Science Buddies: "Ask an Expert"

Can someone please help me with steps 6-9 in the experiment "Electrolyte Challenge: Orange Juice vs. Sports Drink"? I followed the diagram but my digital multimeter continually showed a reading of 0. It has 2 settings for current: 200mA and 10A. I attached the red wire (+) of the battery clip of the 9v battery to the black probe wire of the multimeter using a wire with alligator clips on both ends. I attached the black wire of the battery clip (-) to one of the copper wires on the sensor using another wire with alligator clips on both ends. I attached the red probe of the multimeter to the other copper wire on the sensor using a third wire with alligator clips on both ends. I placed the sensor in a 1/2 cup of Gatorade. I turned on the multimeter and turned the dial to the 200 mA setting. It showed a reading of 0. What did I do wrong? Please help me!

shivamt - I have two comments. First, the polarity is reversed on your meter connection. The + terminal (red) of the battery should be connected to the + terminal (red) of your meter. There may be a polarity protection diode in the meter that is protecting the instrument and therefore not showing a reading. I'm also concerned that if your meter's lowest current range is 200 mA (milliamps). You will probably not see that kind of current flow through the electrolyte. Most multimeters, even low cost meters have a lower end current range of perhaps 200 uA (microamps). You will certainly need that kind of sensitivity when measuring very slightly ionized liquids like distilled water. The Science Buddies description of this experiment mentions the 200 uA range for example.

Rick Marz

Hi shivamt,

I just wanted to let you know that quite a few people have had problems with this project. Part of the problem is the diagram is labeled incorrectly. If you want to look at the other posts in the forum for more advice, just type "electrolyte challenge" in the search box located at the top of the page.

Good Luck!

tzforbes