Cabbage Juice pH Indicator Lab

Lemon Juice Acidic Neutral Basic Baking Soda Acidic Neutral Basic Shampoo Acidic Neutral Basic Windex (Ammonia) Acidic Neutral Basic Milk of Magnesia Acidic Neutral Basic Sour Candy Acidic Neutral Basic Vinegar Acidic Neutral Basic Making the pH Indicator (this can be done in advance): 1. Put the red cabbage leaves into the blender with 800 mL of water. 2. Close the top and let it blend at high power for 30 seconds. 3. Pour the mixture through a strainer into a large container. (This should provide you with 600-800 mL of cabbage juice.) Testing pH: 1. Pour 1 Tbsp of each individual liquid into its respective cup (except for baking soda). 2. For baking soda, add 1 tsp of baking soda into 2 tsps water. 3. Pour 1 Tbsp of cabbage juice into each of the cups, swirling gently. Q8. Write down what color each solution turns the cabbage juice, based on the following pH scale. Liquid Color pH Water Violet 6 Lemon Juice Red 2 Baking Soda Blue 8 Shampoo Purple 6 Windex (Ammonia) Blue-Green 10 Milk of Magnesia Blue 10 Sour Candy Red 2 Vinegar Purple 4

Although the math isn’t very straight-forward for weak acids and bases, you can actually calculate the volume of strong acid needed to neutralize a strong base, and vice versa, using the formula below. Acid volume x Concentration of ions in acid = Base volume x Concentration of ions in base Q16. If I have 1 volume of a strong acid at pH 5, how much of a strong base at pH 10 would I need to get to a neutral pH? A pH of 5 is 2 away from 7, so it has 100 hydrogen ions. A pH of 10 is 3 away from 7, so it has 1,000 ions. You need an equal number of H+ and OH- to reach a neutral pH. Concept Questions Q17. Look at the list of things which have very acidic pH’s. What do these substances have in common? Can you think of other foods that probably also have acidic pH’s? All items in the list of very acidic pH’s have a decent level of sourness to them. Other foods that may have acidic pH’s based on this are oranges, limes, and tomatoes. Q18. Fats and oils (like butter, vegetable oil, or even the oil on your skin!) can react with the OH - ions in bases and feel “slippery” or “soapy.” Can you think of instances where that property would be useful? What kinds of things do you think basic products would be useful for (besides neutralizing acids)? That property can be useful in cleaning supplies. Cleaning supplies are useful for removing oils from counters, our skin, and other surfaces. Q19. Stomach acid has a pH of about 2. Normally the stomach protects itself by producing a slippery substance that’s resistant to the acid, but sometimes it breaks down. What do you think happens? Do you know what this is called? How could you reduce the amount of acid (think of things that we tested!)? If the substance in the stomach that resists acid breaks down, the acid may begin to break down the lining of the stomach. This can cause indigestion. You could reduce the amount of acid by neutralizing it with a very basic substance like milk of magnesia.