BIOL 102: Lab 2

Solutions, Acids and Bases

PRE-LAB ASSIGNMENT:

Students are expected to read pages 1 to 3 before coming to the lab to complete the experiments.

Print this entire lab packet and bring it to the laboratory. You must submit the completed lab worksheet for credit. Please provide a FULL lab report for this experiment.

Objectives:

After completing this laboratory assignment, students will be able to:

· Measure the pH of various liquids.

· Demonstrate that buffers stabilize the pH of a liquid.

· Measure the ability of commercial antacids to buffer the pH of a liquid.

Acids:

Acids are ionic compounds (compounds with a positive or negative charge) that break apart in water to form hydrogen ions (H+). The strength of an acid is based on the concentration of H+ in the solution.

The greater the concentration of H+, the stronger the acid.

1

1

1

Characteristics of Acids:

· Acids taste sour.

· Acids react strongly with metals (Zn + HCl).

· Strong acids are dangerous and can burn your skin.

Examples of Acids:

· Vinegar

· Stomach Acid (HCl)

· Citrus Fruits

Bases:

Figure 1: Hydrochloric acid (HCl) in water

Bases are ionic compounds that break apart to form a negatively charged hydroxide ion (OH-) in water. The strength of a base is determined by the concentration of hydroxide ions (OH-). The greater the concentration of OH-, the stronger the base. Solutions containing bases are often called alkaline .

Characteristics of Bases:

· Bases taste bitter.

· Bases feel slippery.

· Strong bases are very dangerous and can burn your skin.

Examples of Bases:

· Sodium hydroxide (lye)

· Ammonia

Figure 2: Sodium

Hydroxide (NaOH) in water

pH Scale and Indicators
The strength of an acid or a base in a solution is measured on a pH scale. The pH scale is a measure of the hydrogen ion (H+) concentration. It spans from 0 to 14 with the middle point (pH 7) being neutral (neither acidic nor basic). Any pH number greater than 7 is considered a base and any pH number less than 7 is considered an acid. 0 is the strongest acid and 14 is the strongest base. An indicator is a special type of compound that changes color as the pH of a solution changes, thus telling us the pH of the solution.

Figure 3: A pH scale indicating the pH of common substances.

Measuring pH
A convenient way of measuring the pH of a solution is with pH paper. pH paper is treated with a chemical indicator that changes color depending on the concentration of H+ in the solution that it has contacted. The color chart on the container of the pH paper is used to compare the color of the pH paper to determine the pH of the solution (see Table 1).

Table 1: Examples of pH indicators.

Indicator

Range

Color Change

Methyl violet

0.2 – 3.0

Yellow to blue-violet

Bromphenol blue

3.0 – 4.6

Yellow to blue

Methyl red

4.4 – 6.2

Red to yellow

Litmus

4.5 – 8.3

Red to blue

Bromcresol purple

5.2 – 6.8

Yellow to purple

Phenol red

6.8 – 8.0

Yellow to red

Thymol blue

8.0 – 9.6

Yellow to blue

Phenolphthalein

8.3 – 10.0

Colorless to red

Buffers
Buffers are mixtures of two chemicals that stabilize the pH of a solution by resisting changes in the pH.

· If the pH is too low, one chemical will bind some of the hydrogen ions and raise the pH.

· If the pH is too high, the other chemical will donate some hydrogen ions to lower the pH.

pH in the body
The blood pH must be maintained very close to 7.4 which is slightly alkaline. A change of 0.2 pH units in either direction is considered dangerous and potentially fatal. Hydrogen ions are extremely reactive and affects many molecules which regulate physiological processes.

The body regulates pH in several ways including eliminating CO2 by the lungs and eliminating other acids and bases by the kidneys. The most important way to minimize pH changes in the body is using buffers. All body fluids, inside or outside of the cells, have buffers which defend the body against pH changes. The most important buffer in extracellular fluids, including blood, is a mixture of carbon dioxide (CO2) and bicarbonate anion (HCO3). CO2 acts as an acid because it forms carbonic acid when it is dissolved in water and donates hydrogen ions when they are needed. HCO3 is a base, soaking up excess hydrogen ions. There are also other buffers in the blood, such as proteins and phosphates, but they are less important in maintaining the overall pH of the blood. Blood pH is established by a balance between bicarbonate and CO2.

LAB DATASHEET
Exercise 1: Determining the pH of common substances
1. Use pH paper to measure the pH of the following liquids.

