What effect does diluting a pure substance have on the pH? Explain your reasoning as to why this effect is seen?

CHM 1020L

Introduction to pH lab

This lab uses the pH Scale Basics simulation from PhET Interactive Simulations at University of Colorado Boulder, under the CC-BY 4.0 license.

https://phet.colorado.edu/sims/html/ph-scale-basics/latest/ph-scale-basics_en.html

Learning objectives

  1. Understand the pH scale
  2. Relate the value of pH of a substance to whether a given solution is acidic or basic.
  3. Predict the effect of volume on pH of pure substances
  4. Predict the effect of dilution on pH of pure substances
  5. Organize a given list of substances from most acidic to most basic with supporting evidence.
  6. Apply knowledge gained in the experiment to explain relevant real world situations.

Pre-lab

Cite your sources for each answer at the very end of the document – a video/ a website etc.

  1. What is the pH of distilled water generally and why is it that particular pH?
  • What is the pH range for an acidic solution? Which is higher in concentration: H+ ions or OH ions?
  • What is the pH range for a basic solution? Which is higher in concentration: H+ ions or OH ions?
  • What is the pH of blood? What happens if the pH of blood changes?  
  • What conditions can cause a change in the pH of blood? List 2 conditions that cause the pH of blood to increase and 2 conditions that cause the pH of blood to decrease. Explain briefly why these conditions cause the pH of blood to increase or decrease and what we can do to avoid them.
  • In the experiment what precautions must be taken to ensure that your pH probe gives you the correct reading?

Observations

Table 1

pH of pure solution and nature of the solution (acidic/basic/neutral)

Identity of liquid (pure solution)pH of 0.30 L of pure solution and nature of solutionpH of 0.50 L of pure solution and nature of solutionpH of 1.00 L of pure solution and nature of the solution
Drain cleaner13.00basic  13.00basic
         
         
         
         
         
         
         
         
         
         
         

Table 2

pH of pure solution and diluted solution and the nature of the solution (acidic/basic/neutral)

Identity of liquid (pure solution)pH of 0.50 L of pure solution (get values from Table 1) and nature of solutionpH of 1.00 L of pure solution (get values from Table 1) and nature of solutionpH of diluted mixture (0.50L of pure solution + 0.50 L water) and nature of solution
Drain cleaner  13.00basic  12.70basic
         
         
         
         
         
         
         
         
         
         
         

Post lab questions

  1. What effect does an increase in the volume of a pure substance have on the pH (for example does the pH of 0.30 L of the substance vary from the pH of 0.50 L of the substance) Explain your reasoning as to why this effect is seen?
  • What effect does diluting a pure substance have on the pH? Explain your reasoning as to why this effect is seen?
  • How will adding water affect the pH of the following solutions. Support your conclusions with data from your experiments.
  • An acidic solution
  •  A basic solution
  • A neutral solution
  • Draw 3 general conclusions about the kinds of acidic and basic substances present on the list (for example. can you group certain kinds of substances together?) 
  • In general when someone is experiencing symptoms of heartburn, they suggest that the person drink lots of water. Does that help? Explain your answer using the concepts you learned in this lab.
  • What conclusions can you draw about the kinds of foods featured in this simulation? Is that generally the case with most of the food we eat? Support your conclusions and cite your sources.
  • Consider some common drinks – Gatorade, orange juice, green tea, vinegar, baking soda.
  • Organize these foods from most basic to most acidic. Explain your reasoning (and cite your sources)
  • Among all these foods which will have the highest pH if you dilute with an equal amount of water? Explain.
  • Among all these foods which will have the lowest pH if you dilute with an equal amount of water? Explain.

Sources used: Cite your sources below

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