A 250.0 g sample of a white solid is known to be a mixture of KNO...

Question

A 250.0 g sample of a white solid is known to be a mixture of KNO3, BaCl2, and NaCl. When 100.0 g of this mixture is dis-solved in water and allowed to react with excess H2SO4, 67.3 g of a white precipitate is collected. When the remaining 150.0 g of the mixture is dissolved in water and allowed to react with excess AgNO3, 197.6 g of a second precipitate is collected. 
(a) What are the formulas of the two precipitates?

Accepted Answer

Hey everyone in this example we have three a quick solutions mixed together to form a single solution containing each of the given compounds and we need to figure out which compound would form a solid that will precipitate if any. So what we should imagine is a beaker containing each of the cat ions from the compound. So we have the N. A. Plus Catalan from the first compound, the C. A. Two plus Catalan from the second compound and the PB two plus catamaran from the third given compound. And our next step is to focus on the ann ions present in each of the compounds. So we have the S two minus sulfide an ion, we have the chloride an ion and then we have the acetate an ion. So what we should recognize is for focusing on our first carry on. We have the N. A. Plus carry on. We want to recognize that N. A. Plus is a group one A carry on. And we want to recall that group when a cat ions are always soluble. And so no matter if we pair sodium or the sodium carry on with the cl minus or the acetate, it's not going to form a precipitate. It's going to always have the accu label. So it's going to form Aquarius compounds. So therefore we would rule out considering that, carry on and move on to the next caravan which is C. A. Two plus. So if we combine our calcium carryin with the sulfide from the first compound, we would form C. A. S. When we crossed the charges and we would recognize that this is a sulfide compound. So we would recall our cell viability rules for sulfides and we would recognize that this sulfide is bonded to calcium and recall that calcium is an alkaline earth metal. So we want to recall that when sulfides are bonded to an alkaline earth metal, it would therefore be considered actually a Q. Or soluble. So this is actually going to be an acquis compound, Therefore not a solid precipitate. So we wouldn't consider calcium sulfide but we can now imagine calcium acetate. And we want to recall that for the sake ability rules of acetate acetate are always soluble. So because acetate are always soluble, forming calcium acetate would therefore form a soluble acquis compound. And so we can rule out considering calcium as a catamaran that would form a precipitate. And lastly we can focus on our lead caddy on. So first if we combine our lead Catalan with the sulfide, an ion, we would form PB us and we would form a sulfide cat ion or sorry, a sulfide compound where when we recall our sustainability rules for sulfides, we would recognize that sulfides are generally insoluble and because it's bonded to lead which is not one of the exceptions listed for sulfides beings being soluble, it's therefore going to be an insoluble solid precipitate. And so we would definitely consider this as a correct answer choice. Now our next step is to consider lead being bonded to a chloride atoms. We're a chloride an ion. So we would form P BCL two and recognize that this compound is a chloride, recalling our Celje bility rules for chlorides. We would recall that chlorides are generally going to be soluble except for the fact when it's bonded to an atom like lead two plus. So because lead two plus is an exception to the soluble itty. For chlorides, this would form a solid precipitate product. And so this is going to be our second final answer for a potential solid precipitate that would form from our solution. So everything boxed in yellow represents our final answers. If you have any questions, please leave them down below and I will see everyone in the next practice video.

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