How Do Plants on Earth Affect the Amount of Carbon in Earth’s Atmosphere

Student Exploration: pH Analysis Vocabulary: acid, acidic, alkaline, base, indicator, neutral, pH Prior Knowledge Questions (Do these BEFORE using the Gizmo.) 1. Acids are substances that produce hydrogen ions (H+) when dissolved in water. Lemon juice is an example of an acid. A. B. What does lemon juice taste like? Sour What does it feel like if lemon juice gets in your eye? Stinging feeling, irritated 2. Bases are substances that produce hydroxide ions (OH-) when dissolved in water. Hand soap is an example of a base. A. What does soap feel like? Slippery, clean, foamy B. What does soap taste like? Bitter taste C. What does it feel like if soap gets in your eye? Burning sensation Gizmo Warm-up The strength of an acid or base is measured on the pH scale. The term “pH” is short for “potential of hydrogen.” It is a measure of how many excess H+ ions there are in a solution. The pH scale runs from 0 to 14, with 0 representing the highest concentration of hydrogen ions. Acidic substances have a pH below 7, while alkaline substances (bases) have a pH above 7. Pure water has a pH of 7 and is considered neutral. The pH Analysis Gizmo allows you to find the pH of a variety of liquids. In the Gizmo, check that the Substance in the tube is Ammonia, and click Test. Wait until the animation is finished. 1. Indicators change color in acids or bases. What is the color of the pH paper? Blue 2. Compare the paper to the pH color chart. What is the pH of ammonia? 11 3. Is ammonia acidic or alkaline? Alkaline/base Activity A:  Click Reset.  Check that the 0-14 paper is selected. Measuring pH Goal: Find the pH of 18 common substances. 1. Test: Use the Gizmo to find the pH of each of the available substances. Classify each substance as acidic (pH < 7), alkaline (ph > 7), or neutral (pH = 7). 0-14 pH indicator paper Material in the tube pH value Baking soda 8 Acidic, alkaline, or neutral? Alkaline Bleach 11 Alkaline Coffee 5 Acidic Cola 2 Acidic Drain cleaner 13 Alkaline Hand soap 10 Alkaline Juice (lemon) 2 Acidic Juice (orange) 3 Acidic Juice (tomato) 4 Acidic Milk 7 Neutral Milk of magnesia 10 Alkaline Alkaline Oven cleaner 13 Saliva (human) 6 Acidic Shampoo 6 Acidic Stomach acid 1 Acidic Vinegar 4 Acidic Water (distilled) 7 Neutral Water (ocean) 8 Alkaline 2. Summarize: Compare all the acidic substances and all the alkaline substances. In general, what types of substances tend to be acidic? ISH acidic substances have a slightly sour taste and A. B. What types of substances tend to be alkaline? they tend to be more slippery like, soap, oven cleaner Activity B: More accurate pH  Click Reset.  Select the 4.5-7.5 paper. Goal: Find the pH of substances in a more accurate way. 1. Test: Before you begin testing with the 4.5-7.5 paper, list the pH values of the substances below that you found using the 0-14 pH indicator paper. Then find the pH of each substance with the 4.5-7.5 paper. 4.5-7.5 pH indicator paper Material in the tube pH value (0 to 14 paper) Coffee 5 pH value (4.5 to 7.5 paper) 5 Milk 7 6.5 7.5 Oven cleaner 14 Saliva (human) 7 6.5 Shampoo 6 5.5 Stomach acid 1 4.5 Water (distilled) 7 7 2. Analyze: Compare the pH values in each column. A. How do these values compare? the values are almost similar B. What is an advantage of using the 4.5-7.5 paper? lower acidic and alkaline range C. What is a disadvantage of using the 4.5-7.5 paper? The range is too small for some of the values. D. Given the results from two kinds of indicator paper, which substances appear to be neutral (pH = 7)? milk or distilled water or shampoo