2. What type of bonding allows water to attract other water molecules? 3. What is the difference between solutions and mixtures?

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Bertina Bridges
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1 Biology Lab Name(s) Period: Date: Purpose: To investigate the properties of water, ph, and enzymes that biologically impact biological functions. Background Information: Water: Sometimes we call water H2O. That s because water molecules have two hydrogen atoms and one oxygen atom. While water molecules are neutral charged as a whole, water molecule tends to have an uneven distribution of electron density giving it a positive charge end near the hydrogen while the other end has a negative charge near the oxygen. This chemical property is called polarity. The ability of ions (products made from ionic bonds) and other molecules (products made from covalent bonds) to dissolve in water is due to polarity. In addition, each end of a water molecule is attracted to the opposite charged end of another water molecule. This is called hydrogen bonding. Due to hydrogen bonding, water exhibits the following properties of cohesion and adhesion. Cohesion is the attraction of water molecules to other molecules. It is the result of hydrogen bonding the attraction of the hydrogen atoms in water to the oxygen atoms in water. It is the property that allows water droplets to form. Cohesion is responsible for surface tension. This property allows some insects to walk across water. Adhesion is the ability of water to stick to other surfaces. For example, water forms on mirrors in a steamy bathroom. Adhesion is a property that causes water to be drawn up through soil and into paper towel. When water is drawn up through small spaces, it is called capillary action. Lastly, due to hydrogen bonds holding water molecules further apart in a solid state than in a liquid state, water is less dense and floats. Water is an amazing substance that is critical to life. It serves a purpose in various processes such as cellular metabolism, heat transfer, structural support and universal solvent (liquid). For these reasons and more, the presence of water is a good indicator that life may be sustainable in certain environments, such as the Jovian moon of Europa. Liquids: A liquid substance that has a group of molecules (solute) evenly distributed in a solvent (water), it is a solution. When a solution is favors one concentration over another, it is a mixture. ph: A solution can range from acidic to basic. The ph scale measures how acidic or basic a substance is. The ph scale ranges from 0 to 14. A ph of 7 is neutral. A ph less than < 7 is acidic (more H+ are present). A ph greater than >7 is basic (more OH- are present). The more hydrogen ion (H+) or hydroxide (OH- ), the more likely a compound or ion will react in a solution. Distilled water tends to be neutral. But when chemicals are mixed with water, the mixture can become either acidic or basic. A solution may be an acid, base, or neutral. The degree of acidity or basicity can be measured using the ph scale. The scale is divided into three areas: acid (0-6.5 ph), base ( ph), and neutral (7 ph). Each division either increases or decreases the ph (concentration of H+ or OH) of a substance ten times (10x). Example would be, the ph of 4 is (10X) more acidic than a ph of 5. Water has a ph of 7 but when it mixes with air, the suspended materials will either raise or lower its ph. Acid rain is an example of this type of reaction. Enzymes: Potatoes contain the enzyme catalase, which breaks down hydrogen peroxide formed in the cells causing bubbles of oxygen gas to be released. Seeing bubbles is a sign that a chemical reaction is happening. Temperature, ph, and the amount of enzyme all affect reaction rate, or how fast a reaction happens. Part B will be testing temperature and ph. If an enzyme, which is made of proteins, gets too hot or cold, it can change the shape of the enzyme, or denature the enzyme, so it will not work. Also, if an enzyme is at the wrong ph, it will not work. This is the reaction when Hydrogen Peroxide is broken down by the enzyme catalase within cells. 2H 2O > 2H 2O + O 2 Warnings: Keep droppers and graduates clean - don t mix chemicals or droppers! Report spills immediately. Wear safety goggles throughout the lab! Do not touch any of the chemicals or indicators, USE THE DROPPERS! Pre- Lab Questions: answer before the lab 1. Describe polarity. 2. What type of bonding allows water to attract other water molecules? 3. What is the difference between solutions and mixtures?

2 4. ph is measured on a scale of to. 5. Acids contain an excess of H+ and will measure between &, while bases contain an excess of OH- and will measure between &. 6. A ph measure of 7 is. 7. Each division of ph represents the concentration of H+ or OH-. 8. What type of macromolecule are enzymes? 9. Describe the function of enzymes. 10. Write the reaction for the break down of hydrogen peroxide and label the products and reactants. 11. Identify 3 things that affect the rate of a chemical reactions? Part A: Penny Drop Question: How many drops of water will a penny hold? Hypothesis: I think a penny will hold drops of water. I think a penny will hold drops of soap water Materials: Penny, Eyedropper, Water Procedure: 1. Put the penny on a flat surface. 2. Use the plastic droppers to drop water on the penny, one drop at a time. 3. Count the number of drops until the water spills over the edge of the penny. 4. Record your data. 5. Repeat steps 1-4 for a total of 4 trials. 6. Repeat steps 1-4 for the water containing soap. (USE DIFFERENT PLASTIC DROPPERS) Data Number of drop of water held by a penny Solution Water Soapy Water Trial Number of Drops Average

3 Data Analysis: 1. Did you get the exact same data each time you performed the investigation for each type of solution? What are some possible sources of data inconsistency 2. How do your results compare to the other groups in your class? Provide at least 2 possible reasons for any similarities and differences you identified. Analysis: 3. Why did the water without soap not diffuse when you initially dropped it on the penny? Explain. 4. How do your results models the water properties of adhesion and cohesion. Why would you expect there to be a difference in the number of drops your can hold on your penny with water and soapy water? Explain. 5. Considering the concept of surface tension. Why is it dangerous to jump from a high elevation on to still water? Explain. 6. How do the chemical properties of water impact metabolic reactions? (Consider the impact of soap on hydrogen bonds)

