) 0.97 M M (with respect to ions) reference system in case of strong electrolytes 0.97 M Ba(NO 3 ) 2 (s) → Ba 2+ (aq) + 2 NO 3 - (aq) 1.5 M 3.0 M

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

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 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 moles NaCl x l of a 4.0 M solution moles NaCl x = 390 ml

moles of solute before dilution = moles of solute after dilution i: initial conditions f: final condiotions M i V i = M f V f

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

1. Gravimetric Analysis a precipitation method based on the determination of weight of a substance of known composition Ag + or Cl - AgCl Ba 2+ or SO 4 2- BaSO 4

Gravimetric Analysis weigh sample (NaCl) dissolve sample in water add precipitating reagent in excess (AgNO 3 ) filtration-separate AgCl from liquid wash precipitate dry and weigh to constant weight quantitatative analysis

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) + H 2 O(l) unknown 1 M standard

Conductivity Analysis HCl(aq) + NaOH(aq) → NaCl(aq) + H 2 O(l) Λ (H + ) >> Λ (Na + ) Λ (OH - ) >> Λ (Cl - )

3. Redox Titration determine the concentration of a sample ion by adding stepwise a solution of a known reagent 5 Fe 2+ + MnO H + → Mn Fe H 2 O unknown standard solution (purple) light pink

1.precipitation reactions 2. acid-base reactions 3. redox reactions SUMMARY

Homework Chapter 4, p problems