Ionic compounds tend to be strong electrolytes, while QUESTION: Which of the following is a strong electrolyte? A. HCl, B. C6H12O6, C. H2S, C. NH3 Ionic compounds tend to be strong electrolytes, while molecular compounds are nonelectrolytes, except molecular acids and molecular bases. Most molecular acids and bases are weak electrolytes. H2S  H+(aq) + HS-(aq) NH3(aq) + H2O(aq)  NH4+(aq) + OH-(aq) A small fraction of molecules are ionized. Exceptions: the six strong electrolytes HClO4, HNO3, H2SO4, HCl, HBr, HI SCRIPT: Which of the following is a strong electrolyte? A. HCl, B. C6H12O6, C. H2S, C. NH3 PAUSE CLICK An electrolyte is a substance that, when dissolved in water, produces a mixture that conducts electricity. Water is a very poor electrical conductor. Ionic compounds tend to be strong electrolytes, while molecular compounds tend to be nonelectrolytes, except for molecular acids and bases. So the first thing we need to do is look for an ionic compound among the choices given. By now, you should be able to classify a compound as ionic or molecular based on the formula. All the choices given here are molecular. In general, molecular compounds are nonelectrolytes. This means that we need to find the exception in order to answer this question. Choice B, glucose, HIGHLIGHT C6H12O6 is a nonelectrolyte. If you add it to water, the resulting mixture will still not conduct electricity. So what are the exceptions? Molecular acids and bases are mostly weak electrolytes. A molecular acid is made up of molecules that have hydrogen and have a tendency to break up into ions when dissolved in water. An example is H2S. When we dissolve HS in water, a small fraction of H2S molecules will break up into hydrogen ions HIGHLIGHT H+ in chemical equation and hydrogen sulfide ions ions. HIGHLIGHT HS- in chemical equation One thing all molecular acids have in common is that they produce hydrogen ions when dissolved in water. However, most of the H2S molecules will remain intact. The neutral H2S molecules will not be able to complete an electric current. So H2S is considered a weak electrolyte. The resulting mixture is not a very good electrical conductor Molecular bases constitute another class of molecular compounds that are weak electrolytes. The most common example you’ll encounter is ammonia. Ammonia molecules react with water to form ammonium ions and hydroxide ions, producing a mixture that is able to conduct electricity. But just like H2S, only a small fraction of NH3 molecules are ionized. Ammonia is also a weak electrolyte. Since most… HIGHLIGHT “Most” molecular acids and bases are weak electrolytes. But we are being asked for a strong electrolyte. Among molecular compounds, there are only six known strong electrolytes. These are the six strong acids that you just have to memorize. HIGHLIGHT formulas as acids are mentioned perchloric acid, nitric acid, sulfuric acid, hydrochloric acid,…which is given in choice A hydrobromic acid, and hydriodic acid. The correct answer is A. PAUSE END RECORDING

Video ID: 1-25-3 © 2008, Project VALUE (Video Assessment Library for Undergraduate Education), Department of Physical Sciences Nicholls State University Author: Glenn V. Lo Narrator: Funded by Louisiana Board of Regents Contract No. LA-DL-SELECT-13-07/08