Pharmaceutical Chemistry is a key subject in D. Pharmacy, and understanding different drug and there chemical structures are clearly more important than just memorizing. In this post, Pharmaceutical Chemistry Important questions are explained in simple language, which is useful for MSBTE, AKTU, BTEUP, RUHS and other state boards.
Q1. What is Accuracy, Precision, and Significant Figures
Accuracy refers to how close a measured value is to the true or actual value. For example, if a standard solution contains exactly 10 ml of a drug and our measurement reads 10.01 ml, it is highly accurate.
Precision is about consistency: it shows how close repeated measurements of the same sample are to each other under the same conditions. You could be precise without being accurate if all your measurements are consistently off from the true value.
Significant Figures are the digits in a measurement that reflect both certainty and one estimated digit. They show the degree of reliability in reporting results. In pharmaceutical analysis, accuracy ensures that the amount of drug reported is true, precision shows reproducibility of the method, and significant figures help communicate results correctly without exaggeration.
Q2. Let’s learn about Impurities
An impurity is any unwanted substance present in a pharmaceutical material. Impurities can be toxic or non-toxic, and controlling them is critical for drug safety.
Below are the common sources of impurities
a) Raw materials where metals like arsenic or lead may already exist can cause impurity
b) Manufacturing process which can introduce contaminants
c) Equipment, where reactions between chemicals and vessels (iron, copper, aluminum) occur.
d) Solvents, especially if water or other reagents are not pure
e) Adulteration, where cheaper substances are mixed in deliberately
f) Improper storage, which causes decomposition
g) Atmospheric contamination, such as dust or pollutants entering the product.
Identifying and controlling impurities ensures that drugs remain safe, effective, and meet regulatory standards.
Q3. Limit Tests is also very important topic for every annual exam and semesters
Limit tests are qualitative or semi-quantitative tests that check whether certain substances are within acceptable limits in pharmaceutical products.
a) Limit Test for Chlorides: Chlorides react with silver nitrate in acidic medium to produce silver chloride, which appears as opalescence. The test solution is compared to a standard prepared with sodium chloride; the opalescence should not exceed the standard.
b) Limit Test for Sulphates: Sulphates react with barium chloride in acidic conditions to form a white precipitate of barium sulphate. The turbidity of the test solution is compared to a standard prepared with potassium sulphate; it should not exceed the standard.
c) Limit Test for Iron: Iron forms a reddish-violet complex with thioglycolic acid in ammoniacal medium. The color intensity of the test solution should not exceed the standard iron solution.
d) Limit Test for Heavy Metals: Heavy metals react with hydrogen sulphide in acidic medium to form coloured metal sulphides. The color produced in the test solution should not be darker than the standard (commonly a lead solution).
These tests are essential for ensuring drugs are safe and free from excessive impurities.
Q4. Limit Test for Arsenic Also known as Gutzeit Method is also very important topic for exam
The Gutzeit Method detects arsenic in pharmaceutical materials.
Arsenic is converted to arsine gas, which reacts with mercuric chloride paper to produce a yellowish-brown stain.
The intensity of the stain indicates the amount of arsenic present. The apparatus includes a wide-mouth bottle, rubber bung with glass tube, mercuric chloride paper, glass tube, and cotton plug.
The sample is treated with reagents to generate arsine gas, which reacts with the paper; the stain is then compared to a standard.
This method is simple, reliable, and widely used for safety testing.
Q5. Another important topic: Volumetric Analysis
Volumetric Analysis, also called titration, is a quantitative method where the volume of a reagent required to react completely with an analyte is measured. The analyte has an unknown concentration, while the titrant is of known strength. An indicator signals the endpoint by a colour change, and the volume of titrant used allows calculation of the analyte concentration. Reactions follow stoichiometric principles.
Types of volumetric analysis: Acid–base titration, Non-aqueous titration, Precipitation titration, Complexometric titration, Redox titration.
Volumetric analysis is widely applied in pharmaceutical labs for accurate drug assay, quality control, and standardization of solutions.
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