Upload
syafiie-syukri
View
221
Download
2
Embed Size (px)
Citation preview
7/27/2019 Expression of concentration 8-7.ppt
1/36
http://www.m5zn.com/7/27/2019 Expression of concentration 8-7.ppt
2/36
Expression of concentration
ByProf. Dr/ Iman El-shabrawy
7/27/2019 Expression of concentration 8-7.ppt
3/36
ObjectivesAt the end of this lecture you should be able
to:-1- Describe various expressions of concentrations
used.2- Explain dilution, concentrated, saturated and
supersaturated solution.3- Explain biological solution concentration i.e
hypertonic, hypotonic and isotonic.4- Differentiate molarity, molality & normality of
solutions.5- List units of concentration used in medicine(g%, m.mol, mg/dl, etc.)
7/27/2019 Expression of concentration 8-7.ppt
4/36
Concentrations Concentration of a solution representsamount of solute dissolved in a givenamount of solvent or solution.
Concentration =Amount of solute
Amount of solution
7/27/2019 Expression of concentration 8-7.ppt
5/36
Ways of expressing concentration
1-QuantitativelyDilute solution : a solution thatcontains a small proportion of solute
relative to solvent.Concentrated solution: a solution thatcontains a largeproportion of solute
relative to solvent.To concentrate a solution, one must add moresolute, or reduce amount of solvent (e.g., byevaporation).
7/27/2019 Expression of concentration 8-7.ppt
6/36
These glasses containing red dye demonstratequantitative changes in concentration.
Dilution
By contrast, to dilute a solution, one mustadd more solvent, or reduce amount ofsolute.
http://en.wikipedia.org/wiki/Image:Dilution-concentration_simple_example.jpg7/27/2019 Expression of concentration 8-7.ppt
7/36
2-Semi-Quantitatively
Unsaturated solution : a solution in whichmore solute will dissolve.Saturated solution : a solution in which nomore solute will dissolve.
Supersaturation If additional solute is added to a saturated
solution, it will not dissolve (supersaturation
occur). So, a solution containing more solute over
saturated solutions is called supersaturated.
7/27/2019 Expression of concentration 8-7.ppt
8/36
Biological solution concentration
Hypertonic, isotonic & hypotonic Solutions Words hypertonic, isotonic and hypotonic
describe water conc. of 2 solutionsseparatedby a selectively permeable membrane such as
cell membrane. Hypertonic = solution with lower water conc.
(higher solute concentration)
Hypotonic = solution with higher water conc.(lower solute concentration)
Isotonic = 2 solutions with same water conc.
(equal in their solute concentrations)
7/27/2019 Expression of concentration 8-7.ppt
9/36
Solute will move from hypertonic
solution into hypotonic solution.
7/27/2019 Expression of concentration 8-7.ppt
10/36
3- Qualitatively Many ways, it is sometimes preferred to
measure volume rather than mass of a solution.
Some qualitative expressions for conc. aretemperature-dependent(i.e,conc of solutionchanges as temp. changes), whereas others are
not. Important for experiments in which temperature
does not remain constant.
7/27/2019 Expression of concentration 8-7.ppt
11/36
Concentrationexpression
Measurementsrequired
Temperaturedependence
Percent composition
(by mass)mass of solute
& mass ofsolution
No(mass does notchange with temp.)
Percent composition
(by volume) volume of solute& volume of
solution
yes(volume changes with
temp.)
percent composition
( mass/volume)mass of solute& volume of
solution
yes(volume changes with
temp.)
Qualitative expression of concentration
7/27/2019 Expression of concentration 8-7.ppt
12/36
molarity moles of solute&volume ofsolution
yes(volume changes with
temp.)
molality Moles of solute
&mass of solvent
no(neither mass normoles changes with
temp.)
mole fraction moles of solute
&moles of solvent
no
(moles do not changewith temp.)
Concentrationexpression
Measurementsrequired
Temperaturedependence
continuous
7/27/2019 Expression of concentration 8-7.ppt
13/36
Mole Mole(from molecule), with symbol = mol is
used to measure amount of a substance.
