We use the pH scale to test the level of acidity in substance. Litmus paper is used to to test the pH. Acids will turn the paper pink, and bases will turn the paper blue. Acids are considered to have pH greater than 7, neutral is considered 7 and bases are considered anything less than 7.
Acids are sour foods
Neutrals are water or milk
Bases are bitter like soaps
- Measure 30 mL of vinegar into a cup
- Use a cotton swap to dab vinegar onto red litmus paper and onto the blue litmus paper. Observe the color of the wet paper and record it on the date table.
- Indicate on the table whether the vinegar is acidic or basic.
- Add 1/8 teaspoon of the baking soda solution to the plastic cup. Swirl for about 1 minute. Indicate on the data table whether bubbles formed or not. If bubbles are present, continue to swirl the cup until no more bubbles form.
- Use a CLEAN cotton swab to transfer a small account of the contents in the plastic cup onto the litmus (both red and blue). Pick a dry spot. Observe the color of the wet paper and record it onto the data table. Indicate on the table whether its acidic or basic.
Students should be able to state whether vinegar and baking soda are acidic or basic.
Purpose: to show how you can take an acid and add a base to make it a neutral solution.
Introduce: Taste tests!
Difficulties: measurement issues
Changes: pre-measureing things for students.