Answer:
Concentrations can be calculated in several different ways that all give different answers. The most common types of concentrations are by moles, mass, and volume. If this is really the entire question, I would have to assume they want the volume answer because we can't determine the mass or the moles of alcohol without knowing the actual formula of the alcohol. So this is how you do volume concentration:
concentration% = volume of pure substance / total volume of combination * 100
or
12% = .12(16)/16 * 100 (just a restatement of the given)
So starting with 16 ml of solution, we add x ml of water to get a total volume of (16+x). And the amount of pure alcohol is found from .12(16).
Now we calculate: 8% = .12(16)/(16+x) * 100 Solve for x.
.08 = 1.92/(16+x)
.08(16+x) = 1.92
16 + x = 1.92/.08 = 24
x = 24 - 16 = 8 ml
Explanation: