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.
In beta. This lesson was written for Hone and has not yet been checked by a licensed nurse. Practice material, not professional advice. What that means.
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.