扩散与渗透
At the end of this lab, students should know...
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Q1: How do you prepare phenolphthalein solution for the diffusion indicator?
Weigh 1 gram of phenolphthalein and add it to a beaker containing 100 milliliters of 95% ethanol. Stir until the phenolphthalein fully dissolves into the ethanol. This solution serves as the diffusion indicator and will be added to the agar later to visualize pH changes during the experiment.
Q2: What is the correct procedure for preparing a 0.1 molar sodium hydroxide solution?
Measure 80 milliliters of water into a beaker and add 0.4 grams of NaOH. Stir until the solute dissolves completely, then bring the total volume to 100 milliliters with additional water. This creates a 0.1 molar basic solution used in the agar preparation.
Q3: How should you prepare the agar with phenolphthalein indicator?
Weigh 20 grams of dehydrated agar powder and add to 1 liter of water. Heat to near boiling until fully clear, then cool to 55°C. Add 10 milliliters of phenolphthalein ethanol solution and slowly add the 0.1 molar sodium hydroxide until the agar turns vibrant pink. Pour to 3 centimeters depth in a tray and refrigerate for several hours.
Q4: What steps are involved in preparing a 1% starch solution?
Weigh 10 grams of soluble starch and add to 500 milliliters of distilled water on a magnetic stir plate. Allow the starch to dissolve completely, then bring the final volume to 1 liter with additional distilled water. This solution is used as a test substance in dialysis tubing experiments.
Q5: How do you prepare 1 molar NaCl and dextrose solutions?
For 1M NaCl, dissolve 58.4 grams in 500 milliliters of distilled water in a 1-liter container, then bring volume to 1 liter. For 1M dextrose, add 180.2 grams of dextrose powder to 500 milliliters of distilled water in a 1-liter beaker, then bring to 1 liter. Both solutions are used to test osmotic effects through dialysis tubing.
Q6: How should dialysis tubing be prepared and stored?
Cut dialysis tubing into 20-centimeter pieces and soak them in distilled water, keeping them moist at all times. Excess tubing can be stored at 4°C in 20% ethanol to prevent bacterial growth. Proper preparation ensures the tubing remains flexible and functional for osmosis experiments.
Q7: What is the correct ratio and procedure for preparing hydrochloric acid solution?
Measure 25 milliliters of HCl and add to 475 milliliters of water to create approximately 500 milliliters of dilute acid solution. This diffusing acid is used to test how substances move across agar and demonstrates principles relevant to macromolecules identification using indicator solutions.