Lab 1 Practice Problems
At the beginning of your next lab, please turn in the answers to the following three problems. Show all calculations (including units) on a sheet of paper (not your lab notebook). To receive full credit, make sure to answer all parts of each question.
1. a) How many grams of sucrose (MW=342) would you need to make 100mL of a 10-2 M sucrose solution? b) How many milligrams of sucrose would you need to make this same solution? c) Express 10-2 M as a millimolar (mM) concentration.
2. Compound Z has a MW of 100. Your lab partner weighed 25 grams of compound Z and dissolved it in water to a final volume of 1 liter. a) What is the concentration of the solution expressed as a percentage by weight (w/v)? b) What is the concentration of the solution expressed as molarity?
3. You need to prepare 2 methanol solutions for lab today: a) 300mL of 50% (v/v) methanol and b) 200mL of 25% (v/v) methanol. You have been supplied with 100% methanol and deionized water as well as graduated cylinders and beakers of the appropriate sizes, a magnetic stirrer and Teflon stir bars. How would you use these materials to prepare the two methanol solutions? Note that this question requires more than just showing the math involved. You need to write the steps involved in preparing the solutions, including when and how you use the provided materials.
4. The molecular weight of glucose is 180g/mol. To prepare a stock solution of glucose, you dissolve 1.8g of glucose in water to a final volume of 1.0L. This stock solution is then diluted as follows: 50mL of the stock solution is added to 450mL of water, and then 1.0mL of the diluted solution is added to 99mL of water. What is the µM concentration of the final solution?
5. You have been given a stock glucose solution with a concentration of 100mg/mL. To perform the glucose assay in lab today, you must dilute the 100mg/mL stock solution of glucose to concentrations of 80mg/mL, 60mg/mL, 40mg/mL, and 20mg/mL. You need to prepare 1mL of each dilution. Explain how you would make the 4 dilutions from the glucose stock solution.
6. For each of the following situations, please describe what you would do.
a. You just broke a beaker and broken glass is now on the floor.
b. You just spilled Tetrahymena on your arm.
c. You just finished pipetting some water and you now need to dispose of the pipette tip. Where do you put it?