Concentration units
1-Normality of solution:Is defined as the number of grams-equivalent weight of solute per one liter of solution .
Molarities of solution :A molar solution contains one gram molecular weights of solute dissolved in sufficient amount
of solvent to give 1 liter of solution .
X
=
M=
V (ml)
wt
gram molecular wt. of solute
volume of solvent (L)
MWT
1000
Formality :- is the number of grams formula weight of solute per liter of solution. used for
partial dissolved solutes (such as acetic acid , oxalic acid etc…)
Preparation of 1% w/v Na2CO3 solution
Weigh 1 gm of sodium carbonate using a watch glass, transfer it into a beaker, then add 50
ml. of distilled water(mix using a stirrer )transfer the solution into a volumetric flask of 100 ml.
add distilled water to the mark.
Mix the solution by inverting the flask 2-3 times to mix the component .
Q / prepare 0.3 % solution from 1% solution in 250 ml volumetric flask.
Preparation of 0.1N Na2CO3 solution
Weigh 1.325 gm of Na2CO3 (using a watch glass ) transfer it into a beaker. Add 100 ml of
distilled water (using a stirrer to mix), after dissolving , transfer the solution into a volumetric
flask of 250 ml then add water to the mark .
Q / From this solution prepare 0.05 N , and 0.02 N solution in 250 ml distill water ?
eq wt. x N X V (ml)
Wt. =
1000
To prepare dilute solution from stock solution , this law must be used :Dilution law is :- (N x V)1 = (N x V)2
Where (1) refer to the concentrated solution and (2) refer to the diluted solution.
To find the normality of concentrated solutions (for liquid only) this law must be used:-
density or spicific gravity x wt % x 1000
N=
eq.wt of solution
Or :
density or spicific gravity x wt % x 1000
M=
MWt. of solution
Q / prepare 2N solution in 250 ml volumetric flask from 5N of HCl stock solution .
Q / prepare 500 ml , 5N H2SO4 solution from original concentrated solution. .
Preparation of 0.1 M Na2CO3 solution in 250 ml D.W
Weight 2.65 gm of Na2CO3 , transfer it into a beaker. Add 100ml of D.W ( mix using a glass
stirrer ).Transfer the solution into a 250 ml volumetric flask of, add water to the mark.
ppm =
wt of solute x 10 6
wt of solution
ppm =
mg (solute)
10 6 mg water
mg (solute)
=
L (solution)
Wt (gram)
mole of solute =
Molecular weight (g / mole)
Molecular weight (g / mole)
eq.wt of solute =
no of H + In acids
no of OH - in base
no of cation charge in salts
So : 1M Na2CO3 = 2N Na2CO3
part per million (PPm )
The concentration of very diluted solutions ,It’s the number of mg of salt dissolved in one liter
solution.
ppm =
ppm =
wt of solute x 10 6
wt of solution
mg (solute)
10 6 mg water
=
mg (solute)
L (solution)
Buffer solution
Any solution that contains both a weak acid and it’s weak base, has the ability to absorb small
amounts of either a strong acid or strong base are added they are neutralized by the weak
base , while small quantities of a strong base are neutralized by the weak acid, such solution
are said to be buffer because they resist significant change in the PH .The PH value is
determined by a PH meter.
Using of indicators in a PH estimation:Principle:A set of buffer solution of known PH is prepared form citric acid and disodium monohydrogen
phosphate.
The color of the indicator in an unknown solution is compared with the color of indicator in
these buffer solution , assuming that the concentration of the indicator in all solution is the
same.
The buffer solution in which the color of the indicator is the same as color of the indicator in
the unknown solution has the same PH as this solution.
Procedure :Fill one burette with citric acid solution 0.1 molar and a second burette with 0.2 molar
disodium monohydrogen phosphate ( called solution A and B respectively) .
Use the following table in preparing a set of buffer solutions:No
1
2
3
4
5
6
7
8
9
10
PH
4.2
4.4
4.6
4.8
5
5.2
5.4
5.6
5.8
6.0
ml of solution A
5.86
5.59
5.33
5.07
4.85
4.64
4.43
4.2
3.96
3.69
ml of solution B
4.14
4.41
4.68
4.93
5.15
5.36
5.58
5.8
6.03
6.32
The way to work is follows:1- Label 10 test tube from 1 to 10 , into number 1 run 5.86 ml of solution A and 4.14 ml
of solution B , mix well, fill the other test tube in a similar way , using the volumes of A
and B mentioned in the table. In this way we obtain a set of buffer solution (10 ml of
each ) having a PH from 4.2 to 6.0
2- Use methyl red as an indicator ,add to each 10 ml buffer solution above, 5 drops of
the methyl red indicator solution .(PH rang 4.4 to 6.0 ),mix the contents of the tubes
well.
3- Bring into a test tube 10 ml of a 0.05 N ammonium chloride solution ,add 5 drops of
the indicator solution and mix .compare the color produced with the color in the test of
buffer solution.
4- Using a pipette bring into a flask 10 ml 0.1 N acetic acid solution and 10 ml 0.1 N
sodium acetate solution .mix then ,bring 10 ml of this buffer solution into test tubes
,add 5 drops indicator solution ,and make an estimation of PH of this buffer solution
as before.
Preparation of a buffer solution with PH = 4.6
Mix 5 ml of 0.2 M acetic acid with 5 ml of 0.2 M sodium acetate.(mix using a stirrer).
Preparation of a buffer solution with PH = 7
Mix 17 ml of 0.02 M Na2HPO4.2H2O with 3.9 ml of citric acid .
Preparation of a buffer solution with PH = 9.4
Mix 5 ml of NaOH , 0.1N with 16.6 ml of 0.15 M Na2HPO4.2H2O