Thio: usually means replacement of oxygen by sulfur QUESTION: The formula of thiosulfate ion is… A. S2O32-, B. S2O62- , C. S2O42-, D. S2O82- Thiosulfate is S2O32-. Names and formulas of polyatomic ions are trivial information --- just memorize. Thio: usually means replacement of oxygen by sulfur SO42- is sulfate, S2O32- is thiosulfate SO32- is sulfite, S2O22- is thiosulfite OCN- is cyanate, SCN- is thiocyanate, CN- is cyanide S2O62- is dithionate, S2O42- is dithionite S2O82- is persulfate or peroxydisulfate SCRIPT: (NOTE: thio rhymes with Ohio) The formula of thiosulfate ion is A. S2O3 with a –2 charge B. S2O6 with a –2 charge C. S2O4 with a –2 charge Or D. S2O8 with a –2 charge PAUSE CLICK The correct answer is choice A. Thiosulfate is S2O3 with a –2 charge. CLICK Names and formulas of polyatomic ions are trivial information. In other words, you just need to memorize them as part of the basic vocabulary of Chemistry. Whether or not your teacher requires you to memorize them, it’s a good idea to just memorize them. It’s difficult to memorize these names and formulas in isolation. It’s better if you try to memorize them in groups based on similarities. Here’s a few relationships you might find useful. HIGHLIGHT FORMULAS AS THEY ARE DESCRIBED. The prefix thio usually means replacement of oxygen by sulfur. CLICK You should know that sulfate is SO4 with a –2 charge We replace one of the oxygen atoms with a sulfur atom…. This gives us two sulfur atoms and three oxygen atoms. S2O3 with a –2 charge is thiosulfate. CLICK Similarly, replacing one of the oxygen atoms in sulfate by sulfur gives us thiosulfite… S2O2 with a –2 charge. CLICK OCN with a -1 charge is cyanate…. Replacing the oxygen by sulfur, we get SCN with a -1 charge…, this ion is called thiocyanate. You can see that “cyan” is associated with carbon and nitrogen. In fact, cyanide, is CN with a –1 charge. The other choices given here are all commonly-occurring ions containing sulfur. Choice B, S2O6 with a –2 charge is dithionate. Choice C. S2O4 with a –2 charge is dithionite. This is one case where ions with “ate” and “ite” do not differ by only one oxygen. Instead, the dithionate has two more oxygen atoms compared to dithionite. CLICK Finally, choice D, S2O8 with a –2 charge is called persulfate, or peroxydisulfate. PAUSE END RECORDING

Video ID: 1-22-8 © 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