Lab Report: pH Name: _________________________________________________________ Materials Needed You will need the following materials for this lab. • • • • • • • • • • • • • Red cabbage Coffee filter or paper towel Container for water (at least 250 ml or 1 / 2 pint) Three transparent cups (about 100 ml or 3 ounces) or other similar containers Hot water (e. g. , from a faucet, heated in a microwave oven, etc. ) Thermometer Vinegar Baking soda Safety goggles Tongs or fork Eyedropper or drinking straw Craft stick or toothpick Extra sticks or drinking straws for stirring
Hypothesis In this lab, you will compare the pH ranges of vinegar and a solution of water and baking soda. Do you think vinegar is an acid or a base? What about the baking soda? Write down your hypothesis now. Procedure Carry out the following steps to complete this lab. 1. Peel off several red cabbage leaves and tear them into pieces about 2. 5 cm (1 inch) square. Place the red cabbage pieces into the container. 2. Cover the cabbage pieces with hot water (not boiling water) and soak for about 30 minutes.
As a safety precaution, use the thermometer to make sure that the temperature of the water is not higher than 50 degrees Celsius (about 125 degrees Fahrenheit). © KC Distance Learning 3. With tongs or a fork, remove and discard as many cabbage pieces from the container as you can. 4. Carefully pour the remaining cabbage water from the larger container through the coffee filter into the three smaller cups or other transparent containers. 5. Note the purplish or dark blue color.
If the cabbage water has a pH of about 7. 0, which is typical for plain tap water, the color will be more purplish. If your water is treated by a water supply facility, it may have a pH around 8. 0, resulting in a dark blue color. This water color is your baseline. You will be comparing other colors to this as you proceed. 6. Use a drinking straw or eyedropper to transfer vinegar from its container to one cup of cabbage water, five drops at a time.
Stir the cabbage water after each vinegar transfer. Note any color change. Continue transferring vinegar five drops at a time until the color of the cabbage water has changed to a color different from that of the original cabbage water. 7. Use a craft stick or toothpick to transfer baking soda from its container to another cup of cabbage water, just a few grains at a time. Stir the cabbage water after each baking soda transfer. Note any color change.
Continue transferring baking soda a few grains at a time until the color of the cabbage water has changed to a color different from that of the original cabbage water. 8. The THIRD cup is your baseline cup. If you tap water is neutral, its color should be mostly purple, but it may be more bluish if your tap water has been treated by your county or city water supplier. 9. Record the color of the water after your final additions of vinegar or baking soda. What pH does each color represent? Is vinegar an acid or a base?
How about baking soda? Observations/Data Record the observations and/or data you collected here. © KC Distance Learning Lab Evaluation What strengths and weaknesses did you find in the experimental design? Is there anything you would do differently next time? How, if at all, would you do the experiment differently if you were to do it again? Discussion After you complete your lab, discuss your results in the course discussion board. Summarize the responses to your discussion here. © KC Distance Learning