Water, pH, and Buffers

Water, pH, and Buffers

This document is not meant to be a substitute for a formal laboratory report. The Lab Report Assistant is simply a summary of the experiment’s questions, diagrams if needed, and data tables that should be addressed in a formal lab report. The intent is to facilitate students’ writing of lab reports by providing this information in an editable file which can be sent to an instructor.

 

Exercise 1:  Water and its Unique Properties

 

Data Table 1. Needle Observations.

Vertical ObservationsHorizontal Observations
  

 

Data Table 2. Paper Clips Needed to Break Surface Tension.

 

PredictionResult
_____ Paper clips_____ Paper clips

Data Table 3. Drops of Water.

PredictionResult
_____ Drops of water____ Drops of water

Data Table 4. Part 4 Observations.

Observations 

Questions

  1. How did the experiment in Part 1 demonstrate surface tension? Use your experiment observations when answering this question.

  2. In Part 1, when adding the needle to the water, which approach worked best to balance the needle on the water—the vertical or horizontal placement? Explain your answer.

  3. In Part 2, how did your paper clip estimation compare to your paper clip results?

  4. In Part 3, how were the properties of adhesion and cohesion demonstrated in the experiment?

  5. How did the activity in Part 4 demonstrate capillary action? Explain your answer using your experiment results and observations.

 

Exercise 3:  Testing Common Household Materials for pH Values

 

Data Table 5. pH Observations.

Well PlateItem TestedCommercial pH stripHomemade pH strip
ColorpHColorpH
1HCl  (hydrochloric acid)    
2NaOH (sodium hydroxide)    
3Distilled water    
4     
5     
6     
7     
8     
9     
10     
11     
12     

Data Table 6. Analysis of Results.

Well PlateItem TestedAcid/Base/
Neutral?
Explanation:
1HCl (hydrochloric acid)  
2NaOH (sodium hydroxide)  
3Distilled water  
4   
5   
6   
7   
8   
9   
10   
11   
12   

 

 

 

Questions

  1. Compare and contrast the results between the commercial and homemade pH test strips. Which test strips were more accurate? Explain your answer.

  2. Why is the pH scale important in science? Give several examples of scientific applications.

  3. What information about a chemical can be inferred from knowing its pH value?

  4. If a chemical has a pH of 3, how could you change its pH value to be more basic?

 

 

Exercise 4:  Buffers in a Living System

Data Table 7. pH Change of Buffered and Un-buffered Solutions.

 

 Un-buffered SolutionBuffered Solution
Initial pH  
+ 3 drops HCl  
+ 6 drops HCl  
+ 9 drops HCl  
+ 12 drops HCl  
+15 drops HCl  
+18 drops HCl  

 

Data Table 8. Graph of pH Changes.

Graph of pH changes
 

 

Questions

  1. Analyze the results of your experiment. Did the buffer resist changes in the pH? Explain your answer using your experiment results.

  2. Research the bicarbonate buffering system found in the blood stream. Write a paragraph or two discussing this system and how your breathing rate can cause acidosis and alkalosis.