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microsoftinternetexplorer4
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 .
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 na2co3solution
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 na2co3solution
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 ?
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:-
q / prepare 2n solution in 250 ml volumetric
flask from 5n of hcl stock solution .
q / prepare 500 ml , 5n h2so4solution from original concentrated solution. .
preparation of 0.1 m na2co3solution 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.
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.
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 |
ph |
ml of solution a |
ml of solution b |
|
1 |
4.2 |
5.86 |
4.14 |
|
2 |
4.4 |
5.59 |
4.41 |
|
3 |
4.6 |
5.33 |
4.68 |
|
4 |
4.8 |
5.07 |
4.93 |
|
5 |
5 |
4.85 |
5.15 |
|
6 |
5.2 |
4.64 |
5.36 |
|
7 |
5.4 |
4.43 |
5.58 |
|
8 |
5.6 |
4.2 |
5.8 |
|
9 |
5.8 |
3.96 |
6.03 |
|
10 |
6.0 |
3.69 |
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 dropings 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 dropings 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 dropings 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