How much salt must be added in one litre of water to make a solution of normal saline (0.9%)?

Appeared in: IGNOU Post B. SC. Nursing entrance -2021

Explanation

The term '0.9%' w/v (weight by volume) signifies that there are 0.9 grams of solute for every 100 mL of the solution.
The question requires preparing 1 litre of solution, which is equivalent to 1000 mL.
To find the amount of salt needed for 1000 mL, a simple proportion is used: (0.9 g / 100 mL) = (x g / 1000 mL).
Solving for x gives 9 grams. (0.9 g * 10 = 9 g).

Option A: 19 gm is an arbitrary value and does not correspond to the calculation for a 0.9% solution.
Option B: 90 gm would create a 9% solution in 1 litre, which is a highly concentrated hypertonic solution and would be dangerous for most clinical uses.
Option C: 9 gm is the correct amount of salt for 100 mL of normal saline, not for 1 litre (1000 mL).

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Drug Calculation: Percentage Solutions as background academic context rather than a clinical decision trigger.
Accurate drug and solution calculation is a fundamental and critical nursing skill to ensure patient safety and prevent medication errors.
Normal saline (0.9% NaCl) is an isotonic crystalloid solution, meaning it has the same effective osmolality as body fluids. This makes it ideal for expanding extracellular fluid volume without causing major fluid shifts in cells.
It is commonly used for dehydration, hypovolemia, and as a flush for intravenous lines.

How to Approach the Question

First, identify the key components of the question: the desired concentration (0.9%) and the final volume (1 litre).
Recall or look up the definition of a percentage solution in a medical context: 'X%' means 'X grams per 100 mL'.
Convert all units to be consistent. In this case, convert 1 litre to 1000 mL.
Set up a ratio or proportion to solve for the unknown amount of salt. If 0.9 g is in 100 mL, how many grams (x) are in 1000 mL?
Calculate the final answer: x = (0.9 g / 100 mL) * 1000 mL.
Compare your calculated answer (9 g) with the given options to select the correct one.

Concept Tested & Keywords

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E6 Pharmacology Nursing Lilley 11e Part 2 p. 161-163

E6 Nursing Brunner Adult Health 3SA Vol 1 Part 1 p. 142-144

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