1) WHAT IS THE DIFFERENCE
BETWEEN WATER CONTENT & LOD?
Water content:
The amount of water present in the analyte in any form (including hydrated molecules)
Loss on drying:
The amount of volatile substances present in the analyte (all volatile solvents present including water).
Note:
In water content we determine only water. And in LOD we can determine water (except hydrated molecule) and organic volatile solvents present in the analyte.
2) WHAT IS THE DIFFERENCE BETWEEN LOD UNDER DRYING & LOD UNDER VACUUM?
In water content we determine only water. And in LOD we can determine water (except hydrated molecule) and organic volatile solvents present in the analyte.
2) WHAT IS THE DIFFERENCE BETWEEN LOD UNDER DRYING & LOD UNDER VACUUM?
Both are used for the
same purpose of determining the percent of water & organic solvents present
in the sample by vaporizing them.
LOD under Drying:
In this we dry the sample at a temperature of more than the water boiling range. Generally we use 105°C because water boiling point is 100°C and most of the solvents have the boiling point lower than 100°C.
This method is suitable only when our sample melting point is more than 100°C.If our sample melting point is less than 100° we cannot determine the water or any solvents having the boiling point less than the drying temperature
In this we dry the sample at a temperature of more than the water boiling range. Generally we use 105°C because water boiling point is 100°C and most of the solvents have the boiling point lower than 100°C.
This method is suitable only when our sample melting point is more than 100°C.If our sample melting point is less than 100° we cannot determine the water or any solvents having the boiling point less than the drying temperature
LOD under Vacuum:
If our sample has the lower melting range (less than 100°C) like 70°C (or) 85°C ...etc, We cannot vaporize the water or any solvent more than the drying temperature. In this case we use somewhat less temperature than the sample (If we use high temperature sample melts) for drying by applying proper vacuum to absorb the water or solvents present in the sample.
The main difference of both the methods is when sample have high melting range (more than 100°C) we can determine LOD by drying and when sample have low melting range (less than 100°C) we can determine LOD by drying under vacuum.
If our sample has the lower melting range (less than 100°C) like 70°C (or) 85°C ...etc, We cannot vaporize the water or any solvent more than the drying temperature. In this case we use somewhat less temperature than the sample (If we use high temperature sample melts) for drying by applying proper vacuum to absorb the water or solvents present in the sample.
The main difference of both the methods is when sample have high melting range (more than 100°C) we can determine LOD by drying and when sample have low melting range (less than 100°C) we can determine LOD by drying under vacuum.
3) HOW TO PREPARE 0.0002
mg/ml SOLUTION.BY USING 100 ml VOLUMETRIC FLASK FOR STOCK, 25 ml FOR
I st DILUTION AND 10 ml FOR SECOUND DILUTION? (Should take minimum 0.1 ml
for dilution).
Stock:
Dissolve 100 mg sample in 100 ml
Ist dilution:
Take 0.5 ml of stock in 25 ml volumetric flask and dilute up to
mark.
IInd dilution:
Take 0.1 ml of above Ist dilution in 10 ml v.f and dilute up to
mark.
Calculation:
= (100/100)
(0.5/25) (0.1/10) mg/ml
= 0.0002 mg/ml
4) HOW TO PREPARE 10ppm SOLUTION FROM 25% AMMONIA SOLUTION?
First convert ppm to % => 10 ppm = 0.001% (10/10000)
Apply C1V1=C2V2 Formulae
(25) (V1) = (0.001) (100)
V1
= 0.004 ml
So if we dilute 0.004 ml (4 µl) of 25% ammonia solution to 100
ml of water then we get 0.001%(10 ppm) solution.
Note:
1. If we have no syringe of 4µl how to dilute?
0.004ml to 100ml => 0.00004 ml to ml
Dilute 0.4ml to 100ml first and then 1ml to 100ml
(0.4/100)(1/100) = 0.00004ml to ml
5) WHAT IS PRIMARY STANDARD & SECONDARY STANDARD?
Primary standard:
A standard which is capable to prepare a known concentration of solution
by direct dissolving of a standard and diluting to an accurately
known volume of volumetric flask is called primary standard.
Requirements of a Primary standard:
- It should be available in a
pure form or in a state of known purity. In general total amount of
impurities should not exceed 0.01 to 0.02%, and it should be possible to
test for impurities by qualitative tests by known sensitivity.
- The substance should be easy to
dry and should not be hygroscopic that it takes up water during weighing
and should not efflorescence that it spontaneously loses water molecule to
the atmosphere. It should not lose weight on exposure to air.
