#### • Class 11 Physics Demo

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#### • definition of chemical solution

Question:The solution remaining from Part A, which contains 0.0100 M Ni 2+ and Fe 2+ ions, is still saturated with H2S gas, producing a concentration of 0.100 M. A buffer is added to this solution to produce a pH of 2.76 . Which of the following describes correctly the effect of the addition of the buffer? Only NiS precipitates Only FeS precipitates Both precipitate Neither precipitate Kspa for the metal sulfides FeS = 6*10^2 NiS = 8*10^-1 any help is much appreciated

Answers:Only NiS precipitates. Precipitates when Q>K Q=concentration products/concentration reactants Q=[product ion][product ion]/[H30]^2 for this problem Q= (.01M ion Ni or Fe)(.1M H2S)/[H3O]^2 H30 was given in part A, but here pH is given instead of H+ concentration, so, convert p function to concentration, 10^(-2.76)=.00174 M H30 aka M H+ so plug it in Q= (.01M ion Ni or Fe)(.1M H2S)/(.00174^2 M H30) Q= 330.3 330.3>8E-1 so NiS precipitates 330.3<600 so FeS does not precipitate

Question:

Answers:Revised my answer a bit for you after clarifying my own understanding! Ksp= the concerntration of ions in solution which has been worked out experimentally and can be looked up. ie in BaSO4 Ksp = [Ba2+][SO42-] A low Ksp indicates a low solubility because the values of these concerntrations (only this amont of the compound will be in the form of ions and the rest will form precipitate) will be low. As soon as the concertration of the ions in the solution exceeds the Ksp value a preciptate will appear. An example: BaF2(aq) --> Ba2+(aq) + 2F-(aq) (reversible reaction) Ksp = [Ba2+] [F-}2 = 1.7x10-6 100mL BaNO3 (0.2molL-1) is added to 400mL NH4F at 25oC. Will a precipitate of BaF2 appear? Before precipitation [Ba2+] = (0.2{molar conc}*0.1{vol of Ba compund added})/0.5{total vol of solution} = 0.04mol/L [F-] = (0.5*0.4)/0.5 = 0.4 mol/L Since [Ba2+][F-] = 6.4x10-3 is larger than Ksp of 1.7x10-6 a precipitate will form

Question:Can it refer to any solid, or does it have to have a specific chemical formula/structure? Thanks for any help.

Answers:A precipitate is a solid formed from a previously clear solution through a chemical reaction. There is no specific solid that is referred to as "precipitate", because precipitates differ depending on the reactions involved. Mixing a solution of a fluoride salt with a lanthanum nitrate solution will precipitate lanthanum fluoride, while mixing a solution of a bromide salt with a solution of silver nitrate will precipitate silver bromide, for example. The two precipitates (LaF3 and AgBr) are the insoluble products.

Question:I would like about 3-5 steps about how to carry a precipitation experiment... I already worked out titration, and reacting a carbonate with a metal... and this is the last one of the experiments. My problem is I need to make the steps in general therefore not mentioning any compounds... Any help would be greatly appreciated Thanks

Answers:Well, I'll explain precipitation reactions for you. Basically, you take two ionic compounds, both aqueous, and get an insoluble precipitate. Lemme explain it like this: Your two compounds are silver nitrate and sodium chloride. AgNO3 and NaCl. The ions really aren't happy in their relationships. They try, but in all honesty the silver just hovers around in solution, away from the nitrate, and the sodium and chloride do the same. So you've got all four floating around, and things just fall apart even more. They know that it's wrong, but one day silver and chloride bump into each other and things just fall into place. They just work so much more closely than with their previous partners, and before they know what's happened they've done the unthinkable and precipitated together into a solid. Meanwhile, sodium and nitrate wander around together anxiously. They try to work things out, but they're no better with each other than they were with Ag and Cl. Eventually, they both admit that it's too late for happiness. AgCl get married. Na drinks himself into a stupor. NO3 spends all her time talking about silver until her friends desert her. Long story short, precipitation is about failure and heartbreak. Keep that in mind.