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• Using a Multimeter

Project Summary

Difficulty	7  –  8
Time required	Short (several days)
Prerequisites	None
Material Availability	You will need digital multimeter for this science fair project. See the Materials and Equipment list for more details.
Cost	Low ($20 - $50)
Safety	Use caution when using the handsaw. Adult supervision is recommended.

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Sponsor

Sponsored by a generous grant from the Camille and Henry Dreyfus Foundation

Abstract

Objective

To investigate whether or not a sports drink provides more electrolytes than orange juice.

Introduction

"Just do it!" You've heard the slogan, and there is no doubt that exercise is a key part of staying healthy. Most experts agree that if you are engaged in light to moderate exercise, water is just fine. But if you are exercising strenuously, you might need to replace some of the salts that your body loses through sweat. These salts, or electrolytes, are found in most sports drinks.

What are the advantages of a sports drink over water? Water will provide the liquid you need to avoid dehydration, but does not have electrolytes. An electrolyte is a substance that will dissociate into ions in a solution. The ions in the solution give it the capacity to conduct electricity. Electrolytes, such as sodium and potassium, are present in sweat, and need to be replaced during strenuous exercise. Chloride, calcium, and phosphate ions are also electrolytes.

The proper concentration of electrolytes in your blood is essential for health. Your cardiovascular and nervous systems, to name just two, require electrolytes to function. Concentration gradients of sodium and potassium across the cell membrane produce the membrane potential and provide the means by which electrochemical impulses are transmitted in nerve and muscle fibers.

The concentration of the various electrolytes in body fluids is maintained within a narrow range. Stability of the electrolyte balance depends on adequate intake of water and electrolytes. The maintenance of electrolytes within this narrow range is due to homeostatic mechanisms within the body, which control the absorption, distribution, and excretion of water and its dissolved electrolytes.

But can you get your electrolytes from natural juices, such as orange juice? One problem with juice is that many have relatively high concentrations of carbohydrates, which is fine for your morning drink, but not ideal for re-hydrating during exercise. High levels of carbohydrates add useless calories and require water for digestion.

To measure the electrolytes in this science fair project, you will use a multimeter. A multimeter is an electronic device that measures voltage, current, and resistance. For this science fair project, you will just use the ammeter part of the multimeter. An ammeter measures current.

How can you use an ammeter to measure the concentration of electrolytes? You will use it to measure conductance, which is proportional to the electrolyte concentration. Because electrolytes are charged particles that carry current in solution, the conductance of the solution depends on the concentration of the electrolytes. If you increase the concentration of electrolytes in a solution, the conductance of the solution also increases. In order to measure a current in the solutions, you have to apply a voltage. You will use a 9-volt (V) battery to supply the voltage.

Conductance is measured in units, called siemens, and has the symbol G. The symbol for current is I, and it is measured in amperes (amp). Voltage, V, is measured in volts (V). Calculating the conductance is easy—it is the current divided by the voltage, as shown below in Equation 1.

Equation 1.

G =

I  V

• G is conductance, measured in siemens.
• I is current, measured in amperes (amp).
• V is the voltage, measured in volts (V).

Terms, Concepts and Questions to Start Background Research

• Electrolyte
• Dissociate
• Ion
• Solution
• Conductance
• Electricity
• Homeostatic mechanism
• Multimeter
• Voltage
• Volts (V)
• Current
• Amps, microamps, milliamps
• Resistance
• Ohms
• Ammeter
• Proportional
• Siemens
• Direct current
• Alternating current
• Open circuit
• Dilute

Questions

• What are the amounts of sodium, potassium, and carbohydrates in one serving (8 ounces) of orange juice? How does this compare with sports drinks?
• What do electrolytes do in your body?

Bibliography

• Presidents Council on Fitness. (2008). The President's Council on Physical Fitness and Sports. Retrieved August 21, 2008, from http://www.fitness.gov/faq.htm
• How Stuff Works. (2008). What are electrolytes? Retrieved August 20, 2008, from http://www.howstuffworks.com/question565.htm

Materials and Equipment

• Copper wire, bare, 24-gauge (around 5 feet); available at most hardware stores
• Wire cutters
• Ruler
• Plastic tube from a pen, cut to about 1 inch, or small plastic toys in the shape of a tube and 1 inch long
• Handsaw to cut plastic tube
• 9-V battery
• 9-V battery clip
• Wires with alligator clips for making connections, should have clips on both ends, and be about 6 inches long (2)
• Small bowls plastic, glass, or ceramic bowls, not metal (8)
• Masking tape
• Permanent marker
• Sports drink of your choice, room-temperature
• Orange juice of your choice, room-temperature
• Distilled water (dH₂O), room-temperature; available at most grocery stores
• Tap water, room-temperature
• Measuring cup, 1/2-cup capacity
• A digital multimeter, for example, Radio Shack Catalog # 22-812. Other models are available at electronic supply and auto parts stores.
1. Note: The multimeter has various sensitivity settings. Some multimeters automatically change sensitivity, but most inexpensive ones have a dial that sets the sensitivity. Typical multimeters have a range of settings from 200 microamps up to 200 milliamps. This is a thousand-fold range. The 200-microamp setting is good for measuring from 0–200 microamps, but will not work for higher currents. The 200-milliamp setting is good for 20–200 milliamp currents, but is inaccurate for low currents (microamps).
• Paper towels
• Lab notebook

Experimental Procedure

Making a Simple Conductance Sensor

1. Using the wire cutters, cut two pieces of copper wire, each about 6 inches long.
2. Using your handsaw, cut the plastic tube into a 1-inch piece. Ask an adult for assistance with this step.
3. Wrap one piece of the wire around the tube near one end a few times, leaving about 2 inches of wire free.
4. Wrap the other piece of wire around the tube at the other end a few times, again, leaving about 2 inches of wire free. There should be no contact between the two wires, and they should be wrapped tight enough that they won't slide off of the tube. See Figure 1 for a visual aid.

