pH Determination Lab INTRODUCTION In our daily life, we frequently encounter acids and bases. Many foods, such as citrus fruits and tomatoes contain acids. Many household cleaners, such as ammonia, contain bases. pH is a measure of the acidity or basicity of an aqueous solution. pH can be measured in a variety of ways. Two common ways of measuring pH are using pH paper and a digital pH meter. In this lab we will be using pH paper to measure pH. pH is related to the hydronium ion concentration using the following equation:
pH = -log[H3O+] The range of pH is 0-14.
pH < 7 is acidic pH > 7 is basic pH = 7 is neutral
Prepare your notebook. When the lab is complete your lab notebook should include the following:
1. Include pH Determination Lab in the Table of Contents 2. Write the title of the lab on the top of the page. 3. Date/number the page (if you work on it over a few days, date each time you are
working). Sign in your lab notebook each time you stop working. 4. Record the Purpose of Experiment in your own words. Remember the purpose is the
overall question that will be answered by collecting the data and doing any requested calculations.
5. Indicate PPE (personal protection equipment) required while performing the lab: goggles, gloves, lab apron, and closed-toed shoes.
6. Prepare your notebook to record observations by writing tables. 7. Complete the post-lab question.
pH Determination Activity: In this lab you will measure the pH of several products found in your household using pH paper. Keep in mind the pH scale and how it is related to the acidity and basicity of a product. Also consider the limitations of using pH paper instead of a digital pH meter. Materials/Equipment needed: pH paper; allow the paper to be exposed to air until it is a yellow color (pH = 7 below) gloves pipettes 1 Tbsp each of 3 food items and 3 cleaning items. They should be water soluble and not highly colored. Weighing boats
Procedure: Part 1: Colorimetric determination of pH
1. To complete part 1, you will need a weighing boat, pipette and a strip of pH paper. Do not place the dropper directly into the containers of the food items or the cleaning items.
2. To determine the pH of each solution using broad range indicator paper, place a single drop of the chemical on the paper and compare the color of the paper with the color chart below. The reading should be done within 2 minutes of applying the drop because some chemicals will destroy the dyes that create the different colors. DO NOT DIP THE STRIP INTO THE SAMPLE.
3. Record the item tested and the pH in the data table.
Item used pH
1. What general observation can you make about the pH of food items?
2. What general observations can you make about the pH of cleaning supplies?
3. What problems are associated with colorimetric methods for pH determination?
4. Pick three solutions above and calculate the free hydronium ion concentration, [H3O+] using [H3O+] = 10-pH.
Works cited: Mullins, N.J., & Milczanowski, S.E. (2020). Lab Manual for Introductory Chemistry CHM1025C/CHM 1032C. Jacksonville: FSCJ Copy Center
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