Percentage of Na+ in 0.9% of NaC1 –
## **Core Concept**
The question tests understanding of the composition of a commonly used isotonic saline solution, specifically the concentration of sodium ions (Na+) in 0.9% sodium chloride (NaCl) solution. This solution is isotonic to human blood and is often used in medical settings for fluid resuscitation and as a vehicle for drug administration.
## **Why the Correct Answer is Right**
0.9% NaCl solution, also known as normal saline, contains 0.9 grams of NaCl per 100 mL of solution. The molecular weight of NaCl is approximately 58.44 g/mol, with Na+ having a molecular weight of about 23 g/mol. When NaCl dissolves, it completely dissociates into Na+ and Cl-. Therefore, the number of moles of Na+ ions will be equal to the number of moles of NaCl.
To calculate the molarity of 0.9% NaCl:
- 0.9 g of NaCl in 100 mL (or 0.1 L) of solution.
- Moles of NaCl = 0.9 g / 58.44 g/mol = 0.0154 mol
- Since NaCl gives 1 mole of Na+ per mole of NaCl, moles of Na+ = 0.0154 mol
- Molarity of Na+ = 0.0154 mol / 0.1 L = 0.154 M
The molar mass of Na+ is 23 g/mol.
- Mass of Na+ in 0.1 L = 0.0154 mol * 23 g/mol = 0.3542 g
In 1 L (1000 mL) of 0.9% NaCl:
- The mass of Na+ = 3.542 g
## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is incorrect because it does not accurately reflect the percentage of Na+ in 0.9% NaCl solution based on the calculation above.
- **Option B:** This option is incorrect for the same reason as Option A; the calculation does not support this value.
- **Option C:** This is the correct calculation: 0.9% of NaCl provides approximately 154 mEq/L of Na+, which translates to about 3.54 grams of Na+ per liter. When considering the contribution to the total milliequivalents or grams in the context of typical medical or physiological problems, this seems to align with a commonly referenced conversion.
## **Clinical Pearl / High-Yield Fact**
A key point to remember is that 0.9% NaCl solution is isotonic and provides approximately 154 mEq/L of sodium ions, which is close to the sodium concentration in human blood. This makes it an ideal solution for replacing fluids without significantly altering the osmotic balance of blood.
## **Correct Answer:** .