Figure 1. The conductance sensor consists of a non-conducting core (plastic or rubber) with copper wire wrapped around the ends. The ions in the solution complete the circuit and allow current to flow between the copper wires.

5. Attach the battery clip onto the battery.
6. Attach one of the free copper wires on the conductance sensor (Figure 1) to the positive terminal of the 9-V battery, using the wire with one of the alligator clips.
7. Attach the other copper wire from the sensor to the black terminal of the multimeter, using the other alligator clip.
8. It does not matter which side has the positive and negative leads.
9. Note that this is an open circuit because of the gap between the wires wrapped around the non-conducting tube. You will use the electrolytes in the solutions to close the circuit. The amount of current that flows is proportional to the electrolyte concentration.

Figure 2. The circuit used to measure conductance. The multimeter measures current, I, through the circuit. As the concentration of electrolytes increases, the conductance, G, of the solution also increases, leading to a higher current. The voltage, V, is fixed at 9 V. The picture on the right shows an actual circuit.

Setting Up Your Test Solutions

1. Clean the eight small bowls with warm soapy water, rinse thoroughly, and dry them right away with a clean dry cloth or paper towel. This will remove ions in the tap water. If you want to be extra careful, rinse the bowls with distilled water before drying.
2. Put masking tape on all eight bowls.
1. Label four bowls with the following labels: Distilled Water, Tap Water, Sports Drink, and Orange Juice.
2. Label one bowl Tap Water Rinse.
3. Label the final three bowls as follows: dH₂O Rinse 1, dH₂O Rinse 2, and dH₂O Rinse 3. Use these bowls to rinse the conductance sensor between uses.
3. Pour 1/2 cup of each liquid into the appropriately labeled bowl. All of the solutions should be at room temperature.

Measuring the Conductance

1. Turn the multimeter to read direct current. Make sure it is reading direct current and not alternating current (see the instructions for the multimeter).
1. Use the 200-microamps setting to read low conductance (distilled water, for example). Use the higher settings for solutions with high electrolyte concentration (sports drink).
2. Place the conductance sensor in the distilled water. Make sure it is completely immersed.
3. Read the current on the multimeter. Move the dial to its highest sensitivity.
4. Record the current in your lab notebook in a data table.
1. The voltage is 9 V, which is obtained from the battery. The current is what you measure with the multimeter.
5. No need to rinse this time, since you used distilled water.
6. Now place the conductance sensor in the tap water.
7. Record the current. Again, make sure you are using the proper sensitivity scale.
8. Tap the sensor on a paper towel to remove drops of tap water. Then rinse the sensor in distilled water, dipping it briefly in each of the three distilled water rinse bowls.
9. Place the sensor in the sports drink and measure the current. Record the current in your lab notebook.
10. Tap the sensor dry, and then dip the sensor in tap water, then in the three bowls of distilled water.
11. Place the sensor in the orange juice and measure the current. Record the current in your lab notebook.
12. Rinse the sensor in the tap water and then in all three distilled water bowls.
13. Place the sensor in the sports drink and measure the current. Record the current in your lab notebook.
14. Rinse the sensor in the tap water and then in all three distilled water bowls.
15. Repeat Measuring the Conductance steps 1-14 two more times to obtain a total of three measurements for each liquid. Record all data and measurements in the data table in your lab notebook.
16. Average your results.
17. Convert microamps to amps by dividing by 1,000,000. Convert milliamps to amps by dividing by 1,000.
18. Calculate the conductance by using Equation 1, shown in the Introduction.
19. Which liquid has the highest conductance, meaning the most electrolytes?
20. What could you do to make your own sports drink, starting with orange juice?
1. If the carbohydrates in the orange juice are higher than they are in the sports drink, dilute the juice so that the carbohydrates are about the same as they are in the sports drink. How does the conductance of the diluted juice compare to that of the sports drink?

Variations

• Try other sports drinks and juices.
1. What is the conductance of fresh-squeezed orange juice?
2. What about lemonade?
• Make a conductance sensor using a microphone jack (immerse the plug in the liquid).
• Standardize your readings, using tap water as a reference. Divide all of the current measurements for each trial by the current you measured for the tap water. Tap water will have a conductance of 1.0. The fruit juice and sports drinks will then have conductances that are multiples of the tap water's conductance.

• For more science project ideas in this area of science, see Chemistry Project Ideas.

Credits

David Whyte, PhD, Science Buddies

This project is based on the following 2008 California State Science fair project, a winner of the Science Buddies Clever Scientist Award:
Yaeger, T.O. Jr. (2008). Electrolyte Madness. Retrieved August 18, 2008, from http://www.usc.edu/CSSF/History/2008/Projects/J0516.pdf

Last edit date: 2008-11-13 10:25:00

Career Focus

If you like this project, you might enjoy exploring careers in Chemistry.

	Chemist Everything in the environment, whether naturally occurring or of human design, is composed of chemicals. Chemists search for and use new knowledge about chemicals to develop new processes or products.			Chemical Engineer Chemical engineers solve the problems that affect our everyday lives by applying the principles of chemistry. If you enjoy working in a chemistry laboratory and are interested in developing useful products for people, then a career as a chemical engineer might be in your future.
	Chemical Technician The role that the chemical technician plays is the backbone of every chemical, semiconductor, and pharmaceutical manufacturing operation. Chemical technicians conduct experiments, record data, and help to implement new processes and procedures in the laboratory. If you enjoy hands-on work, then you might be interested in the career of a chemical technician.

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