Lab

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• Teacher Guide.doc

Submitted by
Genia Harris      
Angleton High School
Angleton, Texas

Thanks to
Dow Chemistry Teacher Summit

Summary

In this lab, students will use their knowledge of acids and bases to determine the acidity and basicity of every day items by measuring pH using several different methods for determination.  Indications of pH may be determined using red & blue litmus paper, pH strips, and pH probes or pH meters. 

Grade Level

Middle and High School

Objectives

By the end of this lab, students should be able to

·         Idenitify which common daily use and household items are acidic or basic.

·         Determine what methods of determining pH are situationally more accurate.

·         Properly use various lab methods of testing pH including using red & blue litmus paper, pH strips, and pH probes or pH meters. 

Chemistry Topics

This lab supports students’ understanding of

·         Acids and Bases

·         pH

·         Indicators

Time

Teacher Preparation: 30-45 minutes

Lesson: Two 50 minutes periods

Materials (per group)

• Red litmus paper
• Blue litmus paper
• Universal pH paper  
• ·   pH meter & probe
• ·   Paper towels
• ·   Ten 100 mL beakers
• ·   Labelling pen or marker
• ·   One 250 ml beaker
• ·   Wash bottle with distilled water
• ·   50 mL solutions of the following:
• o       Distilled water
• o       Lemon juice
• o       Tomato juice
• o       Maalox
• o       Ammonia
• o       Coke
• o       Corn Oil
• o       Shampoo
• o       Vinegar
• o       Dishwashing Liquid

Safety

• Always wear safety goggles when handling chemicals in the lab.
• Students should wash their hands thoroughly before leaving the lab.
• When students complete the lab, instruct them how to clean up their materials and dispose of any chemicals.
• When working with acids, if any solution gets on students’ skin, they should immediately alert you and thoroughly flush their skin with water.

Teacher Notes

·         Materials can be substituted and suggested amounts may be reduced.

·         Some additional pH background information can be found at this website.  

·         Make sure pH meters are working properly and are calibrated before students use them.  Teacher may have to also have to calibrate (depending on the quality of the probe) between uses if lab is done during different lab periods.

·         Go over, in detail how students are to use the pH meter and probe.

·         Be sure students have access or a copy of a pH scale.

·         Classroom management tips: This lab may be best utilized if students are in groups of 4.

·         This lab can be separated into stations and students can rotate to different stations (Ex. Create a station for just blue litmus paper with all the solutions already present. Each pH indicator can be in its own station.)

·         Differentiation: Teachers may or may not have students use pH to calculate the H⁺ and/or the OH^- ions in solution.

For the Student

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