Experiment 2.3: What Household Substances are Acidic or Basic? (Refer to Attachment for background information)
In the following experiment, you will be using pH test strips to determine the pH of various household substances. pH stands for “potential hydrogen” and is broken into a scale of 1 – 14 to indicate the acidity or basicity of a solution. Generally speaking, more hydrogen ions in a solution correlates to lower pH values, and more acidic solutions. Conversely, fewer hydrogen ions correlates to higher pH values, and more basic solutions. 7 is located in the middle of this number scale, and represents neutral solutions.
Note that many strong acids and bases do not have a pH that is indicated on this scale. For example, lead battery acid has a pH that is below one.
Refer to the color key provided in the module with your pH test strips to determine which color corresponds to each pH value. In this way, pH paper allows scientists to determine to what degree a substance is acidic or basic and can provide an approximate pH value.
5 mL 4.5% Acetic Acid (Vinegar), C2H4O2
(3) 100 mL Beakers
(3) 250 mL Beakers
10 mL Graduated Cylinder
(10) pH Test Strips
5 mL Sodium Bicarbonate (Baking Soda)Solution, NaHC)3
*4 Liquid, Household Solutions
*Water Source (Jug or Sink)
*You Must Provide
Procedure (See Pictures on page 3 and 4 forInitial and Final results in order to answer post-lab questions)
1. Find four household substances to test (ex: grape juice, lemon juice, dishwashing liquid, milk, tomato juice, shampoo, corn starch solution, etc.). You will use the vinegar (acidic) and sodium bicarbonate (basic) solution provided in your kit as standards.
2. Predict the pH of each substance before testing with a pH strip. Record your predictions in Table 4 for each substance.
3. Use the permanent marker to label each of the beakers with the name of one of the six solutions. It does not matter which size beaker is used for the different solutions.
4. Use the graduated cylinder to measure and pour five mL of vinegar into the beaker labeled “Vinegar”.
5. Repeat Step 4 with each of the five remaining solutions and beakers.
6. Measure the pH of each solution by dipping the pad of the pH strip into the solution for 5 – 10 seconds and comparing it with the pH test strip key (located in the lab module). Record your results in Table 4 for each substance.
Table 4: pH Values of Common Household Substances
Substance pH Test Strip Color pH Value
1- Acetic Acid (Vinegar) Orange 5
2- Sodium Bicarbonate Solution (Baking Soda) Dark Green 8
3 – Lemon Juice Orange 5
4 – Milk Light Green 6
5 – Tomato Juice Orange 5
6 – Grape Juice Orange 5
1. What is the purpose of determining the pH of the acetic acid and the sodium bicarbonate solution before testing the other household substances?
2. Name two acids and two bases commonly found in a grocery store.
3. What similarities do you observe about the acids you identified other than their pH measurements? What similarities do you observe about the bases you identified other than their pH measurements? What can you conclude generally about acids and bases that a person uses regularly based on these similarities?