2. Be as accurate as possible

3. Use a fresh piece of pH paper or pH dipstick for each test.

4. Record your data.

Baking soda

___7____________

0.1M HCl

___0____________

Vinegar

___2____________

Tap water

___6___________

Seltzer water

___5____________

Exercise 2: Testing the buffering capacities of various solutions
1. Obtain and label four test tubes according to the four solutions listed in Table 2.

2. Place 5 ml of each solution into its appropriately labeled tube.

3. Measure the pH of each of the solutions in the tubes and record these initial values in Table 2.

4. Add 5 drops of acid (0.1 M HCl) to the first tube. Cover the tube with parafilm and invert the tube gently to mix the contents.

5. Measure the pH of the acidified solution and record it in Table 2.

6. Repeat steps 4 and 5 for each of the remaining tubes. Record your results in Table 2.

7. Compare the initial pH and the pH after acid addition for each sample.

Table 2: Buffering Capacity Data

Solutions

Initial pH

Final pH (after HCl)

Comparison of pHs

Water

5

2

PH dropped by 3

0.1 M NaCl

5

3

PH dropped by 2

Skim milk

6

5

PH dropped by 1

0.1 M phosphate buffer

7

7

PH stayed the same

Analysis Questions:

1. What is the biological importance of using a buffer?

Buffers prevent changes in PH, and maintain balance.

2. Which of the solutions is the most effective buffer? Least effective?

The most effective buffer is the solution who’s PH changed less, (in this case will be 0.1M phosphate buffer). The least effective solution will have a significant change in PH (in this case it will be H2O with an original PH of 5, and a final PH of 2 after addition of 0.1M of HCL)

Exercise 3: Testing the effectiveness of commercial antacids and other products
Commercial antacids such as Alka Seltzer, Rolaids, and Tums claim to “neutralize stomach acid” by absorbing excess hydrogen ions (produced as hydrochloric acid in the stomach).

To test the abilities of these products to absorb acids, do the following:

1. Using a pipet or 10 mL graduated cylinder, add 1 ml of the antacid solution to a test tube.

2. Add 1 drop of the indicator Bromcresol purple to the tube.

3. Cover the tube with parafilm and invert the tube to mix the contents.

4. Add one drop of 0.1 M hydrochloric acid (HCl) to the tube; mix after each drop.

a. Continue this process until the solution turns yellow, indicating an acidic solution.

5. Record the number of drops of acid needed to generate the change of color.

a. This number of drops is an index to the amount of acid (H+) that the solution neutralizes before the pH drops below the yellow end-point of Bromcresol purple.

Table 3: Effectiveness of Antacids Data

Antacids

Drops of Acid

Alka – Seltzer

33

Rolaids

1

Tums

1

Analysis Questions:

1. Which antacid neutralizes the acid best? Which neutralizes the acid least?

Rolaids and Tums neutralized acid best while Alka-Seltzer neutralized acid the least.

2. Examine the package of the products you tested. What are the active ingredients of each product?

Tums – Calcium carbonate 50mg

Rolaids – Calcium Carbonate

Alka- Seltzer – Aspirin 325mg, citric acid 1000mg, and sodium bicarbonate 1916mg

 

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1. Read the course textbook’s chapter on cell division, specifically the last section on how cells become cancerous. This is context for completing Individual Assignment 3.

2. Watch the Presentation in Module/Week 9 entitled “Ways to Fight Cancer.” Notice that the presentation outlines essentially 3 approaches to fighting cancer: a) reduction of cancer risks, b) correction of cancer genes, and c) destruction of cancerous tissue.

3. Open the “10 Discoveries in the War on Cancer” document in the Assignment Instructions folder. Scan the discoveries briefly. Then, open the assignment submission link in Module/Week 9. In the text box, number from 1 to 10 for the 10 discoveries.

4. Reflect carefully on discovery 1. Would this discovery be more useful for a) reducing cancer risks, b) correcting/restoring cancer cells to normal, or c) destroying cancerous tissue? After number 1 in your list, place in parentheses the letter representing the approach to fighting cancer that will best be served by this new discovery. (More than 1 approach may be served, but which is most likely to be helped most significantly?)

5. Repeat this analysis for each of the remaining 9 discoveries. Return to the “Ways to Fight Cancer” presentation as needed for additional perspective. When finished, your entire text box must be simple: a numbered (1-10) list of letters (a), (b) or (c). The assignment is now complete.

6. Each correct association up to 8 correct answers is granted 7 points. If you get 9 or 10 out of 10, you get a perfect score (60 pts.) on the assignment.

Submit this assignment by 11:59 p.m. (ET) on Monday of Module/Week 9.

