Name ______
Acid - Base Indicators Lab
Ms. Garner
Background- A pH indicator is a chemical compound that is added in small amounts to a solution that the pH of the solution can be determined visually. The most basic indicator, Litmus Paper, just indicates whether a solution is an acid or a base. If the paper turns red (or pinkish) it is an acid. If the litmus paper turns blue, it is a base. A pH indicator is a chemical detector for hydronium ions (H3O+). Normally, the indicator causes the color of the solution to change depending on the pH. Indicators change colors at differing pH’s. You can determine the pH of a substance by using a series of indicators and comparing the results to the pH values on the indicator charts. For example, the indicator phenolphthalein remains colorless in a solution that has a pH lower than 8.8. If the pH of the solution exceeds 8.8, the solution containing phenolphthalein turns pink.
Safety- Acids and bases are corrosive and dangerous to the eyes. They can be skin irritants.
GOGGLES and APRONS must be worn at all times. Wash hands when finished with the
lab and clean lab space with soap and water.
Objective- To determine the pH of household acids and bases by using the color chart associated with
several indicators. See attached indicator chart.
Hypothesis:
In the chart below, record the use for the following household substances. Based on what you have learned about acids and bases and what you know about these household products, predict whether the substances will be acids, bases or neutral.
ammonia / vinegar / Milk of magnesia / Sea water / water / aspirin / Gastric acid / lye / soda / Oven degreaser / Drano / Battery acidUse of substance
Acid,
base or neutral?
Pre lab questions:
1. What does the pH scale measure?______
2. What is the range of the pH scale?______
3. What is the pH of an acid? ______base? ______neutral?______
4. Would babies eat food that is acidic, basic or neutral? WHY?______
5. Why do lifeguards and pool maintenance people have to test the pH of swimming pools? ______
6. What harm would a low pH of a swimming pool do to people? ______
7. Acid Rain has a pH of around 5.8. Is this a strong acid or weak acid? ______Would this type of rain hurt you if it touched you? ______Why do you think acid rain is so harmful to the environment? ______
8. When people get acid reflux, they take Tums or Rolaids. What is the scientific purpose of Tums? ______
9. What properties of DRANO make it good for cleaning out household pipes? ______
10. What observation about a base would lead you to believe it is a base before you even test its pH?
______
USE your indicator chart to answer the following questions:
11. Which indicator changes pH between 3-4? ______
12. Which indicator changes pH between 0-2? ______
13. Which indicator changes pH between 8-9? ______
14. Which indicator changes pH between 7-8? ______
15. Which indicator changes pH between 5-6? ______
Experiment
Materials- 3-Spot plates Indicator chart
Indicators: Household acids and bases:
Blue Litmus paper 1. ammonia
Red Litmus paper 2. vinegar
Phenolphthalein 3. milk of magnesia
Bromothymol Blue 4. sea water
Methyl Orange 5. water
Methyl Red 6. aspirin
Methyl Violet 7. gastric acid
Phenol Red 8. lye
9. soda
10. oven degreaser
11. drano
12. battery acid
Part One Procedure-
1. Wear safety goggles at all times. (Acids and Base can be harmful if not handled properly).
2. DO NOT LET THE TIPS OF THE DROPPER BOTTLES TOUCH ANYTHING!!!!!
3. Clean and dry all spot plates.
4. Obtain the 12 household acids and bases, and red and blue litmus paper from your teacher.
5. Place a white sheet of paper under three spot plates. Label the paper according to the LITMUS chart below.
1 2 3 4 5 6 7 8 9 10 11 12
6. Place 3 -4 drops of each solution (1-12) in a well on the spot plate.
7. First, determine if each solution is an acid, base or neutral by Dipping the paper indicator into the solution and record your observation on the data table.
8. Clean and dry your spot plates for part two.
Part Two Procedure-
1. Wear safety goggles at all times. (Acids and Base can be harmful if not handled properly).
2. DO NOT LET THE TIPS OF THE DROPPER BOTTLES TOUCH ANYTHING!!!!!
3. Use the same labeled white sheet of paper. Label each indicator on the left of the paper as below.
1 2 3 4 5 6 7 8 9 10 11 12
4. Place 3 - 4 drops of each solution in a well on the spot plate according to the labeled paper.
5. React each solution 1-12 with 1 drop of phenolphthalein. Record color on chart.
6. Repeat steps 4 -5 with the rest of the indicators. Record results. (You will need to clean your well plates when you run out of wells.
Analysis:
Litmus test results:
Record the color that the red and blue litmus paper turn in the appropriate box. Then determine if the household substance is an acid or base.
ammonia / vinegar / Milk of magnesia / Sea water / water / aspirin / Gastric acid / lye / soda / Oven degreaser / Drano / Battery acidRED
Litmus
BLUE
Litmus
Acid or Base?
Indicator test results:
Record the color that the solution turns when you place ONE drop of the indicator in the well. When you have completed the series of indicators on each household item, then determine the pH household substance using your results and the indicator chart.
ammonia / vinegar / Milk of magnesia / Sea water / water / aspirin / Gastric acid / lye / soda / Oven degreaser / Drano / Battery acid1.
Phenolphthalein
2. Bromothymol blue
3. Methyl Orange
4. Methyl Red
5. Methyl violet
6. Phenol Red
What is the pH?
Conclusion: (WRITE ON A SEPARATE SHEET OF PAPER)
Summarize in paragraph form what you have learned about:
1) pH indicators
2) chemical and physical properties of acids and bases
3) chemical uses of household acids and bases.
Be sure to use scientific vocabulary in your conclusion, state whether or not your hypotheses were correct and how you knew and be sure to reference your data from the experiment.