CHEMISTRY 161
Chapter 4
www.chem.hawaii.edu/Bil301/welcome.html
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+35.45 g/mol] = 0.34 mol
2. convert volume into liters
350 ml = 0.350 l
3. calculate molarity
0.97 M
NaCl(s) → Na+(aq) + Cl-(aq)
0.97 M0.97 M +
1.94 M
(with respect to ions)
reference system in case of strong electrolytes
0.97 M
Ba(NO3)2(s) → Ba2+(aq) + 2 NO3 -(aq)
1.5 M 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 Mdilution
‘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 ------------ 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
moles of solute before dilution = moles of solute after dilution
i: initial conditions
f: final condiotions
Mi Vi = Mf Vf
1.precipitation reactionsgravimetric analysis
2. acid-base reactions titrations
3. redox reactionstitrations
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
Ba2+ or SO42- BaSO4
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
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
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
unknownstandard solution
(purple)
light pink
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