Jana Fauknerová Matějčková
[email protected]
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Expression of concentration
• molar concentration
• percent concentration
• conversion of units
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•
Osmotic pressure, osmolarity
Dilution of solutions
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Solute
• a substance dissolved in a solvent in forming a solution
•
Solvent
• a liquid that dissolves another substance or substances
to form a solution
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Solution
• a homogeneous mixture of a liquid (the solvent) with a
gas or solid (the solute)
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Concentration
• the quantity of dissolved substance per unit quantity of
solution or solvent
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Relative atomic /molecular mass (Ar/Mr)
• the ratio of the average mass per molecule of the naturally
occurring form of an element or compound to 1/12 of the
mass of 12C atom
– Mr = sum of relative atomic masses (Ar) of all atoms that
comprise a molecule
– MW (in g/mol) = Mr (no units)
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Dilution
• process of preparing less concentrated solutions from a
solution of greater concentration

density ()
m (grams)
 g/cm3 
V (cm3)
 the mass of a substance per unit of volume

amount of substance (n)
m( g )
n (mol ) 
M( g / mol )
 a measure of the number of entities present in a substance (in
moles)

Avogadro constant (NA)
 the number of entities in one mole of a substance (NA = 6.022x1023)

molar concentration (= molarity)
units = M = mol/L
1M solution
 1 mol of a solute is found in 1000 mL (= 1L) of the solution
0,5M solution
 0,5 mol of a solute is found in 1000 mL (= 1L) of the sol.

percent concentration
% = g/100g
1% solution
 1 g of a solute is found in 100 g of the solution
0,5% solution
 0,5 g of a solute is found in 100 g of the solution

Molar concentration or Molarity
 express the number of moles of a substance per liter of a
solution
n (mol )
c(mol / l ) 
V(l )
number of moles / 1000 mL of solution
DIRRECT PROPORTIONALITY
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1M NaOH MW = 40 g/mole
=> 1M solution of NaOH = 40g of NaOH / 1L of solution
0,1M solution of NaOH = 4g of NaOH / 1L of solution
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Preparation of 500 mL of 0,1M NaOH:
0,1M solution of NaOH = 4g of NaOH / 1 L of solution
2g of NaOH / 0.5 L of solution
! DIRRECT PROPORTIONALITY !

In 300 ml of solution is dissolved 17.4 g of
NaCl. What is the molarity of the solution? Mr
(NaCl) = 58
1M


2.5 L solution contains 4.5 g of glucose. What
is the molar concentration of solution? Mr
0,01M
(glucose) = 180
How many mg of glycine is contained in a
100mL 3 mM of its solution? Mr (glycine) = 75
22,5 mg

How many grams of solid NaOH is needed to
prepare 0.5 L of 0.5 M solution? Mr (NaOH) =
40
10g
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Problem 1: How many moles of Na+ ions are in 3.95 g of
Na3PO4? Mr (Na3PO4) = 163.94
– Na3PO4 → 3 Na+ + PO43–
3 moles 1 mole
– Moles of Na3PO4 = 3.95 / 163.94 = 2.4 x 10-2 moles
– Moles of Na+ = 2.4 x 10-2 x 3 = 7.2 x 10-2 moles
Solution of CaCl2, Concentration = 0,1M.
Calculate volume of the sol. containing 4 mmol of Cl-.
[20ml]
–
–
–
–
–
CaCl2 → Ca2+ + 2 Cl0.1 M = 0.1 mol
in 1 L
0.004 mol in X L
X = 0.004/0.1 = 0.04 L
But in one mole of the solution, there are two moles of Cl- → 0.04/2
= 0.02 L = 20 mL
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Molality
units mol.kg –1
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Osmolarity
units osmoles / L
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Osmolality
units mol.kg –1 or osmol.kg -1
– concentration in moles of substance per 1 kg of solvent
– concentration of osmotic effective particles (i.e. particles
which share in osmotic pressure of solution)
– it is the same (for nonelectrolytes) or higher (for electrolytes:
they dissociate to ions) as molality of the same solution
– the osmolarity of blood is 290 – 300 mosmol/l
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osmolality expressed in moles or osmoles per kg
• Isotonic solutions
– solutions with the same value of the osmotic pressure
(blood plasma x saline)
• hypertonic solutions
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higher concentration of ions in solution than in cells
• hypotonic solutions
• lower concentration of ions in solution than in cells
• Oncotic pressure
– osmotic pressure of coloidal solutions
– e.g. proteins
The figure is found at
http://en.wikipedia.org/wiki/Osmoti
c_pressure
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•
Example 1:
A 1 M NaCl solution contains 2 osmol of solute per liter of
solution.
NaCl → Na+ + Cl1 M does dissociate
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•
•
•
1 osmol/L 1 osmol/L
2 osmol/L in total
Example 2:
A 1 M CaCl2 solution contains 3 osmol of solute per liter of
solution.
CaCl2 → Ca 2+ + 2 Cl1 M does dissociate 1 osmol/L 2 osmol/L
3 osmol/L in total
Example 3:
The concentration of a 1 M glucose solution is 1 osmol/L.
C6H12O6 → C6H12O6
1 M does not dissociate → 1 osmol/L


? osmolarity of 0,15 mol/l of these solutions
◦
◦
◦
◦
NaCl
MgCl2
Na2HPO4
glukózy
0,30
0,45
0,45
0,15
osmol/l
osmol/l
osmol/l
osmol/l
Saline is 150 mM solution of NaCl. Which solutions are
isotonic with saline?
◦
◦
◦
◦
300 mM glukóza
50 mM CaCl2
300 mM KCl
0,15 M NaH2PO4
300 mosmol/l
300 mosmol/l
150 mosmol/l
600 mosmol/l
300 mosmol/l

Generally expressed as part of solute per 100 parts of
total solution (percent or „per one hundred“)

Three basic forms:
1) weight per unit weight (W/W) g/g of solution


10% NaOH → 10g of NaOH+90g of H2O = 100g of sol.
10% KCl → 10g of KCl/100g of solution
2) volume per unit volume
(V/V) ml/100ml of solution

5% HCl = 5ml of HCl / 100ml of sol.
3) weight per unit volume
(W/V) g/100 ml (g/dl; mg/dl; μg/dl; g % )


The most frequently used expression in medicine
20% KOH = 20g of KOH / 100 ml of sol.

conversion of molar concentration to percent
concentration
c  1000
 g / cm 3 
M g / mol 
w

How many grams of NaCl and how mL H2O need to
prepare 600 g of 5% NaCl solution? 30gNaCl, 570 g H O
2
How many grams of Na2CO3 at 96% purity needed
to prepare 250 g of 8% solution of Na2CO3? 20,83g
How ml ethanol and how mL H2O need to prepare
250 ml 39% ethanol?
97,5ml EtOH, 152,5 ml H2O
Fabric concentration physiological saline (NaCl) is
150 mM. What is the percent concentration? Mr =
58.5, density is 1g/cm3.
0,9%


pmol/L ‹ nmol/L ‹ mol/L ‹ mmol/L ‹ mol/L
10-12

10-6
10-3
g ‹ mg ‹ g
10-6

10-9
10-3
g
L ‹ mL ‹ dL ‹ L
10-6
10-3
10-1
L
1L = 1dm3
1mL = 1 cm3
mol/L