Lessons · Nursing · percent solutions: g per 100 mL
A percent solution is grams in every 100 mL
A solution labelled a percent holds that many grams of solute in every 100 mL: 0.9 percent is 0.9 g per 100 mL, so the grams in a bag are the percent times the volume divided by 100.
Hone is a place to practise a career, one idea a day. This is one of its lessons, written out in full and free to read without an account.
What it is for
A pharmacist asks how many grams are in the bag you just hung, and the bag only says a percent. It is one multiplication, and it is the same arithmetic whether the bag is 100 mL or a litre.
How to think about it
Read the percent as grams per 100 mL. To get the grams in a bag, multiply the percent by the volume and divide by 100. To get the volume that holds a given number of grams, divide the grams by the percent and multiply by 100. Keep grams and millilitres on their own numbers.
Worked example
5 percent = 5 g per 100 mLThe definition, written as a rate.
Grams in 500 mL = 5 × 500 / 100 = 25 gPercent times volume over a hundred.
0.45 percent in 1000 mL = 0.45 × 1000 / 100 = 4.5 gA weaker solution in a bigger bag.
Volume of a 2 percent solution holding 6 g = 6 / 2 × 100 = 300 mLThe other direction: grams over percent, times a hundred.
Your turn
How many grams are in 250 mL of a 4 percent solution?
4 × 250 / 100 = g
Solve one, graded on the server
The trap
Reading a percent as grams per litre. Ten percent is 10 g in 100 mL, which is 100 g in a litre, not 10. The hundred in the formula is the whole point of the word percent.