4 Part B: ph Lab Materials: ph paper Staining Trays Lemon Juice Distilled Water Hydrogen Peroxide (H2O2) Glass Cleaner (Windex) Vinegar 409 Cranberry Juice (Fermented) Tap Water Lemon Juice with Antacid (Tums) Procedure: 1. Using ph scale identify the ph of the samples provided. 2. Use the staining trays to test each drop on ph indicator. 3. Put a drop of solution on each slip of ph indicator paper as listed below: CAUTION do not come in contact with any of the materials. If contact is made, wash it off under running water. 4. Observe for 1 minute for the indicator to give a stable reading. 5. Use the ph scale provided to determine the ph number. Write this on your chart. 6. Identify if it is acid, base, or neutral. 7. Visualize whether the liquid is a mixture or a solution 8. Record this observation on the data table on the next page (data chart). 9. Repeat the procedure for the rest of the solutions. Data: Table B: ph Observations Substance Color of ph paper ph Acid/Base/Ne utral Solution or Mixture 1. Distilled Water (Brown Dropper) Solution ANALYSIS: 1. Which of the liquid would you identify as a mixture? Why?

5 2. If the ph of a sample was 4, how MANY MORE TIMES acidic is it than a solution with a ph of 6? 3. If the ph of a sample were 11, how MANY MORE TIMES basic (alkaline) is it than a solution with a ph of 8? 4. How might one correct the ph of a lake with a reading of 3? (hint: what could you add?) 5. Why would stomach acid (gastric acid) with a ph between be beneficial? Explain. 6. Why would blood vessel with an slightly alkaline ph (7.35 to 7.45) be beneficial? Explain. 7. If skin has the ph of 5.5, which liquids would impact the skin cells survival slowly? Immediately? Why? 8. Which liquid(s) would erode your tooth enamel (>5.5) if you consumed it periodically? 9. Draw lines and label where your samples would be on the ph chart below. Acid Neutral Base

6 Part C: Reaction Rate of the Enzyme Catalase Material Needed: Test tubes, test tube rack, medicine droppers, ph papers, safety goggles, 0.1 M NaOH, acid, water, 0.1 M hydrochloric acid, 3% hydrogen peroxide, cooked potato, uncooked potato, Hypothesis: Make a hypothesis about what happens to a potato as it s temperature or ph change Procedure: 1. Put on safety goggles. 2. Number your test tubes 1-3 (This may already be done for you.) Use clean droppers and spatulas to put the following in the flasks. Caution: Don t touch sodium hydroxide (NaOH), it is a strong base! Flask 1 one pinch (4-5 mini pieces) of uncooked potato Flask 2 - one pinch cooked potato Flask 3 - one pinch of uncooked potato + 5 drops of sodium hydroxide 3. Gently swirl flask 3 to mix the potato with the NaOH and then wait 30 seconds before step Using a dropper, add 15 drops of hydrogen peroxide to flasks 1, 2, and 3. Look for bubbles (it may take a minute or more for bubbles to appear). Identify the bubble activity in each flask by assigning it a number from = no bubbles 1= few bubbles 2= moderate bubbles 3= many bubbles Record bubble activity on data table B 6. Clean up the materials for this part of the lab! Dump all potato products and chemicals in the waste container. Wash out your test tubes in the sink and put them upside- down to dry in the test tube rack. Make sure all used ph paper is thrown away. Data: Table C: Enzyme Activity Test Tube Type 1 potato 2 Cooked potato Bubble Level Which potato type had more bubbles? What is the ph of NaOH? (hint: see part B) Which test tube acts as your control in this test? 3 Potato in base (NaOH) Key: 0 = No bubbles 1 = Few bubbles 2 = Moderate bubbles 3 = Many bubbles Conclusion: (HINT: reread background information for help with answers) 1. What happened when you added hydrogen peroxide to test tube 1? What does this mean? 2. What is the name of the enzyme that caused the bubbles of oxygen gas to be released?

7 3. Why did the potato enzyme not work in the cooked potatoes in tube 2 (there were no bubble, why? Explain in great detail)? 4. What was the enzyme activity like in tube 3? Why was it different than flask 1? 5. Summarize your results: What is needed for the enzyme to work as it should? Conclusion: On the back of this paper, write a conclusion for the 3 lab. Summarize your findings and analysis. * Everyone must write their own conclusion, so if you are sharing a lab paper, you will need to staple two conclusions to the lab before turning it in. Include the following (1 sentence for each): What did you learn about macromolecules (larger molecules)? What did your learn about water? What did you learn about ph? What did you learn about enzymes? What hypothesis did you make and explain if you were right or wrong. Did anything go wrong and what? How could you improve these labs? What did you like or not like about the lab? Quiz Review: Review your chapter terms, lab, homework questions. In the book, condensation is synthesis (building polymers from monomers) and hydrolysis is digestion (breaking polymers from monomers). Concept Focus Chemical Bonding Properties of Water Macromolecules

The Water Molecule. Like all molecules, a water molecule is neutral. Water is polar. Why are water molecules polar?

The Water Molecule. Like all molecules, a water molecule is neutral. Water is polar. Why are water molecules polar? Properties of Water The Water Molecule Like all molecules, a water molecule is neutral. Water is polar Why are water molecules polar? Polarity oxygen atom 8 protons in its nucleus has a much stronger attraction