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Determining pH of Household Items
- 1. Determining pH of Household Items Teaching Strong/Weak Acids and Bases through Inquiry and Observation Auburn R. James
- 2. Applying Major Units in Chemistry to Everyday Life Acids Bases Salts -soda -soap -table salt -clothing dye -cleaning supplies -pool treating supplies -stomach acid -toothpaste -baking soda Encountered in Everyday Life http://whatafy.com/who-discovered-sulfuric-acid.html http://www.pacoa.com/austin-521-clear-ammonia-00052.html http://www.amerimerc.com/pool-chlorine~granular-chlorine.htm
- 3. Active Participation Throughout Acid/Base/Salt Units Students are asked to Students identify why they Material is tested. bring items from home that hypothesize this material The pH is determined they think are classified as falls into that catergory using a probe, reactivity an acid, base or salt (each (cleaning supplies with chemicals is unit can focus on one of containing ammonia feels compared to that of known the categories) soapy, soda tastes acidic) acids/bases and salts. What did the student learn Calculations are through observation? performed—what is the Were they right? What is pKa of the acid in Coke? the identity of the chemical Results are written up and in the item they brought presented, in?
- 4. Highlights of Lesson, Why is it Engaging? Students are required to think about materials’ properties to decide Observe and which to bring in compare Applies properties of science to household items everyday to laboratory life chemicals Hands on laboratory study Practice Identify substance using pH by data collected: probes data processing and calculations Lesson supports group work http://www.geminibv.nl/labware/metrohm-704-ph-meter-1/
Editor's Notes
- This theme applies the ideas of strong/weak acids, bases and salts to every day life. Several months are spent addressing these topics and this can be a weekly activity throughout all three units (strong acids/bases, weak acids/bases, and salts).
- Not only do students encounter acids, bases and salts in every day life, they use those properties of those items for their benefit. Common characteristics of these items can help students identify them without litmus paper or a pH meter: acids have a bitter taste, bases feel soapy, salts are compound solids. Given these “hints” and basic street knowledge, students should have an idea of common household items that fit into these categories.
- At the beginning of each unit, students will be asked to bring in items from home that they believe qualify under that week’s category. One week can be acids, one bases, etc. Students will have to use inquiry and think about the items they encounter in every day life and determine what qualifies for the category and why they think the item is in that category. In class, the items will be tested to determine their identitfy as a weak or strong acid or base or a salt. The pH will be determined, the item can be titrated against a strong acid or base (the opposite of what it is), the reactivity can be determined. The student will state whether or not their hypothesis was correct, and if not, what false assumption they had. For instance, say one week students are asked to bring in acidic salts. A student brings table salt because they believe it tastes bitter. Results show table salt as a neutral salt. The student will understand why their assumption was incorrect. Finally, students will perform the calculations learned in class to determine the pKa and Ka of the material. The pKas can be compared to known chemicals to determine the identity of the material, if unknown. The students may work in groups and may present results to the class and write laboratory reports of their results.
- This lesson is engaging and creates ownership for the students as they are responsible for thinking about the uses of chemistry in their lives and hypothesizing materials that have chemical characteristics and bringing them in from home. Titrations performed on laboratory chemicals are given real meaning when compared to the titration curve of an item brought from home. The uses of materials can be explained based on their identity as an acid, base or salt. In this narrative, students obtain practice using laboratory equipment in a way that is meaningful and interesting to them. Students will have invested interest in their hypothesis being correct, however would not lose credit for this assuming they accurately explain the classification of their item. Chemicals can be identified by their pKa’s, this experiment can lead to the identification of the unknown acid, base or salt in the material. Not only is the lesson fun and interesting, but it incorporates important graphing and calculations as well as writing and public speaking with the lab report and presentation components. Students may work in groups in case someone forgets to bring an item in and so multiple items are tested and compared.