Been out of school too long and need some help. I want to make a 15% potassium chloride solution from a 100% potassium chloride powder. How much powder should I mix into a set volume of water (e.g. 1 liter)

it depends on exactly which kind of percent you're using.

 

the most common percentage used in solutions is weight/volume, which means you'd put 15g in every 100 mL of solution (in other words, dissolve 15g in the minimum quantity possible and then top up to 100mL after it's dissolved)

 

other types are volume/volume (usually for liquids dissolved in liquids), weight/weight (often used in temperature-sensitive situations... volume changes with temperature, whereas weight doesnt) and mole percent (percentage based on the numbers of molecules of solute and solvent).

 

I'd guess you're almost certainly gonna want weight/volume, which means you'd need 150g for every liter of solution (not every liter of water, though... the volume of water will be different to the volume of solution. Just dissolve it then top up to 1L.)

Thanks,

 

I should have remembered that, but I appreciate the advice and will make it up as you suggest. Forgot that a ml of water is = to a gram of water. Oh - how the mind goes!!!