Lab 2: Investigating pH of Various Household Products Lab
In an aqueous solution (any solute in a water solvent), a very small percentage of water molecules break apart into ions. The ions formed are H+ (hydrogen ions) and OH- (hydoxide ions). A correct balance of hydrogen ions and hydroxide ions is necessary for chemical processes to work correctly within a cell. A solution would be called neutral when the amount of H+ and OH- is the same. A solution is considered acidic when the number of hydrogen ions is greater than the number of hydroxide ions. Conversely, a solution is considered basic when the number of hydrogen ions is less than the number of hydroxide ions. An acid is a molecule that donates H+ to a solution, making it acidic. Hydrochloric acid (HCL) is an example of an acid. It disassociated into a hydrogen ion and a chloride ion. A base is a molecule that adds hydroxide ions to a solution, making it basic. Sodium Hydroxide (NaOH) is an example of a base. It dissociates into a sodium ion and a hydroxide ion.
The pH of substances can be found using a variety of tools and indicators within a laboratory setting. One of the simplest tools, litmus paper, actually exists in three forms; red, blue, and wide-range. Acids will turn blue litmus paper red and bases will turn red litmus paper blue. Wide-range pH paper, in comparison, determines the exact numerical pH reading of each substance. In this lab you will test various household products of your choosing to see whether they are primarily acidic or basic. You will then use wide range litmus paper to get their exact reading. Finally, you will use wide-range litmus paper to observe what happens to a solution of NaOH when you add drops of HCl to it.
Pre-lab Procedure (Must be completed for day of lab)
1. On the next full page in your lab notebook, write the number, titleand date of this lab.
2. Write the purpose of the lab.
3. Write the procedure for section A and B into your lab notebook.
4. Answer the following “PreLab” Questions.
A. Define “acid” and base” using the terms hydrogen ion and hydroxide ion.
in terms of –OH and H+, What is an acid? A base?
B HCl is said to be an acid, that donates H+ to a solution. How do you think this might happen? (Hint- what two elements are in HCl?)
C. NaOH is said to be a base that can remove H+ from a solution. How do you think this might happen? (Hint- as above)
5. Create a data section in you laboratory notebook in which you can collect your data for procedure A. You may rewrite this into your notebook using a straight edge or cut an paste this chart out. The data will include your guess (acidic, basic, or neutral), litmus paper results (acid, neutral, or basic) and the actual numerical pH reading.
Substance / Guess / Litmus / pH1.
2.
3.
4.
5.
6. Create an observation page.
Procedure
A. Litmus Paper Tests
1. Within the data chart, indicate the 5 substances you and your partner would like to test the pH of based on the selection Ms. Franczyk brings into class.
2. Label 5 beakers, one for each substance being tested. Pour about 5ml of each into the correct beakers. You can estimate the 5ml using the key on the side of the beaker (don’t waste time measuring).
3. Collect 5 strips of blue litmus paper, 5 strips of red litmus paper and 5 strips of wide-range pH paper.
4. Back at your lab bench, make an educated guess as to whether each substance is acidic, basic, or neutral. Mark your guesses in the data chart.
5. Dip a blue litmus paper into substance 1. Dip a red litmus paper into substance 1. Mark your results (acid or base?) in the data chart. Remember- acids turn blue litmus paperred and bases turn red litmus paper blue. You need to use BOTH papers to figure out if a substance is acid or base.
6. Dip wide-range paper into substance 1. Use the meter on the side of the dispenser to check your results. Mark your results in the data chart.
7. Repeat steps 5 and 6 for substance 2-5.
B. Is it Magic?
8. Add 100 mL to a beaker. Drop in 3 drops of phenolphthalein.
9. One by one, add some drops of ammonia. Continue to add until you witness a change in the appearance of the water.
-Observation #1 What happened when you added the ammonia to the phenolphthalein and water solution?
10. Now, to the same solution, add one by one some drops of vinegar.
-Observation #2 What happened when you added the vinegar to the phenolphthalein, water and ammonia solution?
Analysis and Conclusion Questions (To be answered in complete sentences in your lab notebook).
1. What is the possible range of pHs? Which side (lower or higher) is acidic?
2. Which of the five substances you tested were acidic? How did you know using the Litmus paper?
3. Which of five substances you tested were basic? How did you know using the Litmus paper?
4. Were any substances neutral? How do you know?
5. Did the results using litmus pH paper agree with the results using the wide-range paper?
What additional information did the wide-range pH paper provide?
6. Phenolphthalein is a pH indicator that turns red when pH rises above 8.3. Knowing this, explain what happened in throughout Experiment B.