Question 1

What is the difference between accuracy and precision in analytical chemistry?

Accepted Answer

Accuracy refers to how close a measured value is to the true value, while precision indicates how reproducible repeated measurements are. In pharmaceutical analysis, both are critical: a method must be accurate to ensure correct drug dosage and precise to guarantee consistent results. For example, a balance may give precise readings (e.g., 1.000 g, 1.001 g) but be inaccurate if not calibrated (true mass = 1.050 g).

Question 2

How do I calculate the percentage yield of a reaction?

Accepted Answer

Percentage yield = (actual yield / theoretical yield) × 100%. First, determine the theoretical yield by calculating the moles of limiting reactant and using the stoichiometric ratio to find the maximum product mass. Then, divide the actual mass obtained from the experiment by this theoretical value and multiply by 100. A yield below 100% is common due to side reactions or losses; yields above 100% indicate impurities.

Question 3

What is the role of a buffer in pharmaceutical formulations?

Accepted Answer

A buffer resists changes in pH when small amounts of acid or base are added. In pharmaceuticals, buffers maintain the pH of a drug solution within a narrow range to ensure stability, solubility, and efficacy. For example, phosphate buffers are used in eye drops to keep pH close to that of tears (pH 7.4), preventing irritation and preserving the active ingredient.

Question 4

Why is stereochemistry important in drug design?

Accepted Answer

Stereochemistry refers to the three-dimensional arrangement of atoms in a molecule. Many drugs are chiral, meaning they exist as non-superimposable mirror images (enantiomers). Often, only one enantiomer is biologically active, while the other may be inactive or even toxic. For instance, the drug thalidomide had one enantiomer that caused birth defects, highlighting the need for stereochemically pure drugs.

Question 5

How does HPLC work in simple terms?

Accepted Answer

HPLC (High-Performance Liquid Chromatography) separates components of a mixture based on their polarity. The sample is dissolved in a mobile phase (liquid) and pumped through a column packed with a stationary phase (e.g., silica). Compounds interact differently with the stationary phase: polar compounds stick more and take longer to elute, while non-polar compounds pass through quickly. A detector measures each component as it exits, producing a chromatogram.

Question 6

What is the difference between an exothermic and endothermic reaction?

Accepted Answer

An exothermic reaction releases heat to the surroundings, resulting in a temperature increase (e.g., combustion). An endothermic reaction absorbs heat from the surroundings, causing a temperature decrease (e.g., photosynthesis). In pharmaceutical manufacturing, exothermic reactions require careful cooling to prevent runaway reactions, while endothermic reactions may need heating to proceed efficiently.

OCN NI Level 4 Certificate in Chemistry for the Pharmaceutical and Life Science Industries

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