Chemistry - Methods of retrieving salts

• bonkysleuth

  20 Apr 08, 18:01

  State whether the salts are insoluble or soluble before telling me the possible methods of retrieval of the salts. These are the salts which I am not able to decide their solubility so i ain't sure what method to use. 3 ways to get back the salt, namely titration, precipitation and acid with excess insoluble base/carbonate.

  salt :                                               solubility                              methods of retrieval

  copper(II) chloride

  lead bromid

  potassium chloride

   

  Lastly, are silver nitrate and magnesium sulphate soluble can can be prepared by the acid with excess insouble base/carbonate method?

   

  the equations are as follows: (FOR SILVER NITRATE AND MAGNESIUM SULPHATE)

  2HNO3 + MgCO3 -> 2AgNo3 + CO2 + H2O 

  Magnesium sulphate :

  H2SO4 + MgCO3 -> MgSO4 + CO2 + H2O

   

  Oh, i forgot to ask, is titration ONLY meant for getting back sodium, potassium and ammonium salts?

• UltimaOnline

  21 Apr 08, 13:23

  Titration When the desired salt is soluble, and can be prepared by using an aqueous acid and an aqueous alkali. eg. Sodium chloride from sodium hydroxide and hydrochloric acid. Titration allows for exact neutralization and hence you get a pure salt without contaimination from acid or alkali. Ionic Precipitation When the salt is insoluble, and can be prepared by using two aqueous solutions, that can either be salts, acids or alkalis. Eg. lead(II) sulphate from sulphuric acid or sodium sulphate, and lead(II) nitrate. Filter, the desired salt is the residue, the filtrate solution consists of leftover ions - in this case, HNO3 or NaNO3. Because one salt obtained is aqueous and the other (the desired salt) is solid, you can use filtration to easily separate the salts and prevent contamination of your desired salt (eg. PbSO4) by either the other salt (eg. NaNO3), or any acid (eg. H2SO4 or HNO3) if such is used or produced. Acid with excess insoluble base/carbonate. When the salt is soluble, and can be prepared by using an aqueous acid and an insoluble base/carbonate. Eg. copper(II) sulphate from sulphuric acid and copper(II) carbonate or copper(II) oxide. Basically, neutralization occurs, same as titration. Reason for difference between this method and titration is, since the base copper(II) oxide is not soluble and you cannot obtain aqueous copper(II) hydroxide, you use excess of the solid (either the oxide or the carbonate) with limited acid, so that you can easily separate (using filtration) the desired pure aqueous salt, and the excess solid. Hence, like titration, this method has its own way of preventing contaimination of the salt (by using *excess* solid here). "These are the salts which I am not able to decide their solubility". Google for a list of salts and their solubilities. "Lastly, are silver nitrate and magnesium sulphate soluble can can be prepared by the acid with excess insouble base/carbonate method?" If these salts were insoluble, you *CANNOT* use acid with base/carbonate method. Why not? This is a common exam question. Think about it. (hint : the yield will be low; the reaction will cease very quickly). "Oh, i forgot to ask, is titration ONLY meant for getting back sodium, potassium and ammonium salts?" *Never* be a dogmatic student who memorizes notes without understanding. Do *not* merely memorize "titration ONLY meant for getting back sodium, potassium and ammonium salts", but *UNDERSTAND WHY* (why this is given as a useful guideline, *NOT* a rule to be followed unthinkingly merely for the sake of obeying rules!).
• tinuviel07

  21 Apr 08, 13:29

  copper(II) chloride - soluble

  lead bromide - low

  potassium chloride - all potassium salts soluble