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Diffusion Probes and pH Lab


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Students use Vernier probes to measure the change in pH as various concentrations of acids and bases diffuse through dialysis tubing.

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Diffusion Probes and pH Lab

  1. 1. Open your lab notebook to your table of contents and fill in the information below Date Title Partners Pages 7 October Diffusion & pH (will be assigned)
  2. 2. Turn to the next blank page in your lab notebook and write the following: <ul><li>Title: Examining the rate of diffusion of unknown concentrations of acids and bases, into dH 2 O, using Vernier Probes. </li></ul>
  3. 3. Materials <ul><li>Each group will have: </li></ul><ul><li>1 probe </li></ul><ul><li>1 beaker of dH2O </li></ul><ul><li>1 sample to test </li></ul><ul><li>1 clip to hold the sample </li></ul>
  4. 4. Write the following in your notebook. <ul><li>Sample number: __________ </li></ul><ul><li>Color of sample: ___________ </li></ul><ul><li>Initial pH of dH 2 O: __________ </li></ul><ul><li>Final pH of dH 2 O: __________ </li></ul>Sample# Slope of the line (m) Molarity 1 2 3 4 5
  5. 5. IMPORTANT! <ul><li>These substances can burn your skin </li></ul><ul><li>Do not get the Vernier probe bases wet </li></ul><ul><li>Be gentle with pH probes </li></ul>
  6. 6. Setting up your probe <ul><li>Give the probe to one person in your group. </li></ul><ul><li>File, New </li></ul><ul><li>Click Mode </li></ul><ul><li>Click the white box next to “rate.” Type in 10 </li></ul><ul><li>Click the white box next to “length.” Type in 5 </li></ul><ul><li>Using the drop down menu and select “min.” </li></ul><ul><li>Click “OK.” </li></ul>
  7. 7. <ul><li>Plug in the pH probe into the top of the base where it says “CH 1.” </li></ul><ul><li>Place the base into the plastic bag </li></ul><ul><li>Unscrew the tube at the end of the pH probe </li></ul><ul><li>Place the probe into a beaker of dH 2 O </li></ul><ul><li>Watch the red box on the screen until the pH reaches between 7.3 and 7.5 </li></ul>
  8. 8. <ul><li>Set up your sample </li></ul><ul><li>Press the play button on the screen of the base. </li></ul>
  9. 9. At the end of 5 minutes <ul><li>Graph button </li></ul><ul><li>Analyze </li></ul><ul><li>Curve fit of pH </li></ul><ul><li>Choose fit, linear </li></ul><ul><li>Write down the “m” number </li></ul>
  10. 10. Sample# Slope of the line (m) Molarity 1 2M HCl 2 1M HCl 3 Water 4 1 M NaOH 5 2 M NaOH
  11. 11. What is Molarity? <ul><li>Molarity is a measure of grams of a substance per liter. </li></ul><ul><li>M = g/L </li></ul><ul><li>The higher the Molarity, the higher the concentration of a substance. </li></ul>
  12. 13. Analysis <ul><li>Draw the general shape of each graph </li></ul><ul><li>How does Molarity relate to rate of diffusion? </li></ul><ul><li>For each solution was the water hypotonic, hypertonic or isotonic to the sample in the bag? </li></ul>