JNTU B.Pharmacy II PHARMACEUTICAL ANALYSIS-I Previous Question Paper (September-2021 - R17)

Sodium hydroxide (NaOH) is a secondary standard because it is hygroscopic and absorbs carbon dioxide from the atmosphere. Therefore, it must be standardized against a primary standard like potassium hydrogen phthalate (KHP).

Preparation: To prepare 1L of 1N NaOH, dissolve 40g of NaOH pellets in approximately 500mL of carbon dioxide-free distilled water. Once dissolved and cooled, dilute the solution to 1000mL with carbon dioxide-free water and store it in a polyethylene bottle to prevent leaching of silicates from glass.

Standardization:

1. Accurately weigh about 5g of dried primary standard KHP and dissolve it in 75mL of carbon dioxide-free water.
2. Titrate this solution with the prepared NaOH solution using phenolphthalein as an indicator until a faint permanent pink color appears.
3. Calculate the exact normality (N) using the formula: N = (Weight of KHP in mg) / (Equivalent weight of KHP × Volume of NaOH in mL). The equivalent weight of KHP is 204.22.

Errors in pharmaceutical analysis represent the difference between the measured value and the true value. They are broadly classified into three types:

1. Determinate (Systematic) Errors: These are errors with a definite cause and a unidirectional bias, meaning they can be identified and corrected. They include:

• Operational errors: Caused by the analyst's lack of technique (e.g., loss of sample during transfer).
• Methodic errors: Inherent to the analytical method (e.g., incomplete reaction or incorrect indicator choice).
• Instrumental errors: Caused by faulty equipment (e.g., uncalibrated burettes or balances).

2. Indeterminate (Random) Errors: These arise from uncontrollable variables such as slight fluctuations in temperature, humidity, or minor variations in reading a meniscus. They follow a normal distribution (Gaussian curve) and cannot be eliminated, but their impact is minimized by taking multiple readings and calculating the mean.

3. Gross Errors: These result from human negligence or accidents, such as misreading a scale, spilling a sample, or using the wrong reagent. These errors are large and usually necessitate discarding the entire set of results and repeating the experiment.