Concentration required

Well, I learnt a lot about how maths is used in healthcare contexts from working on the new book. Here's an interesting something I didn't know before.

When you see the concentration of a chemical given as a percentage, such as the commonly-used sodium chloride 0.9%, what exactly does this 0.9% mean?

Well, when a solid (like sodium chloride) is dissolved in a liquid (water) then the concentration of the solution is given as weight by volume (w/v). So, the 0.9% is understood to mean 0.9 grams in 100 millilitres of solution.

Similarly a solution of dextrose 5% has 5 grams of dextrose dissolved in 100 millilitres of the solution.