Name: ______Date: ______Block: ______

Testing pH of Household Substances

Admit Slip Directions: Read the background information and answer the pre-lab questions that follow.

Liquids all around us have either acidic or basic (alkaline) properties. For example, acids taste sour; while bases taste bitter and feel slippery.Just like weight is measured in pounds and length is measured in meters, we use pH to measure how acidic or basic a solution is. A pH of 7 represents a neutral solution that is neither acidic nor basic, such as water. The pH scale ranges from 0 (very acidic) to 14 (very basic). The strength of the pH scale is determined by the concentration of hydrogen ions (written as H+, which is a hydrogen with an electron removed), where a high concentration of H+ ions indicate a low pH (acid) and a low concentration of H+ ions indicate a high pH (base).

The scale is logarithmic. This means that each difference of one pH unit means a 10-fold difference in acidity. For example, a solution with a pH of 8 is 10 times more acidic that a solution with a pH of 9. In other words, a pH of 8 is 10 times less basic than a pH of 9. Strongly acidic and basic solution can be quite harmful to the external environment of living systems. Strong acids and basis can burn skin badly, and even minor imbalances in internal pH can disrupt the normal regulation of cells. Each part of your body has an optimal pH that it must maintain to work correctly, just as you saw with enzymes. Thankfully, your body has solutions called buffers that help resist changes in pH. This is the reason you can drink acidic soda, and your blood pH stays relatively neutral. Without these chemical buffers, you would die simply from eating! Buffers do have their limits though, and can only help maintain levels within a certain range. So I wouldn’t recommend cutting open your stomach or jumping into acid!

In this lab, you will use aliquid pH indicator to test common household liquids and determine their pH levels. When you mix the indicator with different household liquids, you see a color change. Through this color change, you will be able to successfully identify the approximate pH of common household liquids using the provided indicator scale.

Pre-Lab Questions:

  1. What pH represents a neutral solution, meaning it is neither acidic nor basic? pH of ______
  2. If you go below that number you get more ______, and if you go above that number you get more ______.
  3. The scale is ______, meaning as you increase by one unit of pH, the difference is ______times the original unit.
  4. This means that a pH of 9 is ______times more basic than a pH of 7, meaning it is a

( stronger / weaker ) base.

  1. Just as a pH of 3 is ______times more acidic than a pH of 6, meaning it is a

( stronger / weaker ) acid.

  1. A solution with a pH of 4 is a(n) ______.
  2. A solution with a pH of 7 is ______.
  3. A solution with a pH of 10 is a(n) ______.
  4. What is another word for basic? ______
  5. The strength of the pH scale is determined by the number of ______ions, with a high concentration resulting in an______.

Group Roles:

Group Manager
(protocol/materials/
cleanup) / Materials Collector
(solution dropper) / Indicator Expert (indictor dropper) / Data Recorder / Materials Returner
(solution disposal)
Group Member: / Everyone

Prediction Chart

Directions: Write the names of at least seven solutions of your choice from around the room, then make a prediction about each solution’s pH from 1 to 14 and write if it would be an acid or a base.
You will fill out the “Measured pH” columnsafter you conduct the experiment.

Solution / Predicted: pH / Predicted:
Acid or Base / Measured: pH / Measured:
Acid or Base
1. tap water
2.
3.
4.
5.
6.
7.
8.
9.
10.

Experimental Protocol

  1. Put on your lab goggles- you do NOT want any of these materials getting in your eyes. (Role: Everyone)
  2. For each solution, pour a small amount into one of the plastic cups, and bring back to your table.
    (Role: Materials Collector)
  3. Use a pipette (one for each solution) to place a few drops in a “well” (small circular dish).
    (Role: Group Manager)
  4. Use a separate pipette to grab a few drops of indicator, and drop into well until the color changes.
    (Role: Indicator Expert)
  5. Match color to pH scale provided and record your results in the sheet. (Role: Everyone)
  6. Return used cup to original station along with pipette. (Role: Materials Returner)
  7. Gather next solution and repeat in the same fashion. (Role: Materials Collector)
  8. After completing at least 5 solutions, go find a strong acid and strong base and bring back to table.
    Using separate pipettes, drop equal amounts of each solution into a single well (a few drops each).
    (Role: Materials Collector)
  9. Use indicator to test for pH. (Role: Indicator Expert) What is the resulting pH? Record below.

Solution 1 & pH / Solution 2 & pH / Combination pH?
  1. What occurred when the acid and base interacted? ______
  2. Return all materials to stations, empty well down the sink, wash thoroughly, and return to seats.

Analysis Questions: (Use complete sentences!!!)

  1. Which pH measurements differed from your predictions? For which solutions were your predictions correct? ______
    ______
  2. Learning that your blood has a pH of about 7, and your stomach has a pH of about 2, which of the solutions you tested could be harmful to the pH balance of your organ systems? Why? ______
    ______
  3. Why is proper pH balance important? ______
    ______
  4. We don’t usually check and test the pH of the food and drinks we consume. So, how is it that they do not cause harm to the body? (Hint: Read the second paragraph of the introduction!) ______
    ______
  5. What would happen if your stomach ruptured and some of your gastric juices ended up flowing freely inside your body? ______
    ______
  6. Using the final part of your experiment (Parts 8 & 9: mixing acid and base), try to explain why acid rain could be detrimental to the environment. ______
    ______
  7. What is your one main “takeaway” from this lab? What did you learn? (Note: Saying “nothing” or a similar answer will result in a zero.)______
    ______