EP 10 Can pure water conduct electricity？
In this lesson, we are going to explore the conductivity of different liquids, discuss whether pure water can conduct electricity, and find out which kind of liquid in our daily life has the best electrical conductivity.
NGSS - NEXT GENERATION SCIENCE STANDARDS - MIDDLE SCHOOL (MS)
Matter and its Interactions- MS-PS1-2
Engineering Design - MS-ETS1-1, MS-ETS1-3
To know whether an object is conductive, we can use a Conductivity Sensor Switch to check it out. Connect the conductivity switch, Mainboard, and OLED module as the way shown below. Switch the display module to “i12”, and connect two Alligator Clip Test Cables with the Conductivity Sensor.
1.Explore whether some daily-used stuff has electrical conductivity, like tissue, scissors, wood, etc. (There will be a lightning bolt symbol displayed on the OLED module if the object is conductive.)
2.Will the result be different when the tissue is wet?
3.Try to figure out some conductive liquids in our daily life.
In this activity, your group will use a conductivity switch to detect the conductivity of different liquids. Meanwhile, try exploring whether the distance of two Alligators clips will influence the conductivity of a solution.
Prepare 5 cups(glass, plastic, or disposable cups) and then pour 50ml vinegar, baking
soda, soapy water, distilled water and rice wine into the cups respectively.
2.Connect the Conductivity Switch
Connect the conductivity switch with the OLED module, power source(4.5V) and power-mainboard. Attach the two alligators clips on the conductivity switch. The hardware connection for detecting liquid electric conductivity is done.
3.Connect an LED with two Alligator Clips
To detect the effect of distance of alligator clips on liquid conductivity, we have to connect another set of tools.
Connect the LED long lead to red alligator clip cable, the short lead goes to the black cable.
4.Connect LED with Battery Box
Connect a red alligator clip cable to a 6V battery box’s red wire, then connect the
box’s black wire to the black alligator clip cable on the LED’s short lead.
5.Fix the Alligator Clips cable
Use tape to fix the alligator clip cables.
Tips: The front end of the alligator clips should not be touched together, or it will be dangerous!
6.Put the Alligator clips into the Liquids
Place the fixed alligator clip cables into a liquid, observe and record.
Tips: To improve the detection accuracy, please wipe the alligator clips with clean tissues before you put them into different liquids, and try to remove all the remained liquids.
Now, place the alligator clips into different liquids, and see if there is a lightning bolt symbol appearing on the OLED module, at the same time, observe the brightness change of the LED, will the LED’ s brightness be different for various liquids?
Copy the Data Table below into your notebook.
In your groups discuss the following questions:
1.Can every cup of liquid conduct electricity? Which liquid has the best electrical conductivity?
2.Is the LED brightness all the same for different liquids?
3.Will the water temperature affect its electrical conductivity? Set up an experiment and explore.
4.Does the distance between the alligator clips influence the brightness of the LED? Try Separating them by 5cm or 10, then record data in the table above.
●Dissociation - physical process accompanying the dissolution of an ionic compound in which the compound’s constituent ions are solvated and dispersed throughout the solution
●Electrolyte - substance that produces ions when dissolved in water
●Nonelectrolyte – substance that does not produce ions when dissolved in water
●strong electrolyte – substance that dissociates or ionizes completely when dissolved in water
●weak electrolyte – substance that ionizes only partially when dissolved in water
When some substances are dissolved in water, they undergo either a physical or a chemical change that yields ions in solution. These substances constitute an important class of compounds called electrolytes. Substances that do not yield ions when dissolved are called nonelectrolytes. If the physical or chemical process that generates the ions is essentially 100% efficient (all of the dissolved compound yields ions), then the substance is known as a strong electrolyte. If only a relatively small fraction of the dissolved substance undergoes the ion-producing process, it is called a weak electrolyte.
Substances may be identified as strong, weak, or nonelectrolytes by measuring the electrical conductance of an aqueous solution containing the substance. To conduct electricity, a substance must contain freely mobile, charged species. Most familiar is the conduction of electricity through metallic wires, in which case the mobile, charged entities are electrons. Solutions may also conduct electricity if they contain dissolved ions, with conductivity increasing as ion concentration increases. Applying a voltage to electrodes immersed in a solution permits assessment of the relative concentration of dissolved ions, either quantitatively, by measuring the electrical current flow, or qualitatively, by observing the brightness of a light bulb included in the circuit (Figure 1).
Figure 1. Solutions of nonelectrolytes such as ethanol do not contain dissolved ions and cannot conduct electricity. Solutions of electrolytes contain ions that permit the passage of electricity. The conductivity of an electrolyte solution is related to the strength of the electrolyte.
Pure water is an extremely poor conductor of electricity because it is only very slightly ionized—only about two out of every 1 billion molecules ionize at 25 °C. Water ionizes when one molecule of water gives up a proton to another molecule of water, yielding hydronium and hydroxide ions.
Consider the following questions:
1.Why the LED’s brightness is different for different liquids?
2.Can you explain the relation between the distance of alligator clips and the LED brightness according to the experiment result?