1 mole is amount of a substance which contains as
manyelementary unitsas there are atoms in0.012 Kg (12 gram).of C12 (Avogadro constant).
This measure tells us number of reactingparticles.
http://en.wikipedia.org/wiki/Avogadro_constanthttp://en.wikipedia.org/wiki/Avogadro_constant7/27/2019 Expression of concentration 8-7.ppt
14/36
Molarity (M) , of a solution is calculated by
taking moles of solute & dividing by liters ofsolution, hence
Molarity = moles / litre
In other words
Therefore
7/27/2019 Expression of concentration 8-7.ppt
15/36
Molar solution
Is a solution, which contains themolecular weight of solute in gramsdissolved in one liter of the solution.
Usually concentration is expressed as afraction of mole e.g.:-
Millimole (m M) = 1/1000 mole
Micromole ( M) = 1/1000,000 moleNanomole (nM) = 1/1000,ooo,ooo
7/27/2019 Expression of concentration 8-7.ppt
16/36
Remember!!!
Measurement in moles is a measurementof amount of a substance.Measurement in molarity is ameasurement of concentration of asubstance [amount (moles) / unit volume
(liters)].
http://www.m5zn.com/7/27/2019 Expression of concentration 8-7.ppt
17/36
Dilution of stock solutions Dilution of stock solutions is frequently used
to make solutions of any desired molarity.What does it mean to dilute a solution? Means to add more solvent without adding
more solute. The fact that solute amount stays constant
allows calculations to be made:
7/27/2019 Expression of concentration 8-7.ppt
18/36
Continuous
moles before dilution = moles after dilution (X)
From definition of molarity (above):
moles of solute = molarity * volume
So we can substitute MV (molarity * volume) intoequation (X) above:
Molarity 1 * Volume 1 = Molarity 2 * Volume 2
In short, M1V1 = M2V2
1 refers to the situation before dilutionand 2 refers to it after dilution.
7/27/2019 Expression of concentration 8-7.ppt
19/36
Example 1 :
You have 60 ml of a 1.5 M solution of
NaCl, but 0.6 M solution is needed. Howmany ml of 0.6 M can you make?
We know that, M1V1 = M2V2
1.5 M * 60 ml = 0.6 M * (V 2) V2= 150 ml
7/27/2019 Expression of concentration 8-7.ppt
20/36
Mole Fraction (X):- X, of a component is ratio of no.of moles of
that component to total no of moles of allcomponents in solution.To calculate mole fraction, we need to know:Number of moles of each component present in
the solution. if we need to know, mole fraction of A[XA] in
a solution consisting of A, B, C, ... iscalculated using the equation
7/27/2019 Expression of concentration 8-7.ppt
21/36
continuous
To calculate mole fraction of B, XB,
then
7/27/2019 Expression of concentration 8-7.ppt
22/36
The molality (m)Molality (m) , molality (m) molality (m)
(yes this is the right spelling) . Concentration measured as
moles of solute /kilogram of solvent(molality = moles / kilogram).
Molalities are preferred in experimentsthat involve temperature changes e.g.
calorimetry & freezing point depression.
7/27/2019 Expression of concentration 8-7.ppt
23/36
continuous
Therefore:-
A 1 m (not 1 M) NaCl solution contains 1 moleof NaCl /kilogram of water.
7/27/2019 Expression of concentration 8-7.ppt
24/36
Normality (N) Is number of equivalents of solute/ liter of
solution.
Equivalent weight equals molecular weight in
grams divided by valence. Normal solution is a solution which contains
equivalent weight of solute in grams dissolved in
1 liter of solution.
7/27/2019 Expression of concentration 8-7.ppt
25/36
continuous
For example, hydrogen has atomic weight 1.008& valence 1, has an equivalent weight of 1.008.
Oxygen has an atomic weight of 15.9994& avalence of 2, so it has an equivalent weight of7.9997.
Elements may assume different equivalentweights in different compounds.
