1. Always wear safety goggles. Currently Working 2. Rinse the well plate and graduated cylinder in the sink. 3. Test the light by placing both terminals of the lighting device on the piece of metal. Does the light turn on? If not, ask for help. 4. Use the graduated cylinder to measure 10 ml of hydrochloric acid (HCl). Pour the acid into well # 1. 5. Put both terminals of the lighting device into well #1. Does the light turn on? If not, ask for help. 6. Now put the following solutions into the other wells: 10 ml water (H O) into well #2. 2 10 ml sugar solution (C 12 H 22 O 11 ) into well #3. 10 ml salt solution (NaSO 4 ) into well #4. 7. Test each of the wells by putting both terminals of the lighting device into wells #2, #3, and #4. Rinse the terminals in the Rinse Beaker between solutions. Does the light turn on? Why do only some of these liquids make the light work? 8. Rinse the well plate and graduated cylinder in the sink. 2009 OMSI Why do some solutions conduct electricity? A Closer Look When an acid, a base, or a salt is dissolved in water, the molecules break into electrically charged particles called ions. Solutions with ions conduct electricity. Because pure water has few ions, it is a poor conductor. Uncharged molecules that dissolve in water, like sugar, do not conduct electricity. A battery is a device to store energy in chemical form. When the two terminals of the battery are connected by something that conducts electricity (like a copper wire or a solution that contains ions), the energy can be used to do work make light or run a motor.
Talking Points: Currently Working Extensions Try this experiment: 1) Add a mixture of both salt solution and sugar solution. Does it conduct? It does. There is enough salt to carry the current. Ask this question: 1) What is needed to carry an electric current? An electric current exists when charged particles move. In this experiment electrons move through the wire and ions move through the solution (if they are present). Applications When the two terminals touch the piece of metal, the current is carried entirely by electrons that can move through the wire and metal. But if the two terminals are connected by a solution, the current is carried only if there are charged particles, called ions, in the solution to carry it. If there is, positive ions will move in one direction, negative ions will move in the opposite direction, and the electric current can move and can do work as it moves. Practical applications range from automobile batteries (the solution is sulfuric acid) to electroplating (the solution contains a dissolved salt of the metal being plated). Solutions that conduct electricity are very important to functions of the human body. For example, messages are sent from your brain to other parts of your body (and vice versa) as electrical impulses carried by ions that are dissolved within your nervous system. In-Depth Information An ion is an atom or group of atoms with an electric charge. All acids, for example, contain the hydrogen ion H +, along with a negative ion to balance the charge. Hydrochloric acid contains H + and Cl - ions. Salt solution contains Na + and Cl - ions. When ions are present in the solution, these ions can move through the solution to carry an electric current. Pure water and sugar solution do not contain ions in significant numbers. Sugar molecules do not break down into ions when dissolved. Therefore, these solutions cannot carry an electric current. Why does salt break down into ions? Why doesn t sugar? Salt is made up of sodium and chlorine. You will notice these elements (Na and Cl) lie at opposite ends of the periodic table. Atoms at the left of the table (like sodium) hold one electron very loosely and easily give it up to become positive ions; atoms at the right (like chlorine) lack only one electron to complete their outer electron shell and attract electrons strongly to become negative ions. Both in solid crystals (table salt) and in solution, sodium chloride consists of Na + and Cl - ions. Both in molten salt and in a salt solution the ions will carry an electric current very nicely. Sugar, sucrose, C 12 H 22 O 11, is a stable molecule that dissolves readily in water, but in solution it retains its molecular structure. It releases no charged ions capable of carrying an electric current.