Back to Questions
OPRA Medicinal Chemistry and Biopharmaceutics QUESTION #3821
Question 1
How many grams of ingredient A are required to prepare $500$ mL of a stock solution, from which $25$ mL diluted to $100$ mL yields a $1{:}2000$ (w/v) solution?
  • $0.1$ g
  • $1$ g✔️
  • $1.25$ g
  • $2.5$ g
Correct Answer Explanation
Final concentration $= \dfrac{1}{2000} = 0.05\%\ \text{w/v}$. In $100$ mL $= 0.05$ g. In $25$ mL of stock: $0.05$ g. Stock concentration $= \dfrac{0.05}{25} \times 100 = 0.2\%\ \text{w/v}$. In $500$ mL stock: $\dfrac{0.2 \times 500}{100} = 1\ \text{g}$.