Inorganic qualitative analysis of radicals of elements Na, K, Ca, Ag, Mn, Fe, Co, Mg, Al, Cu and acid radicals: CO3, halides, citrates, SO4, SO3, NO3, etc.

2. Inorganic pharmaceutical chemistry Lab II
Arranged by- Md. Imran Nur Mnaik; B.Pharm.; M.Pharm.; RU Page 1
Inorganic pharmaceutical chemistry Lab II
Name of the Experiment: Determination of solubility of Benzoic acid, Salicylic acid, Citric
acid, Sodium Benzoate, Sodium Salicylate and Sodium Citrate in water, Boiling water and
alcohol.
Theory:
According to the USP the solubility is defined as “the number of milliliters of solvent
required to dissolve 1g of the solute”.
To understand the extent of the solubility of a substance USP has proposed following table-
Descriptive term Parts of solvent required to dissolve 1 part of solvent
Very soluble <1
Freely soluble 1-10
Soluble 10-30
Sparingly soluble 30-100
Slightly soluble 100-1,000
Very slightly soluble 1,000-10,000
Practically insoluble >10,000
So our target is to understand exactly under which category the substance fall under in
the respective solvent.
Apparatus:
i. Beakers
ii. Stirring rods
iii. Pipettes (1mL, 2mL, 5mL and 10mL).
iv. Bunsen burner
Chemicals:
1. Benzoic acid 2. Salicylic acid 3. Citric acid
4. Na-Benzoate 5. Na-Salicylate 6. Na-Citrate
7. Distilled water
8. Boiled water
9. Alcohol
COOH
COOH
OH
HOOC
H2
C C
H2
C COOH
COOH
OH
COO Na
COO Na
OH
Na OOC
H2
C C
H2
C COO Na
COO Na
OH
Md.
Imran
Nur
Manik

3. Inorganic pharmaceutical chemistry Lab II
Arranged by- Md. Imran Nur Mnaik; B.Pharm.; M.Pharm.; RU Page 2
Procedure:
There are four different pipettes (1mL, 2mL, 5mL, and 10mL). Using these 4 pipettes up
to 0.01mL, 0.01mL, 0.1mL, and 0.1mL can be measured accurately respectively.
i. First the 1g of the substance whose solubility is to be determined was taken in the
beaker by accurate weighing.
ii. The solvent was added in very small amount (say 0.1mL) using the pipette.
iii. Then using the glass rod it was stirred. The dissolution of the substance in the solvent
was observed.
iv. If it appears that the substance will not dissolve anytime soon then the amount of
solvent to be added can be increased. For example in place of 0.1mL, take 0.2 or
0.5mL to speed up the process.
v. But if considerable dissolution is observed the first time than the solvent should
added in small volume to obtain more accurate result.
vi. The total volume required to dissolve the solvent was noted.
vii. If the substance didn’t dissolve after addition of 35mL, then further testing was
abandoned and was termed “insoluble after 35mL”.
Result:
Chemical Solvent
Normal water/cool water Boiling water/hot water Alcohol
Amount
added (mL)
Decisio
n on
the
solubilit
y
Amount added
(mL)
Decision
on the
solubility
Amount
added (mL)
Decision
on the
solubility
Benzoic
acid
(Normal
amount is
~344 mL at
20⁰C)
(Slightl
y
soluble)
(Normal
amount is
~14mL)
(Soluble)
(Normally
~3mL is
required
when pure
ethanol is
used. For
10%ethanol
the amount is
~221 mL)
(Freely
soluble)
Salicylic
acid
(Normal
amount is
~500mL at
20⁰C)
(Slightl
y
soluble)
(one source says
that amount
required in
~1.3mL,
another says
that it is
~15mL)
(Freely
soluble
or
Soluble)
(Normally
3.5mL)
(Freely
soluble)
Md.
Imran
Nur
Manik

4. Inorganic pharmaceutical chemistry Lab II
Arranged by- Md. Imran Nur Mnaik; B.Pharm.; M.Pharm.; RU Page 3
Chemical Solvent
Normal water/cool water Boiling water/hot water Alcohol
Citric
acid
(Normally
~1.4mL at
20⁰C, about
0.5mL is
required)
(Very
soluble-
Freely
soluble)
? ?
(Normally
~3mL)
(Freely
soluble)
Sodium
benzoate
(Normally
1.6 (0r 1.8)
mL at 15-
30⁰C)
(Freely
soluble)
(Normally
1.4mL)
(Freely
soluble)
(75mL at
95% alcohol
and 50mL at
90% alcohol)
(Sparingly
soluble)
Sodium
salicylate
(Freely
but
slowly
soluble)
(Very
soluble)
(Freely
but
slowly
soluble)
Sodium
citrate
(Normally
1.5mL at
25⁰C)
(Freely
soluble)
(Normally
0.6mL at
100⁰C)
(Very
soluble)
(Practicall
y
insoluble)
Result:
Solubility in water: Citric acid > Salicylic acid > Benzoic acid
Solubility in water: Citrate > Salicylate > Benzoate
Solubility in alcohol: Citric acid > Benzoic acid > Salicylic acid
Solubility in alcohol: Salicylate > Benzoate > Citrate
Caution:
While stirring special care should be taken so that no solute adhere to the stirring rod or
the beaker at the upper portion. It is really difficult to dissolve this portion and always interfere
with the actual value.
Md.
Imran
Nur
Manik