BIOL 101

Individual Assignment 3 – 10 Discoveries in the War on Cancer

1. Virologists are modifying lentiviruses as vectors for carrying proto-oncogenes into cancer-transformed cells in culture. They are developing this virus for inserting the ras proto-oncogene directly into its correct location in the genome. The correct ras gene will already be linked to human DNA on either side of it and complexed with a recombination enzyme that will insert it into its correct location within the human genome. At the same time, the recombination enzyme will excise the defective oncogenic form of ras. The cells in culture should again come under normal hormonal control and require extra-cellular signals in order to continue dividing.

 

2. Malignant brain tumors in adults are fast-growing cancers with median survival rates of 15 months, even with aggressive treatment. Researchers have been searching for genetic “signatures” (characteristic groups of cancer-causing genes) that could help in defining the kind of brain tumor the patient has. They hope to be better able to predict the course of the disease and more accurately design the patient’s course of treatment.

 

3. Tobacco smoking is the leading cause of preventable deaths worldwide. It is a risk factor for lung cancer and several other types of cancer. Results of analysis of the entire human gene collection (the “genome”) support some previous findings that a region of human chromosome number 15 contains one or more genes that are associated with smoking intensity (the number of cigarettes smoked per day) and the closely related trait of nicotine dependency. Scanning people’s genomes for these genes will help them to determine their risk of addiction should they begin smoking tobacco.

 

4. Immunologists are working with a mutation (HER2) that is expressed on the surface of many breast, bladder, pancreatic, and ovarian cancer cells. They have made antibodies against this mutant surface protein. These antibodies have been covalently bonded to a “gene expression vector” that makes cells light up when incubated with luciferin from fire flies. The vector takes the gene for luciferin into the cancer cells. The researchers have shown that their antibody can accurately find and “light up” cancer cells. Their next step is to bond the antibody to an expression vector that carries the normal HER2 gene into mutant cancer cells.

 

5. Immunologists are investigating ways to destroy lymphocytes (white blood cells of the immune system) that have become cancerous (lymphomas). A current drug Rituximab contains antibodies that bind to the surfaces of these lymphocytes setting them up for destruction by the cancer patient’s own immune system. They are currently seeking ways to modify the antibody’s structure so that it will attract the cancer patient’s “natural killer” (NK) cells to the lymphocytes. Success of this project will bring a multi-faceted immune response against lymphomas and hasten destruction.

 

6. Biochemists have discovered a protein kinase enzyme named BRAF that is an important link in a molecular pathway that causes a cell to divide. Normally, BRAF responds to signals coming from outside the cell—signals calling for the cell to divide normally under normal conditions. But there is a mutation in BRAF enzymes that causes it activate the cell toward division continually. In this way it gives rise to melanomas and thyroid or ovarian cancers. Biochemists have also found a drug, vemurafenib, which binds selectively to mutant BRAF totally inactivating it. Cells that have inactivated BRAF undergo apoptosis—a process that leads to cell death.

 

7. Molecular biologists have taken nanoparticle-sized spheres and used them to deliver a cell-killing toxin from bee venom to tumors in mice, substantially reducing tumor growth without harming normal body tissues. Nanoparticles are known to concentrate in solid tumors because blood vessels in tumors show “enhanced permeability and retention effect” or EPR. Hence substances such as nanoparticles escape more readily from the bloodstream into tumors and the generally poor drainage of lymph from tumors further helps trap the particles in tumor tissue.

 

8. Organic chemists are exploring structural variations of the organic compound avobenzone (1-[4-Methoxyphenyl]-3-[4-tert-butylphenyl] propane-1,3-dione) for inclusion in sunblock products. Avobenzone is known for its ability to absorb a broad spectrum of ultra-violet radiations including UVB light (known to enhance the frequency of basal cell and squamous cell carcinomas [skin cancers]); and UVA rays thought to increase the frequency of melanoma cancers. New variations in the structure of avobenzone are hoped to retain the ability to absorb harmful UV radiation while having an increased stability in the presence of that radiation.

 

9. Biochemists are analyzing the many, many components of red meat (beef and pork) to determine which component, if any, will cause increased colorectal cancer rates in mice when the component is administered orally. Studies have shown that higher colorectal cancer rates in humans are associated with higher consumption rates of red meat.

 

10. Molecular biologists have developed a new sequence of human genes called an ankyrin insulator sequence. A new corrected or therapeutic gene is placed within this sequence. Its role is to create an active area on a human chromosome where the new gene can work efficiently no matter what chromosome it lands on.

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