I have been reading trying to learn about this stuff. I Know that a ml(milliliter)= 1cc.
A milliliter is a measure of volume.
Why do people talk about a liquid substance in terms of mg(milligrams), a measure of mass? How many mg(milligrams) makes 1 cc or ml?
You don’t think an amount of liquid has a mass? Everything that is matter has mass (solid, liquid, gas, etc), otherwise, it wouldn’t be matter. mL doesn’t convert to mg; volume and mass are different quantities. Volume is the amount of space something occupies. Mass, in laymen’s terms, is the “amount of matter” in the object. If you want find the mass of a given volume of liquid, you need its density; that is, the amount of mass per unit volume (g/mL).
My guess is that when someone talks about milligrams of a liquid, they’re either a)using a malapropism, b)talking about a liquid with the same density as an implied reference liquid (perhaps water?), or c)talking about the quantity of some ingredient in suspension or solution in a given quantity of liquid. The examples you have in mind probably fall in category c). For example, a fish oil capsule may be advertised as containing 300 mg. of EPA and DHA. This means that 300 mg. of EPA and DHA are in suspension or solution in the liquid inside the capsule. The total volume of liquid in the capsule is unadvertised because it’s considered irrelevant by the average consumer.
It depends on the density of the liquid in question. Density is measured as mass divided by volume. Therefore, you would find the density by dividing the mg by the ml. Because different substances have different densities (i.e. salt vs. fresh water), they also have different numbers of mg per ml. Catching what I’m throwing?