5. Inorganic pharmaceutical chemistry Lab II
Arranged by- Md. Imran Nur Mnaik; B.Pharm.; M.Pharm.; RU Page 4
Name of the experiment: Identification of cations Na+
, K+
, Ca++
, Mg++
, and Fe.
Principle:
For the identification of cations there are two types of tests.
- Dry tests
- Wet tests
The dry tests include flame test, heat test, charcoal block test etc. most of these tests
usually don’t absolutely identify a cation and used for obtaining an idea of the cation. Wet test
is performed to confirm the presence of a cation.
But for Na+
, K+
there is no specific wet test and flame test is enough to properly identify them.
Following is a table describing the changes in the flame
Name of the cation Color in oxidized flame Color under blue glass
Na+
K+
Ca++
Mg++
Fe++
& Fe+++
Apparatus:
i. Beaker
ii. Pipette
iii. Test tubes
iv. Bunsen burner
v. Blue glass
vi. Filter paper
Reagents:
Method:
Tests for Na+
:
Flame test
The platinum wire is wetted by HCl acid and heated by the
flame of the Bunsen burner. Then it is soaked in HCl again and
touched to the sample to get small amount of the salt in the wire. Then
the wire is heated directly at the oxidizing flame of the burner and the
color is observed.
Through naked eye: Golden yellow
Through blue glass: Colorless (why it is colorless? Ans: Sodium is
present as impurities in almost all salts. Thus it shows yellow color.
thus blue glass is used to filter out the yellow flame).
Md.
Imran
Nur
Manik

6. Inorganic pharmaceutical chemistry Lab II
Arranged by- Md. Imran Nur Mnaik; B.Pharm.; M.Pharm.; RU Page 5
Wet test
There is no simple reagent that will precipitate sodium ions. But
when after neutralizing the sodium salt solution, potassium
pyroantimoniate is added and the inside of the test tube is rubbed using
a glass rod, precipitate forms.
Tests for K+
:
Flame test
Same procedure. The view through the blue glass is specially
important as there may be Na+
as impurity causing a yellowish flare;
but through blue glass the spectrum for potassium should be obtained.
Through the naked eye: Violet/purple/lilac
Through blue glass: Crimson
Wet test
There is no simple reagent that will precipitate the K+
from
solution. Sodium hydrogen tartrate can be used and the inside of the
test tube is rubbed using a glass rod to give ppt.
Tests for Ca++
:
Flame test
Same procedure.
Through the naked eye: brick red (actually red is bright
but intense)
Through blue glass: Light green
Wet test
First add ammonium hydroxide to turn the solution basic
(ammonium chloride may also be added). Then add ammonium
oxalate. A white precipitate is formed. This ppt. doesn’t dissolve in
acetic acid. This indicates the salts which are water soluble.
Another part of the sample is dissolved in dil. HCl. Then
ammonium oxalate is added to the filtrate. White ppt. of calcium
oxalate is observed. This indicates acid soluble salts.
Md.
Imran
Nur
Manik

7. Inorganic pharmaceutical chemistry Lab II
Arranged by- Md. Imran Nur Mnaik; B.Pharm.; M.Pharm.; RU Page 6
Tests for Mg++
:
Flame test
Same procedure.
Through naked eye: Bright white
Magnesium salts are coated with MgO. When the magnesium reacts
violently with air and magnesium fire is a problem. So this is not usually done.
Some magnesium salts don’t produce any flame color (colorless).
Wet test
1. Dissolve in water.
2. Filter to remove the impurities (e.g. talc. It has the formula
Mg3Si4O10(OH)2. It is insoluble in water and used as topical agent.)
3. perform following test
a. Add 6M NaOH (in 5:1 ratio). When excess of reagent is present a
precipitate of Mg(OH)2 will be formed. Using magnesium reagent
(p-nitrophenylazo resorcinol) will give a blue lake.
b. Add NH4Cl (1gm) + NH4OH (1gm) + Na2HPO4 (1gm) to filtrate
(25% solution). A white ppt. is formed.
Tests for Fe++
:
Flame test
Same procedure.
Through naked eye: Gold
Wet test
The sample is dissolved in water and filtered to remove the impurities. The
filtrate was divided to three parts and following tests were performed.
1. Filtrate + K4[Fe(CN)6] (potassium ferrocyanide). White or blue (actually
bluish) ppt. is observed.
2. Filtrate + K3[Fe(CN)6]. Intense blue colored solution was observed.
3. Filtrate + NH4CNS. No change.
Tests for Fe+++
:
Flame test
Same procedure.
Through naked eye: Gold
Wet test
The sample is dissolved in water and filtered to remove the impurities. The
filtrate was divided to three parts and following tests were performed.
4. Filtrate + K4[Fe(CN)6] (potassium ferrocyanide). Intense blue solution is
observed.
5. Filtrate + K3[Fe(CN)6]. Brownish solution was observed.
Filtrate + NH4CNS. Blood red solution was observed.
Md.
Imran
Nur
Manik

8. Md.
Imran
Nur
Manik

9. Md.
Imran
Nur
Manik

10. Md.
Imran
Nur
Manik

11. Md.
Imran
Nur
Manik