Which factor is most important when calculating the Normality of HCl?

AIIMS CRE, SNO-2024

Biochemistry and Nutrition

Easy

Appeared in: AIIMS CRE, SNO-2024

Explanation

To calculate the concentration (Normality) of a stock solution like HCl, its percentage purity is a required parameter.
Commercial acids are not 100% pure, and the % purity value (assay) provided by the manufacturer indicates the actual amount of acid in the solution.
The formula for calculating Normality, N = (Specific Gravity × % Purity × 10) / Equivalent Weight, directly uses the % purity value.
Without knowing the % purity, it is impossible to determine the exact mass of the solute (HCl) and therefore impossible to calculate the true concentration.

Option A: Boiling point is a physical property related to the phase transition from liquid to gas. It does not provide information about the amount of solute in a solution and is not used in concentration calculations.
Option C: Viscosity measures a fluid's resistance to flow. While concentration can influence viscosity, it is not a parameter used for the precise calculation of Normality.
Option D: Pure HCl is a colorless solution. Color intensity is used in colorimetric analysis for substances that absorb light, but it is not applicable here and is not a fundamental property for calculating concentration from a stock solution.

Visual 1: Diagram - A flowchart illustrating the steps to calculate Normality from a stock acid, showing how Specific Gravity, % Purity, and Molecular Weight are used.
Visual 2: Image - A picture of a chemical reagent bottle (e.g., concentrated HCl) with the label clearly showing the % purity (assay), specific gravity, and molecular weight.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Calculation of Normality for a chemical solution (HCl) as background academic context rather than a clinical decision trigger.
Accurate preparation of solutions is fundamental in clinical and laboratory settings. Incorrect concentrations can lead to erroneous lab results, ineffective disinfection, or harm to patients.
For example, preparing a specific concentration of a disinfectant requires using the correct % purity of the stock solution to ensure it is effective at killing pathogens.
What if the nurse uses a new bottle of HCl from a different manufacturer? They must re-calculate the required volume based on the specific % purity and specific gravity listed on the new bottle's label, as these values can vary between batches and manufacturers.

How to Approach the Question

First, identify the core concept of the question, which is the calculation of 'Normality', a measure of chemical concentration.
Recall or look up the formula for calculating Normality from a concentrated liquid: Normality = (Specific Gravity × % Purity × 10) / Equivalent Weight.
Analyze the components of the formula. Notice that '% purity' is a direct and necessary variable.
Evaluate the given options in the context of this formula.
Recognize that '% purity' is in the formula, making it essential for the calculation.
Dismiss the other options (Boiling point, Viscosity, Color intensity) as they are physical properties not directly used in this standard concentration calculation.

Concept Tested & Keywords

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