Testing the pH of household liquids is a simple way to see chemistry in everyday life. pH tells how acidic or basic a liquid is, which affects taste, cleaning power, safety, and reactions with other substances. In this project, students compare 10 common liquids such as lemon juice, vinegar, water, soap solution, and diluted ammonia using pH strips or red cabbage indicator. The goal is to collect evidence, organize results, and connect colors on an indicator to acidity and basicity.
Key Facts
- pH = -log10[H+], where [H+] is the hydrogen ion concentration in moles per liter.
- Acids have pH less than 7, neutral solutions have pH about 7, and bases have pH greater than 7.
- Each 1 pH unit change means a 10 times change in hydrogen ion concentration.
- Common examples: lemon juice pH 2, vinegar pH 3, pure water pH 7, soap solution pH 9 to 10, ammonia solution pH 11 to 12.
- Red cabbage indicator turns reddish in acids, purple near neutral, and green to yellow in bases.
- Never mix household chemicals, especially bleach, ammonia, drain cleaner, or strong cleaners, because dangerous gases or heat can form.
Vocabulary
- pH
- pH is a number that shows how acidic or basic a water-based solution is.
- Acid
- An acid is a substance that increases hydrogen ion concentration in water and usually has a pH below 7.
- Base
- A base is a substance that lowers hydrogen ion concentration in water and usually has a pH above 7.
- Indicator
- An indicator is a material that changes color depending on the pH of a solution.
- Control
- A control is a standard sample used for comparison, such as distilled water with pH near 7.
Common Mistakes to Avoid
- Dipping the same pH strip into multiple liquids, which contaminates samples and makes the colors unreliable. Use a fresh strip or clean dropper for each liquid.
- Reading the strip color too late, which can give a changed or faded result. Compare the strip to the color chart at the time listed on the package.
- Assuming red cabbage indicator gives an exact pH number, which is wrong because it usually gives a pH range. Use pH strips or a pH meter for more precise values.
- Testing strong cleaners without safety steps, which is unsafe because some liquids can burn skin or produce harmful fumes. Wear goggles, use small amounts, dilute when instructed, and never mix cleaners.
Practice Questions
- 1 A vinegar sample has pH 3 and a soap solution has pH 9. How many times greater is the hydrogen ion concentration in the vinegar than in the soap solution?
- 2 A student records pH values for 10 liquids: 2, 3, 4, 6, 7, 8, 9, 10, 11, and 12. How many samples are acidic, neutral, and basic?
- 3 A red cabbage indicator turns pink in lemon juice, purple in water, and green in baking soda solution. Explain what these colors show about the relative pH of the three liquids.