For example, iron (atomic weight 55.845)assumes equivalent weight 27.9225 ,if it isvalence is 2 in the compound (ferrous Fe+2); or18.615 if it is valence 3 (ferric fe+3).
N B:
7/27/2019 Expression of concentration 8-7.ppt
26/36
N.B:
- Weight of a molecule is the sum of weights ofatoms of which it is made.
- Unit of weight is dalton (da) which equals 1/12of weight of an atom of C12.
- Thus (MW) of water is 18 daltons & glucose is
180 daltons.- Mole is quantity of a substance whose weight in
grams is equal to MW of substance.
- Thus 1 mole of glucose weight 180 g.
- Furthermore , if you dissolve 1 mole of asubstance in 1 liter (L) of water to make asolution , you have made a 1 molar (1M)
solution.
7/27/2019 Expression of concentration 8-7.ppt
27/36
continuous
- Molarity
M= number of moles (mol.w) of solution/Lof solution.
- Normality
N= number of equivalents of solution/ Lof solution.
- Molality
m= number of moles of solute/1000 g ofsolvent.
7/27/2019 Expression of concentration 8-7.ppt
28/36
Parts / million ( p p m) A unit of conc. often used when
measuring levels of pollutants in air,water, body fluids etc.
1p p m (1 part in 1000,000) is equal to
the common unit mg/liter.
7/27/2019 Expression of concentration 8-7.ppt
29/36
Some units of concentration used in medicine
milligrams / liter (mg/L), SI unit of conc.Parts / million is an older expression of mg/L,(since 1liter of water under standard conditions weights 1kilogram or 1 million milligrams).mg/Lis often used in medicine & prescriptions.Similarly milligrams / deciliter (mg/dl) ,m.mol &also g% are common medical unit.
Unit/ liter (U/L)Amount of enzyme that hydrolyse 1 m.mol ofsubstrate under optimal conditions.
7/27/2019 Expression of concentration 8-7.ppt
30/36
How to change from m.mol/L into mg/dl:
mg/dl= m. Mol / L X molecular weight10
How to change from mg/dl into m. mol:
m.mol/L= mg/dl X 10Molecular weight
Molecular weight= total atomic weight
7/27/2019 Expression of concentration 8-7.ppt
31/36
QuestionsMCQMeasurement in moles is a measurement of :-A- amount (moles) / unit volume (liters).B-number of equivalents of solution/ L of
solution.C-number of moles of solute/1000 g of solvent.D- amount of a substance.E- the substance weight in grams equal to its
molecular weight.D & E
7/27/2019 Expression of concentration 8-7.ppt
32/36
OBA
The molecular weight of glucose is 180 daltons.If you dissolve 180 grams of glucose in water,which of the following is the best descriptionfor the result of this process?
A. a solution of glucose in water.B. a homogenous mixture.
C. a 1 molar solution if water is 1 liter.
D. a hypertonic solution.E. a concentrated solution.
C
7/27/2019 Expression of concentration 8-7.ppt
33/36
Relational
Volume/volume % expression of concentrationis not used in temperature dependentexperiments.
BECAUSE
Volume/volume % is often used whenmeasuring levels of pollutants in air.
C
7/27/2019 Expression of concentration 8-7.ppt
34/36
How to prepare 1 molarity solution?
No of mol. wt of substance 1 L
How to prepare 1 normality solution?
No of equivalent wt. 1L
equivalent wt. =Mol .wtvalence
Q i
7/27/2019 Expression of concentration 8-7.ppt
35/36
QuestionYou need 225 ml of 0.8 M NaOH solution and
you have a 2.5 M stock solution. How would
you make up the solution?2.5 M * (V1) = 0.8 M * 225 mlV1 = 72 mlQuestion :
using M1V1 = M2V2 relationship, determinethe following;60 ml of a solution are diluted to a volume of120 ml. The concentration of the diluted
solution is 2 M. What was the concentrationof the original solution?
M1 = (2 * 0.12)/0.06 = 4 M120ml 60ml
7/27/2019 Expression of concentration 8-7.ppt
36/36