To convert a percentage concentration to mg/mL, you need to know that a percentage (denoted as 'w/v') means grams of solute per 100 mL of solution.
A 56% (w/v) solution means there are 56 grams of solute in 100 mL of solution.
To convert grams to milligrams (mg), recall that 1 gram = 1000 milligrams.
Thus, 56 grams = 56,000 mg.
Now, since this amount is in 100 mL:
\[ \text{Concentration in mg/mL} = \frac{56000 \text{ mg}}{100 \text{ mL}} = 560 \text{ mg/mL} \]
Therefore, 56% is equivalent to 560 mg/mL.