Measuring the pH Level in Household Substances Using Red Cabbage Juice as the pH Indicator

Jocelyne Cortes

Mrs. La SalleChemistry/Period 35/28/2013

PURPOSE

To experiment and gain knowledge about calculating pH values in different substances.

MATERIALS

(1) Knife Sliced Red Cabbage Leaves (1) 1-cup Measure (1) Pot of Hot Water (2) Jars (1) Clean White Cloth (1) Teaspoon (1) Roll of Tape (3) Sheets of Blank White Paper (1) Black Marker (1) Ruler (1) Spoon (10) Clear Plastic Cups White Vinegar Baking Soda Household Ammonia (Windex) Other Household Items

-Salt, Milk, Dish Detergent, Mouthwash, Toothpaste, Shampoo, All-Purpose Household Cleaner

PROCEDURES

Step 1: Make sure all the red cabbage leaves are chopped up. Measure about 2 cups of the chopped up red cabbage and pour it all into the first available jar. Next, pour 2 cups of hot water into the jar as well. Next, grab the spoon and stir/crush the red cabbage juice in the hot water until a solid dark blue color has established. With the white piece of cloth, place it over the second jar and grab the first jar and carefully pour the substances from the first jar into the second. This is basically straining the extract away from the liquid which is the pH indicator liquid.

Step 3: Next, make a pH scale. Tape the three pieces of paper together (the hotdog way). Draw a straight line horizontally through the middle all three pieces of paper. Now measure 5 cm from left to right and for every 5 cm draw a line, that line will represent a pH value. The pH scale should be 1-14.

Step 4: Set up all 10 plastic cups and label them with the household substance whose pH will be evaluated. (Salt, Vinegar, Baking Soda, Toothpaste, etc.) Next, for each empty cup, place about 1 cm worth of the cabbage pH indicator. Now, depending on what the cup is labeled, drop a small amount of each labeled substance into the cup, mix, and observe the change in color that occurs. Repeat until all substances have been tested.

VinegarBaking Soda

Ammonia

…MORE HOUSEHOLD ITEMS TESTED

Cleaner

Soap

Step 5: Based on the result of color, attempt to correctly align them on the pH scale from base to acid (1-14).

RESULTS

•DISHWASHER DETERGENT: 1•TOOTHPASTE: 2•VINEGAR: 3•MILK: 4•MOUTHWASH:5•ALL PURPOSE HOUSEHOLD CLEANER: 5•SHAMPOO: 6•CABBAGE JUICE (INDICATOR): 7•SALT: 7•BAKING SODA: 9•WINDEX: 11

ANALYZE AND CONCLUDE QUESTIONS (PG 604)

The color of the indicator in Acidic Substances: Lighter colors. For instance, the

Dishwasher Detergent was bright yellow (estimated pH of 1) and the Vinegar turned to be a light hot pink (estimated pH of 3).

Neutral Substances: The natural color of cabbage which was a solid blue. The salt also turned our to be that exact shade of deep blue. They’re pH was estimated to be a neutral 7.

Basic Substances: These tended to be on the darker side, for example the ammonia with an estimated pH of 11 was a dark green. Baking soda can be guessed to have a pH of 9 and its color was a very dark bluish green.

The chemical changes responsible for the color change was in the red cabbage juice indicator because its hydrogen ion concentration changed when a test substance was added to it. Acids produce hydrogen ions in aqueous solution. Bases contain hydroxide ions. A substance is neutral because of equal numbers of hydrogen and hydroxide ions

Results for materials tested:•DISHWASHER DETERGENT: ACID•TOOTHPASTE: ACID•VINEGAR: ACID•MILK: ACID•MOUTHWASH: ACID•ALL PURPOSE HOUSEHOLD CLEANER: ACID•SHAMPOO: ACID•CABBAGE JUICE (INDICATOR): NEUTRAL•SALT: NEUTRAL•BAKING SODA: BASE•WINDEX: BASE

The group that contains items used for cleaning or personal hygiene are the acids. For example, toothpaste, mouthwash, and shampoo were all found to be acids.

Based on my results, I can confidently say I mastered the purpose of this lab. I was able to understand not only the differences between acids and bases but also comprehend how hydrogen and hydroxide concentrations are the what affect whether a substance will be a base or acid. The aspect that makes me question my certainty of this lab is how on the Dishwasher Detergent, I might have placed it in the wrong section. I now believe that it should have had a pH of around 4, but I feel as though my error occurred when the color of pH came for milk. It was such a peculiar color that it just through off my entire placing. Overall, the rest of my results comply with the purpose in the sense that they correctly describe the expected pH of that substance.

Conclusion