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OPRA Pharmacokinetics and Pharmacodynamics QUESTION #3849
Question 1
Given $\text{Na}\ M_r = 23$ and $\text{Cl}\ M_r = 35$, what is the sodium ion concentration of a $0.9\%\ \text{w/v}$ sodium chloride solution?
  • $100\ \text{mmol/L}$
  • $130\ \text{mmol/L}$
  • $150\ \text{mmol/L}$✔️
  • $270\ \text{mmol/L}$
Correct Answer Explanation
$0.9\%\ \text{NaCl} = 9\ \text{g/L}$. $M_r$ of NaCl $= 23 + 35 = 58\ \text{g/mol}$. Moles $= \dfrac{9}{58} = 0.1552\ \text{mol/L} \approx 155\ \text{mmol/L} \approx 150\ \text{mmol/L}$.