Antacid Lab

The Great Antacid Culminating Lab

Purpose: To determine which antacid tablet is the most effective.
Materials: 3 different antacid tablets, thymol blue, droppers, pH probe and necessary cables, pH probe holder, retort stand, 1 mol/L HCl, droppers, five 150 mL beaker, mortar and pestle, graduated cylinder, balance, weighing dish, stir rod
Procedure:
1) Gather all the equipment you will need to do the lab. You will be working in groups of 3
2) Calibrate the pH probe as you practiced the day before. Make sure your pH probe is properly calibrated. If your pH probe is not calibrated properly, then all of your results will not be valid.
3) Obtain samples of the 3 antacid tablets you will be using. Crush the first antacid tablet using the mortar and pestle. Carefully measure 1 g of the powder using the balance and place this powder in a small beaker. To the powder, carefully add 50 mL of tap water.
4) Carefully add 4 drops of thymol blue to the beaker. Do not forget to add indicator since you will not see a color change if you do not add it!
5) Carefully insert the calibrated probe into the mixture. Take a pH reading. This is your first reading at 0 drops of HCl.
6) Carefully add 25 drops of HCl into the beaker while stirring with a stir rod and take a pH reading. After every 25 drops, take a pH reading. Make sure you are writing down your results, since you will need these to complete the lab write-up!
7) The goal is to get the pH of the solution as close to pH 2.0 as possible (hint: The solution will start to turn pink as the pH approaches 2.0)
8) After the pH reaches 2.0, make sure you have recorded all of the data. You should now have a table with two columns: number of drops of HCl and pH
9) Repeat steps 3-8 with the other two antacid tablets. Be sure to rinse all glassware before doing the other tablets.
Table of Rough observations
# of drops of antacid pH Antacid #1
Antacid #2
Antacid #3
0

25

50

75

100

125

150

175

200

225

Discussion: Answer the following questions
1. Why was it necessary to stir the mixture while you added HCl?
2. What did the color change of the solution indicate about the pH of the mixture?
3. Based on your results, which tablet is the most effective antacid and why?
4. If you had to buy an antacid, what things would you look for or consider?
5. What was the active ingredient in your antacid? Why aren’t bases like NaOH used as antacids?
6. Discuss 3 sources of error that your group encountered in this lab. Be sure to discuss what the source was and how it affected the results you obtained.

Tips for a Successful Lab Report
The Write-up: Refer to Lab Report Requirements for David Suzuki Secondary School posted on Angel and MyClass. Your report needs to have a title page, introduction, purpose, hypothesis, Materials, procedure, Observations, results and discussion.
A) Title page: The title page should be the 1st page of the report and should include an accurate title, the teacher’s name, your name, your partner’s names, the date, school name and the rubric.

B) Introduction: Two to three paragraphs in length. The introduction should provide enough background information so that someone with very little knowledge in chemistry can gain enough understanding to read and understand your lab. It should include a discussion on: what acids and bases are, what are pH indicators, stomach acid, antacid tablets and how they work, what the pH scale is and what are the pH of acids and bases.

C) Purpose: 2-3 sentences in length. It is a statement of why you did this lab

D) Hypothesis: 1-2 sentences in length. Based on what you know of acids and bases, which antacid tablet will be the most effective and why.

E) Materials: A detailed list of all the materials used to complete the experiment. Point form is fine

F) Procedure: A detailed, numbered step-by-step guide to how to do the lab

G) Observations: Your final observation should be summarized into a table such as:
Antacid
Mass of Antacid used Number of drops of HCl Needed
Initial pH
(Before HCl)
Final pH
(After HCl)
Observations

H) Results: Draw a graph with the # of drops of HCl on x-axis and pH on y-axis. You will draw graphs for all the antacids on the same set of axes. Use a legend to identify the lines. Calculate the slope of the lines. The slope calculation will allow to identify the most effective antacid.( Remember the most effective antacid is the one that can cause minimum pH change with maximum amount of HCl)

I) Discussion: Answer the 6 questions found at the end of the lab. Answer the questions in the same order as they are asked and be sure to number your responses 1 – 6.