You have the containers in front of you. How much should you measure out to make 200 mL of a 2% aqueous solution of sucrose?
fast and easy way: add 100 mL water to 100 mL of 4% sucrose
another way: add 4 grams of sucrose and make up to 400 mL
(note 2% is 2 grams in 100 mL; thus 4 in 200 mL)
You have the containers in front of you. You have added 1.8 grams of NaCl crystals to water and made it up to 200 mL. What percent solution have you made?
If 1.8 in 200 mL; how much in 100 mL? 0.9 grams.
Thus 0.9%
You have have the containers in front of you. You have taken 100 mL of the 5% lactose solution and added it to 400 mL of water to obtain 500 mL of what percent concentration?
CV=CV
5% x 100 mL = C x 500 mL
C = (5% x 100 mL)/500 mL; C = 1%
(Really tricky!) You add 10 grams of gasoline to 50 mL of water and then make it up to 100 mL by adding more water. What is the concentration of gasoline in the water?
oil and water don't mix! Neither does gasoline and water!
Your aquarium is over-grown with algae, and is too green for your meter to measure (can only measure up to 10 units of intensity). You add 10 mL of the green aquarium water to 10 mL of tap water and get a measurement of 9 units. How green in units was the original aquarium water?
CV=CV
9 units x 20 mL = X units x 10 mL
X units = (9 units x 20 mL)/10 mL = 18 units
Your supervisor tells you to replenish the exhausted supply of 1 M NaCl. The amount you had just used was only 50 mL, but the container will hold much, much more than that. You know you should responsibly make up a lot, and the amount is up to you. Two questions: how much NaCl do you use? How much water do you use?
You want to make up "a lot" - so why not make up a liter (1,000 mL).
1 M NaCl = 58 grams made up to a liter.
The prescription says that you should give one pill per every 20 kg of adult body weight. Your patient weighs 80 kg into which your pills must dissolve to form an effective concentration. How many pills do you have the patient swallow?
How many 20's in 80? 4. Thus 4 pills.