- Primary standards should have high equivalent weight in order
to minimize the errors in weighing.
- It is preferable that the acid
or base be strong that is highly dissociated. However a weak acid or base
may be employed as a primary standard with no great disadvantages.
- It should be stable, non-toxic
and eco-friendly.
Note:
Eco-friendliness is environmentally
friendly means it should not affect the surrounding environment.
Examples:
1. Potassium hydrogen phalate (PHP) for
standardization of aqueous base (Like NaOH) and HClO4 in CH3COOH
solutions.
2. Na2CO3 for standardization of aqueous acids like HCl, H2SO4 and HNO3 solutions (but not CH3COOH).
3. NaCl for standardization of AgNO3 solutions.
4. Zn powder, after being dissolved in H2S04 or HCl, for standardization of EDTA solutions.
2. Na2CO3 for standardization of aqueous acids like HCl, H2SO4 and HNO3 solutions (but not CH3COOH).
3. NaCl for standardization of AgNO3 solutions.
4. Zn powder, after being dissolved in H2S04 or HCl, for standardization of EDTA solutions.
And also Arsenic trioxide, Periodate Benzoic acid, Potassium hydroxide, Potassium
bromate, Sufanilic acid ....etc
Secondary standard:
A solution standardized by titrating with a primary standard itself is a secondary standard
Secondary standard:
A solution standardized by titrating with a primary standard itself is a secondary standard
Examples:
NaOH, HClO4, HCl, EDTA, AgNO3, H2SO4, HNO3 ....etc.
NaOH, HClO4, HCl, EDTA, AgNO3, H2SO4, HNO3 ....etc.
6) WHAT ARE USP-1 AND USP-2 METHODS IN TAPPED
DENSITY APPARATUS, EXPLAIN?
Both used for the same purpose of determining
the density of analyte. But these have the difference in tapping height and
tapping count per minute.
USP-1:
Tapping height = 14±2 mm
Drops per min = 300 drops/min
USP-2:
Tapping height = 3 (±10%) mm
Drops per min = 250 drops/min
7)WHAT IS THE DIFFERENCE BETWEEN BULK DENSITY
AND TAPPED DENSITY?
Bulk
density:
It is the ratio of mass an
untapped powder sample to its volume, including contribution of
interparticulate void volume. Hence it depends on both the density of powder
sample and spatial arrangement of particles in the powder bed.
Tapped
density:
It is the ratio of mass after specified
tapping’s of a powder sample to its volume.
8)
CAN YOU EXPLAIN NON-AQUEOUS PERCHLORIC ACID TITRATION? (or)
HOW PERCHLORIC ACID REACTS WITH ACETIC ACID IN
PERCHLORIC ACID TITRATION?
Generally we use non-aqueous titration for
determination of weak bases. That is we dissolve our sample (weak base) in
acetic acid and titrate with perchloric acid.
As we all know perchloric acid is
strongest acid and acetic acid is weak acid. As we start titration, in presence
of a strongest perchloric acid weak acetic acid behaves like a base. That means
In the first step, a proton (H+)
is transferred from strongest perchloric acid to acetic acid (Which behaves
like base). (Known as leveling effect)
HCLO4 +
CH3COOH à CH3COOH2+
+ CLO4-
When a weak base dissolved in acetic acid,
the acetic acid exerts its leveling effect and enhances the basic properties of
the weak base. So to titrate a solution of weak base in acetic acid with
perchloric acid in acetic acid and obtained a sharp end point.
Let us take our
weak base is C5H5N
CH3COOH + C5H5N à C5H5NH+
+ CH3COO-
CH3COO-
+ CH3COOH2+ à 2 CH3COOH
By adding above
three equations
HCLO4 +
CH3COOH à CH3COOH2+ + CLO4-
HCLO4 + +
C5H5N à C5H5NH+
+ CLO4-
Note:
1.
In the first step acetic acid behaves as base and in the
next step same acetic acid behaves as acid.
9) WHY WE USE ONLY SULPHURIC ACID BUT
NOT NITRIC ACID or ANY OTHER IN SULPHATED ASH OR RESIDUE ON IGNITION TEST?
The purpose of
this test is to determine the inorganic content in given sample. By adding
H2SO4, we convert the inorganic to their sulphate derivatives in the given
sample. The inorganic sulphates are very stable even at high temperatures up to
1000°c. So we can easily estimate the inorganic content present in the given
sample by ignition.
If we use HNO3,
inorganic converts to their nitrate derivatives and if we use HCL they convert
to chloride derivatives which are not stable at high temperatures.
