Which of the following is insoluble in water? QUESTION: Which of the following is insoluble in water? A. Na2CO3, B. MgSO4, C. PbCl2, D. CaS Solubility rules (for common ionic compounds): Compounds of the following are always soluble: sodium, potassium, ammonium, nitrate, nitrite, perchlorate, acetate Compounds of the following are generally soluble: chloride, bromide, iodide --- except with silver, lead(II), mercury(I), and copper(I) Sulfate -- except with lead(II), barium, strontium, calcium, and mercury(I) Fluoride --- except with lead(II) and group II(A) The rest are generally insoluble. Exceptions: sulfides of group II(A) are soluble hydroxides of calcium, strontium and barium are moderately soluble. Which of the following is insoluble in water? Sodium carbonate…. Magnesium sulfate…. Lead(II) chloride… Or Calcium sulfide PAUSE CLICK To answer this question, use the solubility rules for common ionic compounds…. You’re likely to see different versions of these rules in different textbooks. They’re all pretty much equivalent, although some textbooks include more ions than others. In general, the rules will tell you CLICK which compounds are always soluble… CLICK which compounds are generally soluble and what the exceptions are…. And that pretty much anything else is insoluble and what the exceptions are. Let’s apply the rules to each of the choices. Let’s start with choice A…. Sodium carbonate CALLOUT “sodium carbonate” pointing to Na2CO3 This compound contains sodium ions… HIGHLIGHT Na in Na2CO3, HIGHLIGHT “sodium” in rule 1 The first rule tells us that common ionic compounds that have sodium ions are soluble in water. Therefore, sodium carbonate is soluble in water. Choice A is incorrect. CROSS OUT Choice A How about choice B… magnesium sulfate… CALLOUT “magnesium sulfate” pointing to MgSO4 Rule 1 does not apply. It doesn’t say anything about magnesium. And it doesn’t say anything about sulfate. So, we move on to the second rule. The second rule tells us that sulfates are generally soluble. HIGHLIGHT Sulfate rule … unless it is in combination with lead(II), barium, strontium, calcium or mercury(I). The compound we’re given is magnesium sulfate. Therefore, the compound is soluble. Choice B is also incorrect. CROSS OUT Choice B How about choice C…lead(II) chloride? CALLOUT “lead(II) chloride” pointing to PbCl2 Again, the first rule does not apply. It doesn’t say anything about lead or chloride. So, we go on to the next rule. It says that chlorides are generally soluble. HIGHLIGHT chloride rule …. Unless it is in combination with silver, lead(II), copper(I), or mercury(I) …Our compound is lead(II) chloride… HIGHLIGHT “except with lead(II)” … therefore, it is an exception to the rule. Lead(II) chloride is insoluble. Therefore, choice C is the correct answer. Let’s verify that choice D is, in fact, incorrect. The compound in choice D is calcium sulfide…. CALLOUT “calcium sulfide” pointing to CaS Rule 1 does not apply. It doesn’t say anything about calcium or sulfide. Rule 2 does not apply either. So, we move on to rule 3, which says that compounds not covered in rules 1 and 2 are generally insoluble, and what the exceptions are. Referring to a periodic table, we find that calcium belongs to group two A. HIGHLIGHT Group II(A) Therefore, calcium sulfide is an exception. It is soluble. CROSS OUT choice D. PAUSE END RECORDING

Video ID: 5-5-1 © 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