Solutions & Dilutions Practice You can do it!

Percent Weight by Volume solutions The number of grams of a solute in 100mL of solution is indicated by the percent concentration Ex: a 20% solution has twenty grams of solid dissolved in distilled water to together equal 100mL of solution If you want to make a different volume of solution, determine the new proportion of solute by cross multiplying Ex: 20 g = X g 100 mL 50 mL

1. How would you prepare 100 mL of a 30% (w/v) solution of polyethylene glycol (PEG)? ______g PEG + water to = ________mL

2. How much solute is needed to make 25 ml of a 9% (w/v) solution of NaCl? ______g NaCl + water to equal 100 mL ____g = _____g 100 mL _____mL How much water do you add to the solute volume to make the final solution?

3. How would you make 200 ml of a 15% (w/v) solution of glucose? ______g glucose + water to equal 100 mL ____g = _____g 100 mL _____mL How much water do you add to the solute volume to make the final solution?

4. Saline drops are a 0. 9% solution 4. Saline drops are a 0.9% solution. How many grams of salt are in a 60mL travel size bottle? ______g salt + water to equal ____mL ____g = _____g ____ mL _____mL

Diluting (making less concentrated) a solution A stock solution of known concentration (%) can be diluted using C1V1 = C2 V2 (concentration, volume) Use the concentration of the stock solution you have (C1), the concentration of the final solution that you want to make (C2), and the volume of this solution you need (V2). Solve to find the volume of the stock solution to use (V1). Watch the units! (80%) (V1) = (20%)(50mL) -> divide both sides to isolate the variable

5. How much of a stock solution of 95% ethanol is needed to make 200 ml of 70% (v/v) solution of ethanol? _____% (V1) = ____% (_____mL) How much DI water do you add to finish the solution?

6. You have 200 ml of 50X TAE. What volume of the 50X TAE is needed to prepare 25 ml of 10X TAE? _____ (V1) = ____ (_____mL) How much DI water do you add to finish the solution?

7. You have 10mL of a stock sol’n of ampicillin 7. You have 10mL of a stock sol’n of ampicillin. To use with children weighing under 50kg, it’s diluted to yield 30 mL of a 5% solution. C1 (____) = ____% (_____mL) What is the percent concentration of the stock ampicillin?